Big Java / Java Concepts Lab 14Buttons

1. All problems in this lab are based on the HelloTester program:

/** File HelloTester.java */ import javax.swing.JFrame; public class HelloTester {     public static void main(String args[])     {     JFrame frame = new HelloFrame();         frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);         frame.setTitle("HelloTester");         frame.setVisible(true);     } } /** File HelloFrame.java */ import javax.swing.JFrame; import javax.swing.JLabel; import java.awt.BorderLayout; import java.awt.Font; public class HelloFrame extends JFrame {     public HelloFrame()     {         message = "Hello, World!";         label = new JLabel(message);         label.setFont(new Font("serif", Font.PLAIN, DEFAULT_SIZE));         add(label, BorderLayout.CENTER);         setSize(FRAME_WIDTH, FRAME_HEIGHT);     }     private String message;    private JLabel label;     private static int FRAME_WIDTH = 300;    private static int FRAME_HEIGHT = 300;    private static int DEFAULT_SIZE = 20;}

In this problem, you need to add two buttons to the bottom of the frame, like this:

Follow these steps:

1. Make two instance variables of the class JButton:private JButton smallerButton;private JButton largerButton;

2. Create a method called createSouthPanel and place the following two lines inside the method to initialize the variables with JButton objects:smallerButton = new JButton("Smaller");largerButton = new JButton("Larger");

3. Place the buttons into a panel:JPanel southPanel = new JPanel(); southPanel.add(smallerButton);southPanel.add(largerButton);

4. Add the south panel to the frame:

add(southPanel, BorderLayout.SOUTH);

5. In the frame constructor, call the method createSouthPanel:

createSouthPanel();

Make these changes in your program. Run the program to confirm that the buttons appear.

(a) What happens when you click the buttons? Why?

(b) Provide the source code for your createSouthPanel method.

2. Next, you need to connect the buttons to actions. For each button, carry out these steps:

1. Create a class that implements the ActionListener interface and override the actionPerformed method.

2. Make an object of that class.

3. Install that object as the action listener of the button.

Perform these steps one at a time.

When the "Larger" button is clicked, we want to increase the font size by 25 percent. When the "Smaller" button is clicked, we want to decrease it. To avoid integer rounding errors, keep a floating-point instance variable fontSizeFactor that is initialized with 1. Clicking on the buttons multiplies by 1.25 or 0.8 (because 0.8 = 1/ 1.25).

private double fontSizeFactor = 1;

Here is an appropriate action listener for the "Larger" button.class LargerFontListener implements ActionListener {    public void actionPerformed(ActionEvent event)    {       fontSizeFactor = 1.25 * fontSizeFactor;       label.setFont(new Font("serif", Font.PLAIN,             (int) (DEFAULT_SIZE * fontSizeFactor)));       label.repaint();    } }

Place this class inside the createSouthPanel method, since actionPerformed needs to access the panel and fontSizeFactor variables.

To connect it to the "Larger" button, you need to create an object of this class and set it as an action listener of the button. Place the following instructions into the frame constructor:

ActionListener largerListener = new LargerFontListener(); largerButton.addActionListener(largerListener);

Add the code, compile the program, and run it. Don't add the code for the "Smaller" button yet.

Click on both buttons several times. What happens?

3. Repeat the steps above for the "Smaller" button. Make an action listener class and add an instance of that class as an action listener of the smallerButton. Run your program. Both buttons should work.

Provide the complete code for the createSouthPanel method.

Layout Management

4. In the preceding program, the buttons were placed on the bottom of the frame, next to each other. Change your program so that they are placed on the right of the frame, one above the other other.

What is the code for the HelloFrame class now?

Menus

5. In this program, we will use a menu instead of a set of buttons to increase and decrease the font size.

As with buttons, you need to solve two unrelated issues: How to place the menu items How to connect actions to the menu items.

In Java, there is a three-level hierarchy for menus.1.   A menu bar is attached to a window. 2.   The menu bar contains menus, rectangular panels with menu strings inside

them. 3.   Menus contain submenus and menu items.

Only menu items have actions associated with them.

Here are the instructions to build the menu for this program.JMenuBar menuBar = new JMenuBar(); setJMenuBar(menuBar);

JMenu fontMenu = new JMenu("Font"); menuBar.add(fontMenu);

JMenuItem largerItem = new JMenuItem("Larger"); fontMenu.add(largerItem);

JMenuItem smallerItem = new JMenuItem("Smaller"); fontMenu.add(smallerItem);

Start again with the HelloFrame class.

Create a method called createMenu, and place these instructions inside this method.

Run yor. (a)

Run your program and check that the menu works. Don't forget to call createMenu from within the constructor. (a) What is the code for your HelloFrame class? (b) What happens when you select a menu item?

6. Next, you need to attach actions to the menu items. This process is identical to attaching actions to buttons.

Attach the actions to the two menu items and run your program. Check that selecting the menu items respectively increases and decreases the font size.

What is the complete source code for your frame class now?

Combo Boxes

7. In this exercise, you will see how to offer a user a selection among multiple choices. You can place all choices into a combo box.

To build such a combo box, you add items to it:final JComboBox comboBox = new JComboBox(); comboBox.addItem("Small"); comboBox.addItem("Medium"); comboBox.addItem("Large"); comboBox.addItem("Extra Large");

Then place the combo box in the south end of the content pane.

add(comboBox, BorderLayout.SOUTH);

Add a createSouthPanel method and paste the lines indicated above inside the method. Try it out. Don't forget to call the createSouthPanel method from within the constructor. Run the program and compare it against the figure.

The program looks different. Why?

8. The border layout grows all items to their maximum size. To avoid this, enclose the combo box inside a panel, even though it is a single item.JPanel southPanel = new JPanel(); southPanel.add(comboBox); add(southPanel, BorderLayout.SOUTH);

Try it out. Add the combo box to the frame of the HelloTester program. Compile and run the program. Pull down the item list of the combo box to see the items.

What happens if you select one of the items?

9. To activate the combo box, you need to attach an action listener. The actionPerformed method needs to determine which item the user selected.class ComboListener implements ActionListener {    public void actionPerformed(ActionEvent event)    {       String item = (String) comboBox.getSelectedItem();       . . .    } }

You need to cast the return value of the getSelectedItem method to a String because it is possible to put other objects, such as icons, into a combo box.

Now you simply set the correct font size, depending on the item string.int messageSize = DEFAULT_SIZE; if (item.equals("Small")) { messageSize = SMALL_SIZE; } else if (item.equals("Medium")) { messageSize = MEDIUM_SIZE; } else if (item.equals("Large")) { messageSize = LARGE_SIZE; } else if (item.equals("Extra Large")) { messageSize = EXTRA_LARGE_SIZE; } label.setFont(new Font("serif", Font.PLAIN, messageSize)); label.repaint();

Define the size constants as follows:public static final int SMALL_SIZE = 12; public static final int MEDIUM_SIZE = 18; public static final int LARGE_SIZE = 24; public static final int EXTRA_LARGE_SIZE = 36;

Add the combo action listener and try out your program. When you select an item from the combo box, the message should be displayed in the appropriate size.

Provide the complete source code for your createSouthPanel method.

Radio Buttons and Check Boxes

10. Radio buttons are another way to offer the user a selection among multiple alternatives.

These buttons are called radio buttons because they work like the channel buttons on a radio. When you select a radio button, the previously selected radio button is turned off.

However, radio buttons take up more screen "real estate" than combo boxes and therefore are best used when you need to offer users only a small selection.

Here are the instructions to construct two radio buttons:helloButton = new JRadioButton("Hello"); goodbyeButton = new JRadioButton("Goodbye") ;

To get the "radio button" effect, where all other buttons are turned off when one of the buttons is clicked, you need to place the buttons in a button group:

ButtonGroup group = new ButtonGroup(); group.add(helloButton);

group.add(goodbyeButton);

Finally, you want to turn the first button on:

helloButton.setSelected(true);

The button group is a logical grouping of the buttons. You still need to physically lay out the buttons on the screen:JPanel southPanel = new JPanel(); southPanel.add(helloButton); southPanel.add(goodbyeButton); add(southPanel, BorderLayout.SOUTH);

Add the two radio buttons to the frame of the HelloTester program. Add a createSouthPanel method, just like you did in the previous problems. (a) What is the code for your HelloFrame class? (b) Run the program. What happens when you click the radio buttons?

11. Now change the message text when the user clicks a radio button. To assemble the correct text, simply check which button is currently selected.class MessageListener implements ActionListener {    public void actionPerformed(ActionEvent event)    {       String message = "";       if (helloButton.isSelected()) message = "Hello";       else if (goodbyeButton.isSelected()) message = "Goodbye";       message = message + ", World!";       label.setText(message);    } }

Note that you can attach the same action object to both buttons.

Add the action listener and attach it to the radio buttons. Run the program. Observe how clicking the buttons changes the message text.

What is the complete source code for your HelloFrame class?

12. Check boxes are used to allow users to select a single logical alternative, typically of the form "do X" or "do nothing". Here, a check box is used to allow the user to specify whether the word "cruel" should be added to the message text:

Follow these steps to add the check box to the program.

1. Construct the check box.

cruelCheckBox = new JCheckBox("Cruel");

2. Attach the same action listener to the check box and the radio buttons.

cruelCheckBox.addActionListener(listener);

3. Add the check box to the south panel.

southPanel.add(cruelCheckBox);

4. In the actionPerformed method of the MessageAction class, check

if (cruelCheckBox.isSelected()) . . .

Run the program. Observe how clicking the check box changes the message text.

What is the complete source code for your HelloFrame class now?

Big Java / Java Concepts Lab 15Throwing Exceptions

1. The BankAccount class has three methods with preconditions:

1. the constructor (initial balance must not be negative)

2. the withdraw method (withdrawal amount must not be greater than the balance)

3. the deposit method (deposit amount must not be negative)

Modify the code for the BankAccount class so that each of the three methods throws an IllegalArgumentException if the precondition is violated.

What is the code for your modified BankAccount class?

2. Write a tester program that asks the user for:

the initial balance an amount to deposit an amount to withdraw

Have the program construct a BankAccount object and make the deposit and withdrawal.

What is your tester program?

3. What happens when you make the following errors?

a. Construct an account with a negative balance b. Withdraw more money than the account balance

c. Enter an illegal input (such as "ten" instead of "10")

Custom Exceptions

4. It is often a good idea to define your own exception class rather than rely on a predefined class.

Define a class BankAccountException that can be used by the BankAccount class.

Your exception should be an unchecked exception.

What is the code for your exception class?

5. Why does it make sense to define the BankAccountException class as an unchecked exception class?

6. Now modify the BankAccount class to throw BankAccountException objects instead of IllegalArgumentException objects.

What is the code for your modified class?

7. If the BankAccountException class had been a checked exception, then what changes would you need to make

a. in the definition of the exception class?

b. in the BankAccount methods?

Propagating Checked Exceptions

8. The DateFormat class of the standard Java library has a method

Date parse(String source)

that converts a string such as

"2/27/05 8:00 AM"

into an object of type Date:DateFormat formatter = DateFormat.getDateTimeInstance( DateFormat.SHORT, DateFormat.SHORT); String source = . . .; Date d = formatter.parse(source);

If the source string is not in the correct format, then the parse method throws a ParseException, which is a checked exception.

In this exercise, you will implement a class Appointment that stores the date and description of an appointment:public class Appointment {    . . .    public String toString()    {       return "Appointment[date="             + formatter.format(date)             + "description=" + description + "; "             + "]";    }

   private Date date;    private String description;    private static DateFormat formatter = DateFormat.getDateTimeInstance(          DateFormat.SHORT, DateFormat.SHORT); }

Supply a constructor

Appointment(String aDate, String aDescription)

that constructs an Appointment object from two strings. If the first string is not in a legal format, your constructor should throw a ParseException.

9. Now you will create a class AppointmentBook that keeps an array list of appointments. Part of the class has been provided for you:

import java.util.ArrayList; import java.text.ParseException;

public class AppointmentBook {    public AppointmentBook()    {       book = new ArrayList<Appointment>();    }    . . .

   public void addAll(ArrayList<Appointment> list)    {       book.addAll(list);    }    public int getNumAppointments()    {       return book.size();    }    public Appointment getAppointment(int i)    {       return book.get(i);

   }

   public String toString()    {       String out = "";       for (Appointment a : book)       {          out = out + a.toString() + "\n";       }       return out;    }    private ArrayList<Appointment> book; }

Add a method add, that adds a new appointment to the book. The method should not catch the ParseException, but propagate it to the calling method.

public void add(String aDate, String aDescription)

Catching Exceptions

10. Write a program AppointmentBookTester whose main method asks the user to enter a series of appointments. Add the appointments into an appointment book object. If a parse error occurs in the add method, have the program instruct the user to reenter the appointment.

Here is an outline of the main method, which does not yet catch any exceptions.boolean done = false; while (!done) {    System.out.println("Next date (or -1 when done):");    String input1 = in.nextLine();    if (input1.equals("-1"))

   done = true;    else    {       System.out.println("Description:");       String input2 = in.nextLine();       book.add(input1, input2);    } } System.out.println(book);

Add the appropriate try/catch block and test your program.

What is the complete code for your AppointmentBookTester class?

11. The preceding program is tedious to use because the user must type all appointment data on the command-line. Improve the method so that the data can be stored in a file.

Put the data in a text file, say, appts.txt, and then provide this file name when the programs asks you to.

Create an AppointmentBookReader class that will read appointments stored in a file. Use the following class:

import java.util.Scanner; import java.text.ParseException; import java.io.FileReader; import java.io.IOException;

public class AppointmentBookReader {    public AppointmentBookReader()    {       book = new AppointmentBook();    }

   public AppointmentBook read(String filename)          throws IOException, ParseException    {       FileReader reader = new FileReader(filename);       Scanner in = new Scanner(reader);       while (in.hasNextLine())       {          String input1 = in.nextLine();          String input2 = in.nextLine();          book.add(input1, input2);       }      reader.close();       return book;    }

   private AppointmentBook book; }

To read from an appointment book, use the following code:

AppointmentBookReader bookReader = new AppointmentBookReader(); AppointmentBook book = bookReader.read(filename); System.out.println(book);

Now change the AppointmentBookTester program so that it uses an AppointmentBookReader.

If there is any exception, describe the nature of the exception in English. Print the contents of the appointment book at the end of your program, whether or not there is any exception.

What is the complete code for your AppointmentBookTester class?

12. Give an example of an input file that causes the AppointmentBookReader to throw a ParseException.

13. Give an example of an input file that causes the AppointmentBookReader to throw an NoSuchElementException.

The finally Clause

14. When there is an input error and the AppointmentBookReader class exits with an exception, it should close its FileReader object by calling reader.close().

Modify the read method of the AppointmentBookReader class to close reader in a finally clause.

What is the code for your modified read method?

Big Java / Java Concepts Lab 16Reading and Writing Text Files

1. Write a program to store multiple memos in a file. Allow a user to enter a topic and the text of a memo (the text of the memo is stored as a single line and thus cannot contain a return character). Store the topic, the date stamp of the memo, and the memo message.

Use a text editor to view the contents of the "memo.dat" file and to check that the information is stored correctly.

Creating a java.util.Date object with no arguments will initialize the Date object to the current time and date. A date stamp is obtained by calling the Date.toString() method.

Part of the code of the program has been provided for you:import . . . public class MemoPadCreator {    public static void main(String args[])    {       Date now;       Scanner console = new Scanner(System.in);       System.out.print("Output file: ");    String filename = console.nextLine();       try       {          PrintWriter out = . . .;          boolean done = false;          while (!done)          {             System.out.println("Memo topic (enter -1 to end):");             String topic = console.nextLine();             if (topic.equals("-1"))             done = true;             else             {                System.out.println("Memo text:");                String message = console.nextLine();                /** Create the new date object and obtain a dateStamp */                out.println(topic + "\n" + dateStamp + "\n" + message);             }          }          /** Close the output file*/       }       catch (. . .)       {       . . .       }    } }What is the code for your program?

2. Modify your memo writing program to read multiple memos stored in a text file. Memos are stored in three lines. The first line is the memo topic, the second line is the date stamp, and the third line is the memo message. Display the memos one at a time, and allow the user to choose to view the next memo (if there is one).

Part of the program code has been provided for you:

. . .

public class MemoPadReader {    public static void main(String[] args)    {       Scanner console = new Scanner(System.in);       System.out.print("Input file: ");       String inputFileName = console.nextLine();       try       {          FileReader reader = . . .;          Scanner in = new Scanner(reader);

         boolean done = false;          while (in.hasNextLine() && !done)          {             String topic = . . .;             String dateStamp = . . .;             String message = . . .;             System.out.println(topic + "\n" + dateStamp + "\n" + message);             if (. . .) // You should only ask to display the next memo if there are more memos in the file             {                System.out.println("Do you want to read the next memo (y/n)?");                String ans = console.nextLine();                if (ans.equalsIgnoreCase("n"))                done = true;             }          }

         reader.close();       }       catch (. . .)       {          . . .       }    } }

What is the code for your program?

3. Modify your simple memo reader program. Use the JFileChooser to allow the user to choose the file from which the memos will be read.

You can use the showOpenDialog method to enable the user to select a file to "open". This method returns either JFileChooser.APPROVE_OPTION, if the user has chosen a file, or JFileChooser.CANCEL_OPTION, if the user canceled the selection.

If a file was chosen, then you call the getSelectedFile method to obtain a File object that describes the file. Here is a complete example:JFileChooser chooser = new JFileChooser(); FileReader in = null; if (chooser.showOpenDialog(null) == JFileChooser.APPROVE_OPTION) {    File selectedFile = chooser.getSelectedFile();    reader = new FileReader(selectedFile);    . . . }

What is the code for your program?

File Encryption

4. Write a program that encrypts (or decrypts) a file using an XOR cipher. An XOR cipher encrypts a byte by performing an XOR bitwise operation with the byte to be encrypted and a key. In Java, you can perform bitwise XOR using the ^ operator.

First, write a class XorEncryptor that encrypts or decrypts a file using an XOR cipher. Part of the code of the class has been provided for you:import . . .

/**    An encryptor encrypts files using a "XOR" cipher. */ public class XorEncryptor {    /**       Constructs an encryptor.       @param aKey the encryption key    */    public XorEncryptor(byte aKey)    {       key = aKey;    }

   /**       Encrypts the contents of a file.       @param inFile the input file       @param outFile the output file    */    public void encryptFile(String inFile, String outFile)       throws . . .    {       InputStream in = null;       OutputStream out = null;

      try       {          in = . . .;          out = . . .;          encryptStream(in, out);       }       finally       {          /** Close the files */       }    }

   /**       Encrypts the contents of a stream.       @param in the input stream       @param out the output stream    */    public void encryptStream(InputStream in, OutputStream out)       throws . . .    {       boolean done = false;       while (!done)       {          int next = . . .;         if (next == -1) done = true;          else

         {             byte b = (byte) next;             byte c = encrypt(b);             out.write(c);          }       }    }

   /**       Encrypts a byte.       @param b the byte to encrypt       @return the encrypted byte    */    public byte encrypt(byte b)    {       return . . .;    }

   private byte key; }

What is the complete code for the XorEncryptor class?

5. Write a tester program that asks the user for the name of a file to encrypt (or decrypt) and the name of the output file, and encrypts (or decrypts) the file. Note that both operations are performed in exactly the same way. Your program should also ask the user for the encryption key to use.

What is the complete code for your tester class?

6. Test your program. Create a file with the following content and encrypt it. Use "a" as the encryption key.

This is a test for the XOR encryptor.

Open the encrypted file with a text editor. What are the contents of the encrypted file?

7. Decrypt the file you just encrypted using your program. Don't forget to use "a" as the decryption key. What is the output?

Command Line Arguments

8. Modify your testing program so that the input file, output file, and encryption key are supplied on the command line.

What is the code for your modified tester class?

9. What command do you use to run your program to encrypt the file message.txt into the file message.enc, using a as the encryption key? What command do you use to decrypt the message.enc file?

Random Access Files

10. Create a program that reads and stores memos in a RandomAccessFile. To be able to read and write memos in a random access file, the topic, date stamp and message should each have a fixed size.

First, complete the code for the class MemoPad. You will write the tester program in the next problem.

public class MemoPad {    public MemoPad()    {       file = null;    }    public void open(String filename) throws IOException    {       . . .    }    /**       Gets the number of memos in the file.       @return the number of memos    */    public int size() throws IOException    {       . . .    }    public void close() throws IOException    {       if (file != null) file.close();       file = null;    }

   /**       Reads a memo record. The values of the last record read can be obtained       with the getTopic, getDateStamp and getMessage methods.       @param n the index of the memo in the file    */    public void read(int n) throws IOException    {       file.seek(. . .);       byte[] topic = new byte[MAX_CHARS_TOPIC];       byte[] date = new byte[MAX_CHARS_DATE];       byte[] message = new byte[MAX_CHARS_MSG];       /* Read the topic, date and message from the file (use the method "read(byte[])".          Then, convert the byte arrays to strings and store them in the variables currentTopic,          currentDateStamp and currentMessage       */    }    public String getTopic()    {       return currentTopic; // returns the topic of the last memo read    }

   public String getDateStamp()    {

      return currentDateStamp;     

public String getDateStamp()    {       return currentDateStamp;    }

   public String getMessage()    {       return currentMessage;    }

   public void write(int n, String topic, String dateStamp, String message) throws IOException    {       file.seek(. . .);       file.writeBytes(. . .); // "topic" should have a fixed size       file.writeBytes(. . .); // "dateStamp" should have a fixed size       file.writeBytes(. . .); // "message" should have a fixed size    }    /**       Adds white spaces to a string or cuts the string, so the string has a length of exactly "size".       @param str the input string       @param size the desired size       @return the new string    */    private String padOrTrim(String str, int size)    {       if (str.length() < size)       {          String pad = "";          for (int i = str.length(); i < size; i++)          pad = pad + " ";          return str + pad;       }       else          return str.substring(0, size);    }    private RandomAccessFile file;    private String currentTopic;    private String currentDateStamp;    private String currentMessage;

   public static final int MAX_CHARS_TOPIC = 25;    public static final int MAX_CHARS_DATE = 40;    public static final int MAX_CHARS_MSG = 250;    public static final int RECORD_SIZE = MAX_CHARS_TOPIC + MAX_CHARS_DATE       + MAX_CHARS_MSG; }

What is the complete code for this class?

11. Write a tester program that allows the user to add or display a memo. Memos should be added to the end of the file. If the user wants to display a memo, a list of the existing topics should be provided, so that the user can select which one he/she wants to see. Complete the following program:

public class MemoPadTester {    public static void main(String args[])    {       Scanner console = new Scanner(System.in);       System.out.println("Input file:");       String filename = console.nextLine();       try       {         MemoPad memoPad = new MemoPad();          memoPad.open(. . .);          boolean done = false;          while (!done)          {             System.out.print("Enter A to add a memo, D to display an existing memo or Q to quit: ");             String choice = console.nextLine();             if (choice.equalsIgnoreCase("A"))            {                System.out.println("Topic (max 25 characters):");               String topic = console.nextLine();                String dateStamp = (new Date()).toString();                System.out.println("Message (max 250 characters):");

               String message = console.nextLine();                memoPad.write(. . ., topic, dateStamp, message);             }             else if (choice.equalsIgnoreCase("D"))             {                if (memoPad.size() > 0)                {                   // Display the list of topics                  for (int i = 0; i < . . .; i++)                   {                      memoPad.read(. . .);                      System.out.println(i + " " + . . .);                   }

                  System.out.println("Enter the number of the memo to display:");                   int n = Integer.parseInt(console.nextLine());                   memoPad.read(. . .);                   System.out.println(. . .); // topic                   System.out.println(. . .); // date stamp                  System.out.println(. . .); // message                }                else                {                   System.out.println("There are no memos in the file.");                }             }             else if (choice.equalsIgnoreCase("Q"))

               done = true;          

}          memoPad.close();       }       catch (IOException exception)       {          System.out.println("Input/output error: " + exception);       }    } }

What is the complete code for this class?

Object Streams

12. Write a program that writes memos to a file as object streams.The Memo class should have fields to store a topic, a date stamp and the memo message. Allow a user to enter multiple memos, supplying the topic and message. Your program should provide the date stamp using the java.util.Date object. (Creating a Date object with no arguments initializes the object to the current time and date).

Let the user choose the file name to which the memos are saved.

What is the code for your Memo class? Remember to implement the Serializable interface!

13. Provide a tester program for your Memo class. Allow a user to enter multiple memos, supplying the topic and message. Your program should provide the date stamp using the java.util.Date object (creating a Date object with no arguments initializes the object to the current time and date). Let the user choose the file name to which the memos are saved.

After saving the file, your tester program should open the file and print out all memos.

You can modify the program you created in problem 1.

What is the code for your tester program?

Big Java / Java Concepts Lab 17Discovering Classes

1. You have been given an assignment to write a program to schedule classrooms in your college's building. Classrooms can be reserved for classes, seminars, guest speakers, and for meetings for clubs (such as the Java Users Group). Clubs can meet only after 5 p.m. and only if the room is not needed by any other group. Each group needing a classroom is given a priority. Classes in your college have the highest priority, with clubs having the lowest priority. Some classes in your college have higher priority over others, especially if the instructor has tenure. Classrooms are characterized by size, amenities (overhead projectors, etc.) and comfortable seats. Groups can specifically request a room by room number or simply give a description of what they need. Groups also may request specific time slots or give a range of acceptable time slots. Rooms are not available after 10 p.m. and before 5 a.m.

Make a list of classes that you may need for your program.

2. From your list of potential classes in your classroom-scheduling program, pick three potential classes and identify their main responsibilities.

3. A CRC card describes a class, its responsibilities, and its collaborating classes. You already identified the classes and responsibilities in the classroom-scheduling program. Now you will identify the collaborating classes.

From your list of potential classes in your classroom-scheduling program, pick three potential classes and identify their collaborators.

Relationships Between Classes

4. Using the list of classes for your classroom-scheduling program, identify any objects that may use inheritance. List the superclasses (if any) followed by their subclasses. If you see no need for inheritance, explain.

5. Inheritance can be described as an "is-a" relationship between classes. Aggregation can be described as a "has-a" relationship. Identify any aggregation relations in the classroom scheduling problem.

6. Identify the relationships between classes in the following code:class GroceryBag extends BasicContainer {     private Fruit[] fruits;     private Vegetable[] veggies;

. . .

    public void addItem(Food item)     {        . . .     }

    public Money computeTotal()     {        . . .     }

    . . . }

Inheritance

From which classes does GroceryBag inherit?

Aggregation

Identify any aggregation relationships (has-a relationship).

Dependency

On which classes does GroceryBag depend (uses relationship)?

Case Study

7. In this case study, you will develop a program to be used for ordering from an online pizza restaurant. Allow the user the following choices: pizza size (small, medium, or large), pizza crust type (thin or thick), pizza toppings, as well as small, medium, and large drinks. The user may select specific toppings. A user can order multiple pizzas and drinks. The order should include the customer's delivery address. After taking the order, print an order slip that shows the order information and total price.

Each topping has a price (for example, onions $1 and pepperoni $2). The price of a pizza is the sum of the base price ($10 for a small pizza, $13 for a medium, and $16 for a large pizza), plus the sum of the topping prices. The crust type doesn't affect the price.

The price of a drink is the base price of the drink ($1 for soda, $2 for beer) multiplied by a size factor (0.8 for small, 1.0 for medium, 1.2 for large drinks).

The delivery charge is $3. It is waived for pickup orders.

What classes can you identify using the "nouns from the requirements specification" technique?

8. Not all of the classes are immediately visible in the requirements specification. In our example, a pizza and a drink have common properties:

the price the description that is printed on the order slip

In fact, if the restaurant were to start serving other items (such as bread sticks or sandwiches), those items also would have a price and a description.

Define a suitable class that captures this commonality, and indicate how the classes Pizza and Drink are related to this class.

9. What are the responsibilities and collaborators of the Order class? 

10. You probably decided you need a class Topping. What is the code for your Topping class? If you think you do not need a class Topping, explain why.

11. A very important class in your program is probably going to be called Pizza. What is the code for your Pizza class. If you think you need superclasses and/or subclasses of Pizza, supply the code for these classes too.

12. Supply the code for your Drink class.

13. An order should contain a list of items (pizzas or drinks), so that the total price can be calculated and the order can be formatted to be printed. Supply the code for your Order class here.

14. Supply the code of any other classes you need to complete your program.

Big Java / Java Concepts Lab 18Recursion

1. The factorial of a positive integer is the product of all nonnegative integers less than or equal to that number. (The symbol for factorial is "!" - the exclamation mark.)

The formula for factorials for all nonnegative integers is:

n! = n * (n-1)! for n > 0;

Zero factorial is a special case and 0! = 1

From this definition, 5! is 120:1! = 1 * 0! = 12! = 2 * 1! = 23! = 3 * 2! = 64! = 4 * 3! = 245! = 5 * 4! = 120

Write a recursive factorial method long factorial(int n)

2. You can also compute the factorial values iteratively, without using recursion. Supply a non-recursive factorial method.

3. Write a tester class that tests both solutions.

4. A formula for finding the greatest common divisor (GCD) of two numbers was formulated by the mathematician Euclid around 300 BCE. The GCD of two numbers is the largest number that will divide into both numbers without any remainder. For example, the GCD of 12 and 16 is 4, the GCD of 18 and 12 is 6.

The basic algorithm is as follows:

Let a be the larger, b the smaller number. (We will assume that both values are positive.)

Let c be the remainder that is obtained after dividing a through b.

If c is zero, then the GCD is b.

Otherwise, the GCD of a and b is the same as the GCD of b and c.

Recall that in Java, the % operator computes the remainder. For example, to compute the GCD of 12 and 16, you compute16 % 12 = 4Now you need to compute the GCD of 12 and 4. 12 % 4 = 0Therefore, the GCD is 4.

Write a recursive method that finds the GCD of two numbers using Euclid's algorithm. (You may assume--or, better, assert--that both inputs are positive.)

5. Write a tester program for your GCD class.

Recursive Helper Methods

6. Write a program to draw the logarithmic spiral recursively.

The logarithmic spiral or Fibonacci spiral is a shape often found in nature. The nautilus shell is the classic example of the logarithmic spiral. Seed patterns in sunflowers and pinecones also demonstrate the spiral.

To construct a logarithmic spiral, begin with a "golden" rectangle. A golden rectangle is a rectangle with sides of length A and φA, where φ (Phi) is the golden mean or the value ( 1 + sqrt(5) ) / 2 or 1.61803 . . . A square with length equal to the smallest side of the rectangle is drawn inside the rectangle. A quarter arc (arcAngle = 90 degrees) is drawn within this square. The remaining rectangle is also a golden rectangle. This remaining rectangle is divided into a square and another smaller golden rectangle. A quarter arc connected to the previous arc is drawn inside the square, and the remaining rectangle is once again subdivided with an arc drawn in it.

Create a panel in which to draw the spiral:

public class LogSpiralPanel extends JPanel 

Given the dimensions of the panel, draw the largest golden rectangle that will fit within the panel. Part of the code of the class has been provided for you:

import java.awt.Graphics2D; import java.awt.Graphics; import java.awt.Rectangle; import java.awt.geom.Arc2D; import javax.swing.JPanel;

public class LogSpiralPanel extends JPanel {

   public void paintComponent(Graphics g)    {

Graphics2D g2 = (Graphics2D) g;        /*         Your code goes here.          1. create the goldenRectangle (you can use getHeight() to obtain the side size          2. draw the golden rectangle          3. call the recursive helper method "recursiveDraw" which will draw the spiral        */    }    /**       Method that recursively draws a logarithmic spiral.       @param x The upper left corner x-coordinate of the golden rectangle       @param y The upper left corner y-coordinate of the golden rectangle       @param side the smallest side size of the golden rectangle       @param angle the angle (0, 90, 180 or 270) where the top of the golden rectangle is located.       For the outermost golden rectangle, the angle is 90. */     private void recursiveDraw(Graphics2D g2, double x, double y, double side, int angle)     {        // we'll do this in the next section. . .     }          private static final double GOLDEN_MEAN = (1 + Math.sqrt(5)) / 2; }

What is the code of your completed paintComponent method?

7. Now you will complete the code of the recursive helper method recursiveDraw. To recursively draw the logarithmic spiral, you first need to draw the square. The square's upper-left corner is at position (x, y), and its side size is side. Then you need to draw the arc. You can use the method drawArc that has been provided for you. Then you need to recursively call recursiveDraw to continue drawing the spiral recursively. Before making the recursive call you need to calculate the new side size, the new x-coordinate, the new y-coordinate and the new angle. Two methods calculateNewX and calculateNewY have been provided for you. You can use these methods to calculate the new x and y coordinate, but you need to calculate the new side size and the new angle yourself. Remember that the new side size is the difference between the sizes of the two sides of the current rectangle. The new angle is given by rotating the current angle 90 degrees in clock-wise direction.

public class LogSpiralPanel extends JPanel {     public void paintComponent(Graphics g)     {     . . .     }

    /**         Method that recursively draws a logarithmic spiral.         @param x The upper left corner x-coordinate of the golden rectangle         @param y The upper left corder y-coordinate of the golden rectangle         @param side the smallest side size of the golden rectangle         @param angle The angle (0, 90, 180 or 270) where the top of the         current golden rectangle is located.         For the outermost golden rectangle, the angle is 90.      */     private void recursiveDraw(Graphics2D g2, double x, double y, double side, int angle)     {         /* Recursion ending condition: when the side is very small */         . . .

        /* Draw the current square and arc */         . . .

        /* Continue drawing the spiral recursively: calculate the new side size, calculate the new             (x, y) coordinates and the new angle. Then, call "recursiveDraw" again. */         . . .     }     /**         Draws the arc of the current iteration.         @param x The upper-left corner x-coordinate of the square         @param y The upper-left corner y-coordinate of the square         @param side The size of the side of the square (or the arc's radius)         @param angle The angle (0, 90, 180 or 270) where the top of

the current golden rectangle is located.         For the outermost golden rectangle, the angle is 90.

*/     private void drawArc(Graphics2D g2, double x, double y, double side, int angle)     {         double auxX = x;         double auxY = y;         if (angle == 0 || angle == 270)             auxX = x - side;         if (angle == 270 || angle == 180)             auxY = y - side;         Rectangle2D.Double boundingRectangle = new Rectangle2D.Double(auxX, auxY, side * 2, side * 2);         Arc2D.Double arc = new Arc2D.Double(boundingRectangle, angle, 90, Arc2D.OPEN);         g2.draw(arc);     }

    private double calculateNewX(double x, double angle, double side, double newSide)     {         if (angle == 0)             x = x + side - newSide;         else if (angle == 90)             x = x + side;         else if (angle == 270)             x = x - newSide;         return x;     }

    private double calculateNewY(double y, double angle, double side, double newSide)     {         if (angle == 0)             y = y + side;         else if (angle == 180)             y = y - newSide;         else if (angle == 270)             y = y + side - newSide;         return y;     }

    private static final double GOLDEN_MEAN = (1 + Math.sqrt(5)) / 2; }

What is the code of your recursiveDraw method?

8. Create a LogSpiralFrame class that will contain the LogSpiralPanel. What is the code of your class?

9. What is the code of your viewer class?

The Efficiency of Recursion

10. The golden mean, often referred to as the golden ratio, divine proportion, or the golden number is represented by the Greek letter phi (φ). The value of the golden mean is (1 + sqrt(5)) / 2 or 1.61803 . . . The golden mean is found in nature and art and tends to yield the most "aesthetically pleasing" arrangements of objects.

Fibonacci numbers are directly related to the golden mean. The definition of Fibonacci numbers is

fib(1) = 1

fib(2) = 1

fib(n) = (fib(n-1) + fib(n-2))

After the first two numbers, each of which has the value of 1, the next number in the Fibonacci sequence is the sum of the two preceding numbers.

Computing ratios of Fibonacci numbers can approximate the value of the golden mean. The value of.

g(n) = fib(n) / fib(n-1)

approximates the golden mean as n goes to infinity.

These values can be computed recursively as well. Note thatg(n) = (fib(n - 1) + fib(n - 2)) / fib (n - 1)Simplify this expression so that g(n) is expressed in terms of g(n - 1).

(a) What is your recursive definition for g(n)? (b) When does the recursion stop?

11. Write a recursive method that computes the nth iteration of the golden ratio. What is the code of your method?

12. What is the tenth approximation of the golden ratio?

13. As you learned in the textbook, the recursive computation of fib(n) can be inefficient. Add trace statements to verify that your method for computing g(n) does not calculate each number more than once. What is the output of your trace messages?

Mutual Recursion (and More Efficiency)

14. In one variant of the game of Nim, two players alternately take marbles from a pile. In each move, a player chooses how many marbles to take. The player must take at least one but at most half of the marbles. Then the other player takes a turn. The player who is left with one marble loses.

Clearly, if you start with two marbles, you are going to win. Take one marble, and your opponent loses right away. We therefore say that 2 is a winning position.

In general, a winning position is a position in which you can force a win. That is, there is at least one move that leads to a losing position.

Conversely, a losing position is a position that is either an outright loss, or in which every move leads to a winning position.

Following these definitions, write mutually recursive methods

public class NimCalculator{   public boolean isWinningPosition(int n)    {       for (int i = 1; i <= n / 2; i++)         . . .

   }   public boolean isLosingPosition(int n) { . . . }}

What is the code for your methods?

15. Run a test program.Which values between 2 and 100 are losing positions?

16. Why does this recursion run so slowly? Add trace messages to find out.

17. You can speed up the methods by remembering for which numbers you have already determined the answers. Use an array to store known positions.

public class NimCalculator{   public boolean isWinningPosition(int n) { . . . }   public boolean isLosingPosition(int n) { . . . }   private int[] knownPositions = new int[10000];

}

Here, knownPosition[i] should be 1 if i is known to be a winning position, and -1 if i is known to be a losing position, and 0 if it is not known to be either.

What is the code for your modified isWinningPosition and isLosingPosition methods?

18. Now run your program again. Just print out the losing positions < 10000

Big Java / Java Concepts Lab 19Sorting

1. Add a counter to the MergeSorter that counts how many times the algorithm compares two array elements. Supply a method getCounter to retrieve the counter. Then run the following experiment. For n = 10000, 20000, . . ., 100000, prepare an array with descending integer values n, n - 1, n - 2, . . .,3, 2, 1. Pass it to the MergeSorter, then print out how many comparisons were made.

What results did you get?

2. Implement the bubble sort algorithm.

The bubble sort is so called because it compares adjacent items, "bubbling" the smaller one up toward the beginning of the list. By comparing all pairs of adjacent items starting at the end of the list, the smallest item is guaranteed to reach the beginning of the list at the end of the first pass.

The second pass begins again at the end of the list, ultimately placing the second smallest item in the second position in the list. During the second pass, there is no need to compare the first and second items, since the smallest element is guaranteed to be in the first position.

Bubble sort takes at most n-1 passes for a list of n items. During the first pass, n-1 pairs need to be compared. During the second pass, n-2 pairs need to be compared. During the ith pass, n-i pairs need to be compared. During the last pass, n-(n-1) or one pair needs to be compared. If, during any pass, no two adjacent items need to be interchanged, the list is in order and the sort can terminate. If it continues, no further interchanges will occur.

A variation on the bubble sort starts each pass at the beginning of the list, interchanging items as needed so that a larger item "sinks" below a smaller item following each comparison. Such a sort might be called a "rock sort," but this term is not in common usage.

What is the code of your BubbleSorter class?

3. Describe the efficiency of the bubble sort algorithm and represent it in Big-Oh notation.

4. A variation on the bubble sort starts each pass at the beginning of the list, interchanging items as needed so that a larger item "sinks" below a smaller item following each comparison. (Such a sort might be called a "rock sort," but this term is not in common usage.)

Implement this variation. What is the code for your sort method?

Comparable and Comparator

5. We want to sort a list of cities by name; however, if there are two cities with the same name, then we use the state name as tie breaker. Implement a City class and a constructor

public City(String name, String state)

Also supply a toString method--we will need it for testing.

Have your City object implement the Comparable<City> interface.

What is the code of your City class?

6. Write a tester class that populates an ArrayList<City> with cities and then sorts it. What is the code of your tester class? Remember that you can use Collections.sort to sort an array list.

7. Now we want to sort lists of cities first by state name, then by city name, without modifying the implementation of the City class. That means, you cannot redefine the compareTo method. Instead, define a CityComparator class that implements the Comparator<City> interface.public class CityComparator implements Comparator<City> {     public int compare(City a, City b)     {        . . .     } }

What is the code of your CityComparator class?

8. Write a tester class that populates an ArrayList<City> with cities and then sorts it, using a CityComparator. What is the code of your tester class? 

Binary Search

9. We will implement a "guess your name" game. The computer will guess your last name:This program tries to guess your last name, but you have to give some hints.Does your name come before "MYERSCOUGH" in the dictionary? (Y/N) YDoes your name come before "ISENBERG" in the dictionary? (Y/N) YDoes your name come before "DIMAGGIO" in the dictionary? (Y/N) NDoes your name come before "GALLUP" in the dictionary? (Y/N) N

. . .Is your name "HORSTMANN"? (Y/N) Y

Start out with a program that reads all names from the "last names" file at http://www.census.gov/genealogy/names/. Discard the statistical information. Sort the names, using Collections.sort.

What is the code for reading all names and sorting them?

10. At the beginning of the search,  set low to 0 and high to the maximum index of the names list. Set mid to the average of low and high, then ask the user if the name comes before the list entry at index mid. Depending on the answer, update low or high. If low == high, ask if the name matches.

What is the code for your program?

11. How many entries does your names list have? How many guesses does your program need to make until it has guessed the user's name or given up?

Big Java / Java Concepts Lab 20Using Linked Lists

1. Using the "cursor in a word processor" notation from the book, indicate the contents of the list and the iterator position after each step in the code below. LinkedList<String> letters = new LinkedList<String>(); ListIterator<String> iterator = letters.listIterator(); iterator.add("A"); iterator.add("C"); iterator.add("D"); iterator = letters.listIterator(); iterator.next(); iterator.next(); iterator.remove();

Implementing Linked Lists

2. The LinkedList class in the standard Java library has a get(int index) method that allows you to retrieve arbitrary list elements, just like you can in an ArrayList. In this lab, we want to analyze why this operation is inefficient.

Add a methodObject get(int index)

to the LinkedList implementation of Chapter 20. What is the code for your method?

3. What does your method do if index is < 0 or >= the size of the linked list?

4. Write a tester program that adds ten items to a LinkedList and then executes the loop

for (int i = 0; i < list.size(); i++)   System.out.println(list.get(i));

What is the code for your tester program?

5. How many times does the tester program look up the next value of a list node? How many lookups would it make if there were 100 elements in the list?

6. It is possible to optimize the behavior of the get method in some common cases. You can cache the last visited position and its Node pointer. Then you can start from that position instead of the start of the linked list. public Object get(int index){ Node current; if (lastVisitedPosition > 0 && lastVisitedPosition < index) { current = lastVisitedNode; while (. . .) current = current.next; } else { current = first; while (. . .) current = current.next; } // remember for next time lastVisitedPosition = index; lastVisitedNode = current; . . .}

Finish the implementation of the method, and test it with the same tester program.

What is the code of the get method?

7. With this modification, how many times does the tester program look up the next value of a list node?

8. This is an ingenious trick, but it has limitations. If another method mutates the linked list, then the cached position may no longer be accurate, and the cache should be invalidated by setting lastVisitedPosition to -1. Which methods of the LinkedList and LinkedListIterator class need to be modified?

9. The standard library does not use this trick in its implementation of get, but it uses another optimization: if index is > size() / 2, then the search starts at the end of the list, not at the beginning. With that optimization, how many lookups of the next or previous value would the tester program make if it looped through a list with 100 elements?

Abstract and Concrete Data Types

10. You are assigned to write a program to schedule appointments for a doctor's office. An appointment is scheduled every half an hour from 8 a.m. to 4 p.m., with no appointments between 12 p.m. and 1 p.m. Not all times may be scheduled, and some times may be double-booked. You must be able to delete and add appointments at anytime. Would you use a linked list or an array to store appointments? Why?

11. When performing a binary search, is it more appropriate to use an array or a linked list? Why?

Stacks and Queues

12. A deque is a double-ended stack or a double-ended queue. Items can be inserted or removed from either end. Write an implementation of a deque of strings using a LinkedList. No other type of element access should be permitted (e.g. get element at position i).public class Deque {     . . .     public void addFirst(Object str){ . . . }     public Object removeFirst(){ . . . }     public void addLast(Object str){ . . . }     public Object removeLast(){ . . . }     private LinkedList<Object> list;}

13. Suppose you make your previous deque implementation iterable by modifying it as follows:

public class Deque implements Iterable<Object> {   . . .

    public Iterator<Object> iterator()     {        return list.iterator();     }

    private LinkedList<Object> list; }

Now you can iterate through the deque using the "for each" loop. Adding this functionality is very useful because it allows us to iterate through the elements of the queue and print them.

Write a test program that adds elements to a deque and then prints them out with a "for each" loop. What is your test program?

14. The problem is that by returning an iterator, we would be allowing an illegal operation to the deque: to be able remove an element at an arbitrary position, by calling iterator.remove().

Write a tester program that shows that if you change your queue implementation as suggested above, you can now remove an element in the middle of the list.

15. You can solve the problem by disabling the remove() method for your Deque iterator You can do that by creating your own iterator class which just calls the methods of the list iterator, except for the remove method. If another class calls the iterator's remove method, the method should not perform the remove operation; instead, it should throw an UnsupportedOperationException.

Part of the code of the class has been provided for you:public class Deque implements Iterable<Object> {

    public Iterator<Object> iterator() { return new DequeIterator(); }

    private class DequeIterator implements Iterator<Object>     {         public DequeIterator() { . . . }         public boolean hasNext() { . . . }         public Object next() { . . . }         public void remove() { . . . }

        private Iterator<Object> iterator;     }     . . .}

What is the code of your modified ListQueue class?

16. Use the tester program you created in problem 14. What happens when you try to remove an element using the iterator's remove()?

17. A couple has a monthly surplus of $300 that is set aside in an account for discretionary spending. The account balance was $0 in January. In April, the couple decided to purchase a new couch that cost $1600. In May they decided to purchase a weaving loom that cost $2000. In August, they decided to purchase a laptop computer for $1,100. In September, they decided to purchase a trip to Italy for $4,000. In December, they decided to purchase a season pass for the local cross-country ski resort for $200. 

Items are purchased when there is money available. Unpurchased items remain in the queue until sufficient funds become available. This way, the items are purchased in the order that they are requested.

Write a program to simulate the spending and savings of this couple. Allow a user to enter the amount of discretionary money that is set aside each month. Also allow the user to enter items to be purchased each month.

What is the code for your program?

18. With the data from the preceding problem,    1. What is the largest surplus accumulated in the special account for discretionary spending?   2. What is the largest deficiency for items for which there are insufficient funds?

Modify your program to supply this information and give the results.

Big Java / Java Concepts Lab 21Sets and Maps

1. Consider the following line of code:

Set names = new HashSet();

Why is the variable names of type Set rather than type HashSet?

2. Unlike the ListIterator interface, the Iterator interface for a set cannot add an item to a specified position. Is there a reason for this? If so, what is it?

3. The Iterator interface contains a next method. Why does the interface not contain a previous method?

4. For each of the following problems, indicate whether it would be more appropriate to use a HashSet or a HashMap, and explain your reasoning:

1. A program that keeps track of bank account information (name, account number, account type, balance)

2. A phonebook program that stores your friends' names and phone numbers

3. A program to inventory the contents of your refrigerator

4. A program that stores a list of your favorite fruits

5. A program that stores a list of the favorite fruits of all the students in your class.

5. Suppose you write a program to keep track of the hometowns of all the students in your class using a HashMap. What values would you use for the key set? What values would you use for the value set?

6. The static method TimeZone.getAvailableIDs returns an array of time zone ID strings, such as America/Los_Angeles or Asia/Bankgok. Once you have an ID, you can get the time zone by calling the static method TimeZone.getTimezone. Finally, to find the time at a given time zone, callDateFormat timeFormatter = DateFormat.getTimeInstance();

timeFormatter.setTimeZone(zone);

Date now = new Date();

System.out.println(timeFormatter.format(now));

Unfortunately, there is no fast method for finding the time zone for "Los_Angeles". We want to speed up this search by using a Map<String, TimeZone>.

Write a program that calls getAvailableIDs, strips out the city names (by discarding the Continent/ prefix and turning underscores into spaces), gets the TimeZone objects, and puts the (city name, time zone) pairs into a map.

To verify that your map is set up correctly, print out the first ten entries.

What is the code for your program?

7. What does your program print?

8. Now enhance your program so that users can enter city names. Look up the time zone for the city and print out the local time, or tell the user if you can't find a matching city.City: Los Angeles

Local time: 06:26:09

City: Berlin

Local time: 15:27:12

City: Fargo

Local time: not available

City: Quit

Bye

What is the code for your program?

Hashing

9. Create an Employee class. The class contains the id (of type long), name, phone number and job title of the employee. Implement the methods:

public boolean equals(Object other)

public int hashCode()

10. Write a test program that stores a set of employees in a HashSet<Employee> and prints out the elements in the set. Try adding the same employee twice. What is the code of your test program? 

11. How can you simplify the equals and hashCode methods if you know that employees are uniquely determined by their ID?

Binary Search Trees

12. Write a program that builds up the following binary search tree and prints its contents.

5

/ \

3 8

/ \ / \

1 4 6 10

\ \ /

2 7 9What is the code for your program?

13. In this exercise, we will add an iterator to the binary search tree class in the text book. We want to be able to execute code such asBinarySearchTree tree = new BinarySearchTree();

// add elements

Iterator iter = tree.iterator();

while (iter.hasNext())

do something with iter.next();

The iterator should visit the tree elements in sorted order.

Here is a naive attempt at the iterator:public class BinarySearchTree

{

. . .

public Iterator iterator() { return new BSTIterator(); }

private class BSTIterator implements Iterator

{

public BSTIterator() { current = root; }

public boolean hasNext() { return current != null; }

public Object next()

{

Object r = current.data;

if (current.left != null) current = current.left;

else current = current.right;

return r;

}

public void remove() { throw new UnsupportedOperationException(); }

private Node current;

}

}

Unfortunately, this simplistic approach won't work. Which elements will the iterator visit when it traverses the tree of problem 12?

14. The simplistic implementation can't back up when it reaches a leaf. Unfortunately, our Node objects don't have a pointer to the parent. Therefore, we need to store a stack of partially explored nodes. When reaching a leaf, pop off the top of the stack and continue the search at that node.

private class BSTIterator implements Iterator

{

. . .

private Node current;

private Stack<Node> partiallyExplored;

}

Draw pictures of the state of this iterator for each traversal step in the tree of problem 11.

13. Now implement the iterator class. What is the code for your implementation?

14. Add an iterator to the program that you wrote in problem 12. What is the code for your test program?

Tree Sets

15. Write a program that uses a tree set to store employees. Ask the user to enter employee information, add each employee to the three set. When the user is done, print the elements of the tree set. You can modify the program you created in problem 10.

16. Run both implementations of the program (the one that uses a hash set and the one that uses a tree set) and insert information about the employees Brown, Smith and Johnson (in that order). What is the output of both programs?

Heaps

17. A min-heap is an almost complete tree in which the values of all nodes are at most as large as those of their descendants. A max-heap is the opposite of a min-heap. The largest element is stored in the root of a max-heap.

Turn the MinHeap class in the book into a MaxHeap class. What is the code?

18. Write a tester class that tests your MaxHeap.

What is the code?

19. For convenience, the MinHeap and MaxHeap class leave the 0 element of the array empty. Then the child nodes of the node with index i have index 2 · i and 2 · i + 1 , and the parent node of the node with index i has index i / 2.

Change your implementation so that the 0 entry is not wasted. (Hint: Look at the HeapSorter class of your text book.)  Run your test program again to verify that your changed implementation works correctly.

What changes did you need to make?

Big Java / Java Concepts Lab 22Implementing Generic Classes

1. Modify the class Pair<T, S> so that it implements Comparable<Pair<T, S>>. To compare a pair with another, you compare the first element (using compareTo). If they are equal, you should compare the second elements and return the result of their comparison. If the first elements are not equal, the compareTo method returns the result of first.compareTo(other.first).

2. Create a PairTester class that tests the class you just created. Create a new TreeSet and add pairs to it. The pairs should consist of people names (last name, first name). At the end, iterate through the set and print its contents. If your Pair class was correctly implemented, the output should be displayed in alphabetic order (because a TreeSet implements a set using a binary search tree). Be sure to try a few pairs with the same last name.

3. What happens if you try to add a Pair<String, Integer> to the set? What happens if your try to create a Pair<String, Rectangle>? Try it out and explain.

4. Turn the MinHeap class in Section 21.9 of your textbook into a generic class. The bound of the type variable should extend the generic Comparable interface:public class MinHeap<E extends Comparable>

You need not understand the inner workings of the MinHeap class in order to carry out this exercise. Simply change methods such as public Comparable peek()intopublic E peek()so that the user of the generic class need not apply any casts. Be sure to change the type of the elements instance field to ArrayList<E>.

What is the code for your modified class?

5. A heap (in this case, a min-heap) can be used as a priority queue. Modify the following program so that it uses your generic MinHeap class and it uses Pair<Integer, String> instead of the class WorkOrder.

/**    This program demonstrates the use of a heap as a priority queue.

*/ public class HeapTester {    public static void main(String[] args)    {       MinHeap q = new MinHeap();       q.add(new WorkOrder(3, "Shampoo carpets"));       q.add(new WorkOrder(7, "Empty trash"));       q.add(new WorkOrder(8, "Water plants"));       q.add(new WorkOrder(10, "Remove pencil sharpener shavings"));

      q.add(new WorkOrder(6, "Replace light bulb"));       q.add(new WorkOrder(1, "Fix broken sink"));       q.add(new WorkOrder(9, "Clean coffee maker"));       q.add(new WorkOrder(2, "Order cleaning supplies"));

      while (q.size() > 0)          System.out.println(q.remove());    } }

6. In the previous exercise, could you have replaced the WorkOrder class with Pair<String, Integer>? (e.g. q.add(new Pair<String, Integer>("Shampoo carpets", 3));). Explain your answer.

Generic Methods

7. Add a generic getRandomElement method to the ArrayUtil class of your textbook that returns a random element from an array of type E[].

(Use a static random number generator, and generate a random integer between 0 and a.length - 1.)

What is the code for your generic method?

8. Add a generic getRandomPair method to the ArrayUtil class. It should return a randomly chosen pair, with the first index less than the second index. For example, if called with the array ["A" "B" "C" "D"], then a pair ("A", "B"), ("A", "C"), ("A", "D"), ("B", "C"), ("B", "D"), ("C", "D") is chosen with equal probability.

What is the code for your generic method?

10. Write a tester class that tests the static methods you created. What is the code for your tester class?

Constraining Type Variables

11. In the ArrayUtil class, write generic methods

void saveToFile(E[] a, String filename) throws IOExceptionE[] loadFromFile(String filename) throws IOException, ClassNotFoundException

The first method saves the elements of the given array to an ObjectOutputStream. The second method loads an array of objects from an ObjectInputStream.

When writing the type variable of the method, you should take into consideration that the elements of the array must implement the Serializable interface.

12. Write a tester program for your previous class. Create an array of strings and add several strings to it. Save the list to a file, afterwards read them from the file and display them on screen.

13. What happens if you don't supply the Serializable bound for the elements of the array list?

First change your tester program so that the elements of the array are of type Pair<String, String>. Try it out and explain.

Then, change your class to remove the Serializable bound, use your modified tester program and try it out. Explain.

Overcoming Limitations of Java Generics

14. Generic classes and methods were added to Java several years after the language became successful. The language designers decided to use the type erasure mechanism because it makes it easy to interface generic code with legacy programs. As a result, you may run into some programming restrictions when you write generic code.

For example, you cannot construct an array of a generic type. The following method, which tries to grow an array, would be wrong:

public static <E> E[] grow(E[] a) {   E[] newArray = new E[2 * a.length + 1]; // ERROR    for (int i = 0; i < a.length; i++)       newArray[i] = a[i];    return newArray;}

To see why this is a problem, carry out the type erasure process, as if you were the compiler.

What would be the result?

15. A tempting workaround would be to create an array of objects, like this:

public static <E> E[] grow(E[] a) {   E[] newArray = (E[]) new Object[2 * a.length]; // ERROR

   for (int i = 0; i < a.length; i++)       newArray[i] = a[i];    return newArray;}

Try out this "solution". What happens when you callString[] original = {"Hello", "World"};String[] grown = ArrayUtil.grow(original);

16. To solve this problem, you need to find out the type of the array a and make a new array of the same type.

You can get the type of the components of a by calling Class cl = a.getClass().getComponentType();The object cl is a descriptor for the component type. For example, when a is a String[] array, then cl describes the String type.

Now use the newInstance method of the java.lang.reflect.Array class to make a new array of the type cl. You still need to cast the result as E[] (and you will still get a warning), but now you are no longer lying.

What is the code for your modified grow method?

17. Write a tester class for the grow method.

What is the code of your tester class?

Big Java Lab 23Running Threads

1. Write a program to simulate a simple traffic light at an intersection of two roads.

It will be easiest to view the example as four one-way roads, since cars can approach and pass through the intersection from four directions. Assign each road a number from 1 to 4.

Each time a car is at the intersection, request that the traffic light turn green. Implement a traffic light object with a turnGreen(int roadNumber) method. When a car is at the intersection it will call this method and pass its number. If road number 1 calls the turnGreen method, the method should print out:

Light turned green by road 1

Waiting for road 1 car to clear intersection

10 9 8 7 6 5 4 3 2 1 0

Use a loop to print a countdown of the waiting period from 10 to 0.

What is the code of your TrafficLight class.

Big Java Lab 24Sockets

1. Write a program that uses a socket to retrieve the correct time from a timeserver using the DAYTIME protocol.

There are many servers on the Internet that provide a time service. The National Institute of Standards and Technology http://www.bldrdoc.gov/ maintains several timeservers that allow users to synchronize a clock. One protocol used is the Daytime protocol. The Daytime protocol is a simple protocol. The user connects on port 13 and sends a newline character. The server responds by sending back an ASCII string and then disconnects. The time string from the NIST servers is in the following format:

JJJJJ YR-MO-DA HH:MM:SS TT L H msADV UTC(NIST) *

In this simple exercise, we are concerned only with the first half of the string.

JJJJJ represents the last five digits of the Julian date. You can ignore this value.

YR-MO-DA YR represents the last two digits of the year, MO represents the month and DA, the current day.

HH:MM:SS is the time in hours (HH), minutes (MM) and seconds (SS). This is sent in Coordinated Universal time.

You need to add an offset to correct the time to your time zone.

Write a program that connects to three of the NIST servers listed below, using the Daytime protocol. Parse the return string and create a Date object set to the return string's time. Print out the return strings and your Date objects. Use a SimpleDateFormat to format your date. Make sure you adjust the time to your correct time zone. You should read the Java API documentation to obtain more information on the SimpleDateFormat class. Basically you will need to use the class to parse the string (or substring of) returned by the server. For example, the following formatter is able to format a string of the form "05-02-25 17:30:49 UTP", by using its parse method:

SimpleDateFormat formatter = new SimpleDateFormat("yy-MM-dd HH:mm:ss z");

After obtaining a Date object using formatter.parse, you can format it to your local time using the format method of the DateFormat class:

DateFormat localFormatter = DateFormat.getDateTimeInstance();

NIST TimeserversName Location

time-a.nist.gov NIST, Gaithersburg, Maryland

time-b.nist.gov NIST, Gaithersburg, Maryland

time-a.timefreq.bldrdoc.gov NIST, Boulder, Colorado

time-b.timefreq.bldrdoc.gov NIST, Boulder, Colorado

time-c.timefreq.bldrdoc.gov NIST, Boulder, Colorado

utcnist.colorado.edu University of Colorado, Boulder

time.nist.gov NCAR, Boulder, Colorado

time-nw.nist.gov Microsoft, Redmond, Washington

nist1.datum.com Datum, San Jose, California

nist1.dc.glassey.com Abovenet, Virginia

nist1.ny.glassey.com Abovenet, New York City

nist1.sj.glassey.com Abovenet, San Jose, California

nist1.aol-ca.truetime.com TrueTime, AOL facility, Sunnyvale, California

nist1.aol-va.truetime.com TrueTime, AOL facility, Virginia

What is the code of your program?

2. Modify your previous program so that it uses the TIME protocol instead of the DAYTIME protocol. To use the Time protocol, a user connects on port 37 and sends a newline character. The server responds by returning a 32-bit unformatted binary number that represents the time in UTC seconds since January 1, 1900.

Hints:

Unlike the C language, Java does not have an unsigned data type to represent an unsigned 32-bit binary number. An int in Java represents a 32-bit signed binary number. Usually a larger type, in this case a long, is used to store an unsigned int. The time server sends four bytes that represent an unsigned int, which you will have to store in a long. Instead of using a scanner, you will need to read an array of bytes using the input stream directly:

byte[] b = new byte[4];

instream.read(b);

Then, you will need to convert the byte array to a long. You can use the following method for the purpose:public static final long unsignedIntToLong(byte[] b) {     long l = 0;     l |= b[0] & 0xFF;     l <<= 8;     l |= b[1] & 0xFF;     l <<= 8;     l |= b[2] & 0xFF;     l <<= 8;     l |= b[3] & 0xFF;     return l; }

Java stores dates as the number of milliseconds since January 1, 1970. The Time protocol returns the number of seconds since January 1, 1900. To compute the difference, create a GregorianCalendar object that represents 01/01/1970 and a GregorianCalendar object that represents 01/01/1900. Call getTimeInMillis() on each to retrieve the milliseconds. Then subtract to find the difference. Convert the difference to seconds and add it to the return value. Convert the corrected return value to milliseconds to create your Date object.

Client/Server

3. Create a server application that uses the following protocol:

Client Request Server Response Meaning

HELLO greeting Sends a greeting

ECHO n n Echoes n back to the client

COUNT The number of ECHO requests Returns a count of the number of ECHO requests by client

QUIT goodbye Prints a goodbye and quits the connection

You may choose the greeting and goodbye messages to send. In this exercise you will create three classes:

SimpleProtocolService

SimpleProtocolServer

SimpleProtocolClient

The server should accept multiple simultaneous connections with different clients.

What is the code of your SimpleProtocolService class? Part of the code of the class has been provided for you:public class SimpleProtocolService implements Runnable { public SimpleProtocolService(Socket aSocket) { . . . }

public void run() {        try        {           try           {              in = new Scanner(s.getInputStream());              out = new PrintWriter(s.getOutputStream());              doService();           }           finally           {              s.close();           }        }        catch (IOException exception)        {           exception.printStackTrace();        }     }     public void doService() throws IOException { . . . }

    public void executeCommand(String command) { . . . }     . . .

}

. . .

}

4. To support multiple simultaneous connections, construct a new thread to communicate with each client. What is the code of your SimpleProtocolServer class?

5. Write a client that connects to the server, sends several commands and disconnects. What is the code of your SimpleProtocolClient class?

URL Connections6. Write a program that gets a weather report for your state. The URL is

http://iwin.nws.noaa.gov/iwin/xy/hourly.html

where xy is a 2-letter state abbreviation such as ca or ny.

Your program should get the data from the web site and strip out all HTML formatting, printing just the raw weather report.

7. What is the output of your program if the URL points to an invalid location? (for example, http://iwin.nws.noaa.gov/iwin/ev/hourly.html)

Tic-tac-toe

8. In this section, we will create a server application that allows two players to play tic-tac-toe against each other.

Design and implement a protocol to play tic-tac-toe. A player can connect, give the player name, and wait for an opponent. When two opponents have connected, the server picks one of them to start

playing. The active player must be able to transmit a move to the server. The server checks

that the move is valid. If the last move finishes the game, the server pronounces the winner.

The server notifies both players of the new board position, and, if the game is not yet over, asks the opponent to play.

Simply number the rows and columns and communicate moves with the row and column numbers.

What are the client requests and server responses in your protocol?

9. What is the code of your TicTacToeServer class?

10. What is the code of your TicTacToeServer class?

11. What is the code of your TicTacToeClient class?

Big Java Lab 25SQL

1. Design a set of database tables for a pizza restaurant.

The restaurant stores the names, addresses, and phone numbers of its home delivery customers. All the current and previous orders for each customer are stored in the database. An order includes one or more pizzas. A pizza has size, crust type, one or more toppings.

The price of a pizza is the sum of the base price ($10 for a small pizza, $13 for a medium, and $16 for a large pizza), plus the sum of the topping prices. The crust type doesn't affect the price.

List the SQL code creating the tables.

2. Write SQL statements to populate your tables with data.

3. Give a SQL query that lists all pizza toppings for your pizza restaurant database.

4. Give an SQL query to find if there is a customer named 'John Smith' in the database.

Give an SQL query to find the customer code (or id) for the customer named 'John Smith'.

5. Give a SQL query that describes a particular order for a particular client, for example, order with order code '6' for client '1'.

6. How can you calculate the total of an order?

JDBC

7. Write a Java program to implement your pizza restaurant database.

The restaurant stores the names, addresses and phone numbers of its customers. All the current and previous orders for each customer are stored in the database. An order includes one or more pizzas. A pizza has size, crust type and one or more toppings.

The price of a pizza is the sum of the base price ($10 for a small pizza, $13 for a medium, and $16 for a large pizza), plus the sum of the topping prices. The crust type doesn't affect the price.

Using the tables you created and populated with data, write a PizzaOrderingSystem class with a method

public void acceptOrder()

that asks for the customer information and order, and stores the information in the database. You may additional helper classes.

What is the code of your PizzaOrderingSystem class?

8. Did you use helper classes? If so, what is their code?

9. What is the code of your tester program?

10. To run your program you need a database properties file. What is the content of your database.properties file?

11. You are the store manager and want to give a special prize to your best customer. Give an SQL query to find out what customer has the greatest number of orders in the system.

Big Java Lab 26Parsing XML Documents

1. Consider the following XML file that describes a pizza:<pizza>    <name>BBQ Chicken</name>    <description>       <crust>thin</crust>        <sauce>barbecue</sauce>       <cheese>Gouda</cheese>        <cheese>mozzarella</cheese>       <toppings>            <meat>chicken</meat>            <vegetable>red onion</vegetable>            <vegetable>cilantro</vegetable>       </toppings>    </description> </pizza>

Make a similar XML file that describes your favorite pizza.

2. Write a program that can read XML files for describing a pizza, in the format of the preceding exercise.

Read the information in the file and create an instance of a class Pizza and then display it on screen, including the total pizza price. You can use the Pizza class and helper classes that you created in lab 17.

What is the code of your parser class?

3. What is the code of your tester class?

4. Creating XML Documents

Write a program to create a pizza restaurant menu stored as an XML file. Read in several XML files describing pizzas, in the same format as before. Make a Menu object that contains an ArrayList<Item>. Each item contains a pizza and a price.

Your program should then produce an XML document with a <menu> root element describing the menu:<menu>    <item>      <pizza>           . . .       </pizza>       <price>...</price>   </item>   <item>      <pizza>           . . .       </pizza>    <price>...</price>   </item></menu>

What is the code of your builder class?

5. What is the code of your tester class?

Document Type Definitions (DTDs) 6. Design a document type definition (DTD) that describes a pizza.

Include a name and description, including crust type, toppings, and sauce.

7. Write a program that can read and validate XML files for describing a pizza.

Modify your existing program to read an XML file containing a pizza description, using a DTD for validation.

How does your parser class change?

8. What happens if you use the following as your pizza.xml file?

<?xml version="1.0"?> <!DOCTYPE pizza SYSTEM "pizza.dtd"> <pizza>    <name>BBQ Chicken</name>    <description>       <crust>thin</crust>       <size>medium</size>       <sauce>barbecue</sauce>       <cheese>gouda</cheese>       <cheese>mozzarella</cheese>       <toppings>          <topping>chicken</topping>          <topping>red onion</topping>          <topping>cilantro</topping>       </toppings>    </description>    <price currency="USD">16</price> </pizza>

Big Java Lab 27Warming Up

1. Create a JSF page that uses a bean to display a random number between 1000 and 9999. Use the following format:

Today's lucky number is 1729.

What is the code of your bean class?

2. What are the contents of your index.jsp file? Note: your file can have a different name.

3. What are the contents of your web.xml file?

4. What are the contents of your faces-config.xml file?

5. Describe the directory structure of your application.

A Simple JSF Program

6. Create a JSP page that uses a JavaBean to display a random "fortune."

Create a list of ten fortunes. When a user opens the page, display a random fortune.

Sample output:__________________________________________________

The Virtual Fortune CookieYour fortune: A short stranger will soon enter your life.__________________________________________________

What is the code of your bean class(es)?

7. What are the contents of your *.jsp file(s)?

Interacting with the User 8. Create a JSF page that allows a user to enter a category for the fortune that they want to

have displayed. Categories might include

Love Money Food Computers

The program displays a fortune that matches the category that the user selected. Sample output:__________________________________________________

The Virtual Fortune CookieYour fortune: That wasn't chicken you just ate.__________________________________________________

What is the code of your bean class(es)?

Error Checking and Navigation 10. Create a JSF page that allows a user to enter a category for the fortune that they want to

have displayed. Use a text field for the category.

If the user entered an unknown category, show an appropriate message. If the user entered a known category, show a fortune cookie. Both pages should have a "Back" button that returns to the original page.

What is the code of your bean class(es)?

11. What are the contents of your *.jsp file(s)?

12. In what file did you include your navigation rules? How did you define them?

Database Connectivity 13. For a more robust program, we want to store the fortunes and their categories in a

database.

Modify the bean code so that it looks up fortunes in a database table.

What is the code of your bean class(es)? (You should not modify the JSF pages.)

14. Give a SQL script that populates the database table. 

15. What error message do you get when a user connects to your JSF application when the database server is not running?