csi 1390: introduction to computers ta: tapu kumar ghose office: ste 5014 email:...
TRANSCRIPT
Create Folders and text files
Creating folder Navigate to the directory where the folder is to be
created Click right button of the mouse Point the mouse over the “New” item of the menu Click on the “Folder” option of the sub-menu Give a name to the newly created folder Press F2 to rename the folder name
Create Folders and text files Creating text file using “notepad”
Click the “start” menu presented at the bottom-left corner of the window
Point the mouse over the “All Programs” item Point the mouse over the “Accessories” item of the sub-menu Click on the “Notepad” application of the sub-menu Click on the “File” from the menu bar of the notepad Using the “Save in” drop down list, navigate to the directory/folder
where the text file is to be saved or created Give a name to the newly created text file by entering a name in the
“File name” box. Click “Save” to save the file By default the extension of the file is “.txt” Press F2 to rename the file name
Using command promt to access the folders Click the “start” menu presented at the bottom-left corner of the
window Point the mouse over the “All Programs” item Point the mouse over the “Accessories” item of the sub-menu Click on the “Command Promt” to open the command promt The above three steps can be done by clicking “Run…” from the start”
menu and entering “cmd” in the text box. Suppose we want to access the “Program Files” folder of the C
directory. We can do so by entering as follows:
cd\ cd Program Files (going into the “Program Files” folder) dir (viewing the content of the folder)
Now, using the above procedure go to the folder that you created
First Program: Hello World Open a notepad to write a java program that will display “Hello World” as
output. The program is as follows:
class myProgram {public static void main (String args[]){ System.out.println(“Hello world.”);}
} The “bin” directory of java is located at C:\Program Files\Java\jdk1.5.0_12\
bin Save the file into the above directory by giving the file name same as the
class name of the java program that we wrote Here, the file name will be “myProgram.java”. Note that the file extension
is java. To make the file as a java file, choose “All files” from the Save as Types
drop down box at the time of saving. Failure to do will make the file as a normal text file with .txt extension.
Compile and run the program The “bin” directory of java is located at C:\Program Files\Java\
jdk1.5.0_12\bin Go to the above directory by using command promt by using the
following steps: Open command promt and enter the following commands cd\ cd Program Files\Java\jdk1.5.0_12\bin
To compile the java program enter the following command javac myProgram.java
To run the java program enter the following command java myProgram
Explanation of the source codeclass myProgram {
public static void main (String args[]){ System.out.println(“Hello world.”);}
} Java program structured as a set of classes All Java code must be part of a “class” All classes must have a name. Here, our class name is “myProgram” Beginning of a class is identified by a opening brace { Ending of a class is identified by a closing brace } In a class there will be two things
attributes (store some information) methods (perform some specific task)
Explanation of the source codeclass myProgram {
public static void main (String args[]){ System.out.println(“Hello world.”);}
} Here we have only one method The name of the method is “main” “main” is a special name. All java program contains a method with the name “main” When any java program is run, it starts from the “main” method Body of each method contains set of statements Each statement is terminated by semi-solon (;) Here we have only one statement which prints the information between
the quotes.
Taking input from user Write a java program that will ask user to enter his/her name and age.
The purpose of the program is to display the user name and the square of his/her age.
Before starting writing the source code we always try to determine few things What would be the input(s) to the program? What would be the output(s) to the program? How would we calculate the output?
Here, the input is a string (for containing the name) and an integer (for containing the age).
Outputs are string (that contains the name) and integer (that contains the square of the age).
The output of age will be calculated by using the “pow” method of the “Math” class.
Source code with explanationimport java.io.*;import java.util.*;
class myProgram {public static void main(String[] args) throws IOException{
String name;int age;
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
System.out.print("Enter your name: ");
name = br.readLine(); System.out.println("Your name is " + name);
System.out.print("Enter your age: ");age = Integer.parseInt(br.readLine());
System.out.println(Math.pow(age,2));}
}
Source code with explanation
throws IOException: An exception that is thrown when I/O error encountered.
public static void main(String[] args) throws IOException
InputStreamReader works as a bridge from byte stream to character stream
It reads bytes and decodes into characters BufferedReader reads text from character input stream
BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
Alernative sotution Add the following codes just before the last brace } of the Keyboard.java file
public static void main(String[] args){
String name;int age;
Keyboard kb = new Keyboard();
System.out.print("Enter your name: ");
name = kb.readString(); System.out.println("Your name is " + name);
System.out.print("Enter your age: ");age = kb.readInt();
System.out.println(Math.pow(age,2)); // add [import java.util.8;] before the class definition}
}
Assignment Modify or add codes to the Keyboard.java file to do the following
assignments. Take the temperature of a day from the user in degree Celsius and
convert it into degree Fahrenheit by using the formula F = 9/5 * C + 32
Given the value of r and h, find the volume of a cylinder by using the formula V = pi * r * r * h (the value of pi can be obtained by using the Math class)
Due before 8 am on September 28, 2007