practice final

CS280 Object-Oriented Programming-Fall12 Final Exam Practice Problems

Problem 1. Short answer problems. 1. What is displayed on the console when the following program is run?

public class Test { public static void main(String[] args) { try { System.out.println("Welcome to Java"); int[] a = new int[10]; a[10] = 1; System.out.println("Welcome to HTML"); } catch (Exception ex) { System.out.println("There is an exception); } System.out.println("Bye."); } }

2. ____________ sets a background of a JPanel object p to yellow.

a. p.setColor(Color.yellow) b. p.setBackground(Color.yellow) c. p.setBackgroundColor(Color.yellow) d. p.setBackGroundColor(Color.yellow)

3. _______________ draws a circle centered at position is (400, 400) with radius 50.

e. g.drawCircle(350, 350, 100, 100) f. g.drawOval(350, 350, 100, 100) g. g.drawCircle(400, 400, 50, 50) h. g.drawOvale(400, 400, 50, 50)

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4. Assume class B extends class C and implements interface A. What will be printed by

the following program?

public class Test { public static void main(String[] args) { B b = new B(); if (b instanceof A) System.out.println("b is an instance of A"); if (b instanceof C) System.out.println("b is an instance of C"); } }

5. The class Test below compiles without error, however, method max that is defined in

it can sometimes generate a run-time error. Explain a. Why the cast of o1 to Comparable is necessary for this code to compile without

error.

b. When and why a call to method max would result in a run-time error.

public class Test { public static Object max(Object o1, Object o2) { if omparable)o1).compareTo(o2) >= 0) ( ((C return o1; else return o2; } }

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Problem 2. The questions that follow are based on the definitions of classes Team and TournamentHistory below. These classes represent details of team performance in a tournament. Review these class definitions to answer the questions that follow. /* Class Team represents a Teams result in a particular year */ public class Team { private String name; private int year; // year of participation private int place; public Team (String name, int year, int place){ this.name = name; this.year = year; this.place = place; } public String toString (){ return this.name + " took " + this.place + " in " + this.year; } public String getName(){return this.name;} public int getYear(){return this.year;} public int getPlace(){return this.place;} } /* Class TournamentHistory represents a set of team results for a tournament. */ import java.util.ArrayList; public class TournamentHistory { private String name; private ArrayList teamData = new ArrayList(5);

public TournamentHistory (String tournamentName){

this.name = tournamentName; } public void addTeamRecord ( String name, int year, int place ){ boolean found = false; for (int i = 0; i< teamData.size()&&found == false; i++){ Team tm = teamData.get(i); if ( tm.getName().equalsIgnoreCase(name) && tm.getYear() == year) found = true; }

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if (found == true) System.out.println ("Record of team " + name + " for year " + year + " exists."); else { Team teamRec = new Team (name, year, place); teamData.add(teamRec); System.out.println (" Added " + teamRec); } } public static void main (String [] args ){ TournamentHistory fifaWC = new TournamentHistory ("FIFA World Cup"); fifaWC.addTeamRecord("West Germany", 1974, 1); fifaWC.addTeamRecord("Poland", 1974, 3); fifaWC.addTeamRecord("Poland", 1974, 4); fifaWC.addTeamRecord("West Germany", 1982, 2); } } a) What will be printed when the main method in the TournamentHistory class is

executed? Note that there are 2 printing statements; both are in method addTeamRecord of the TournamentHistory class. Show the output in the space provided below.

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b) In the space provided below, redefine the constructor of the Team class to throw an exception of type Exception in the following cases

1. The name parameter is null or is equal to an empty string. In such case throw an exception with message Team name cannot be blank.

2. The year parameter is


c) When the Team constructor is redefined to throw an exception as requested in part b), the following code segment from method addTeamRecord of the TournamentHistory class would not compile due to a potential exception:

// this code is from method addTeamRecord

if (found) System.out.println ("Record of team " + name + " for year " + year + " exists."); else { Team teamRec = new Team (name, year, place); teamData.add(teamRec); System.out.println (" Added " + teamRec); }

Rewrite the code above to handle the exception thrown by the Team constructor, so that when an exception is caught, the exceptions message is displayed to the user and nothing is added to the teamData arraylist.

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d) Complete the definition of a static method readFromFile below of the TournamentHistory class to create and return an object of type TournamentHistory, filled with data from file named data.txt that has the following format (illustrated in the box below):

1. The first line contains the name of the tournament 2. The rest of lines contain team data, including year, team name and the place number:

Sample file data.txt:

FIFA World Cup 1998 Croatia 3 1998 France 1 1998 Brazil 2 2002 Brazil 1

HINT: Use methods of the Scanner class to read data from the file, // this is part of class TournamentHistory public static TournamentHistory readFromFile(){ TournamentHistory th; // variable to store the object // that this method will create and // return.

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return th; }

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Problem 3. GUI with Swing (25 points)

The code displayed on the next page, when run, displays the following window. Answer the questions that follow.

a) The GUI is designed in such a way that the user cannot enter a value into the grayed area underneath the Canadian Dollars. Which line of code is responsible for ensuring this (write down your answer here).

b) What will happen when a user presses on the Exit button?

c) Which method is being invoked by the call super("Currency converter");

and what does that method do?

d) Make modifications to the program on the next page so that the it works as follows:

a. When the Exit button is pressed, the program terminates. b. When the Convert button is pressed, if there is nothing in the first text

field, a message should be displayed to the user to enter the US dollar amount. Otherwise (in case the US dollar amount is specified), the amount of Canadian dollars corresponding to the US Dollar amount specified in the first text field should be computed and displayed in the second text field.

You do not have to implement any exception handling for this problem.

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import javax.swing.*; import java.awt.*; public class TestActionEvent extends JFrame { private final double exchangeRate = 1.02; // 1 Canadian is worth 1.02 US private JTextField usValue = new JTextField(10); private JTextField caValue = new JTextField(10); private JButton bConvert = new JButton("Convert"); private JButton bExit = new JButton("Exit"); n/**Mai method*/ public static void main(String[] args) { TestActionEvent frame = new TestActionEvent(); } public TestActionEvent() { super("Currency converter"); // Use FlowLayout manager to arrange the components Container contentPane = this.getContentPane(); contentPane.setLayout(new FlowLayout()); // Add labels and text fields JLabel us = new JLabel ("US Dollars"); JLabel canadian = new JLabel ("Canadian Dollars"); contentPane.add(us); contentPane.add(usValue); contentPane.add(canadian); contentPane.add(caValue); caValue.setEditable(false); // Add buttons contentPane.add(bConvert); contentPane.add(bExit); this.setSize(200, 150); this.setVisible(true); }

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}

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