Java Programming Basics

Sang Shin, sang.shin@sun.com, Sun Microsystems, www.javapassion.com/javaintro


The goal of this hands-on lab is to get you exposed to the Java programming basics, such as how to declare and use variables, how to use conditional operators.


Expected duration: 100 minutes


Software Needed

Before you begin, you need to install the following software on your computer. 


Change Log



Lab Exercises


Exercise 1: Declare, Initialize, Print variables

In this exercise, you are going to learn how to declare, initialize a variable.  You also learn how to modify and display a value of a variable.

(1.1) Build and run OutputVariable Java program using "javac" compiler and "java"

1. Go to a directory where you are going to write Java programs

C:\>cd \myjavaprograms

2. Write OutputVariable.java using your editor of choice (in this example, I am using jedit) as shown in Code-1.10 below. 

C:\myjavaprograms>jedit OutputVariable.java

public class OutputVariable {

    public static void main( String[] args ){

        // Variable value is int primitive type and it is initialized to 10
        int value = 10;
    
        // Variable x is char primitive type and it is initialized to 'A'
        char x;
        x = 'A';
       
        // Display the value of variable "value" on the standard output device
        System.out.println( value );

        // Display the value of variable "x" on the standard output device
        System.out.println( "The value of x=" + x );

    }

}
Code-1.10: OutputVariable.java

3. Compile OutputVariable.java using javac compiler.  The javac compiler comes with J2SE SDK you've download.  It resides in %JAVA_HOME%\bin (Windows) or $JAVA_HOME/bin (Solaris/Linux) directory. The result of compilation will be the creation of OutputVariable.class file.

C:\myjavaprograms>javac OutputVariable.java

4. Run the OutputVariable program using java command. The java command starts the Java Virtual Machine and runs the OutputVariable program in this example.  A Java program can be made of multiple Java classes and and a set of libraries.  In this example, the OutputVariable program just contains a single class called OutputVariable.class. You can regard the java command as Java interpreter.

C:\myjavaprograms>java OutputVariable
10
The value of x=A


7. Modify OutputVariable.java as shown in Code-1.11 below.  You are modifying it to add double type variable called grade and displays the value of it.  The code fragments that need to be added are highlighted in bold and blue-colored font.

public class OutputVariable {

    public static void main( String[] args ){

        // Variable value is int primitive type and it is initialized to 10
        int value = 10;
    
        // Variable x is char primitive type and it is initialized to 'A'
        char x;
        x = 'A';

        // Variable grade is a double type
        double grade = 11;
       
        // Display the value of variable "value" on the standard output device
        System.out.println( value );

        // Display the value of variable "x" on the standard output device
        System.out.println( "The value of x=" + x );

        // Display the value of variable "grade" on the standard output device
        System.out.println( "The value of grade =" + grade );

    }

}
Code-1.11: Modified OutputVariable.java

8. Compile and run the program. Observe that new message is displayed.

C:\myjavaprograms>javac OutputVariable.java

C:\myjavaprograms>java OutputVariable
10
The value of x=A
The value of grade =11.0


                                                                                                                        return to top of the exercise

(1.2) Build and run OutputVariable Java program using NetBeans IDE


0. Start the NetBeans IDE if you have not done so.
1. Create a NetBeans project


Figure-1.20: Create OutVariable project

2. Modify the IDE generated OutputVariable.java.
/*
 * OutputVariable.java
 *
 * Created on January 19, 2007, 6:30 PM
 *
 * To change this template, choose Tools | Template Manager
 * and open the template in the editor.
 */

/**
 *
 * @author sang
 */
public class OutputVariable {
   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        // Variable value is int primitive type and it is initialized to 10
        int value = 10;
    
        // Variable x is char primitive type and it is initialized to 'A'
        char x;
        x = 'A';

        // Variable grade is a double type
        double grade = 11;
       
        // Display the value of variable "value" on the standard output device
        System.out.println( value );

        // Display the value of variable "x" on the standard output device
        System.out.println( "The value of x=" + x );

        // Display the value of variable "grade" on the standard output device
        System.out.println( "The value of grade =" + grade );
    }
   
}
Code-1.21: Modified OutputVariable.java


Figure-1.22: Modified OutputVariable.java

3. Build and run the program

Figure-1.23: Result of running OutputVariable program


Summary

In this exercise, you have built and run OutputVariable Java program using javac compiler and java command and NetBeans IDE.
   
                                                                                                                                   Return to the top


Exercise 2: Conditional operator

In this exercise, you are going to write a Java program which uses conditional operators.

  1. Build and run a Java program that uses conditional operators

(2.1) Build and run a Java program that uses conditional operators

1. Create a NetBeans project

2. Modify the IDE generated ConditionalOperator.java.
public class ConditionalOperator {
   
    /** Creates a new instance of ConditionalOperator */
    public ConditionalOperator() {
    }
   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {

        // Declare and initialize two variables, one String type variable
        // called status and the other int primitive type variable called
        // grade.
        String status = "";
        int grade = 80;

        // Get status of the student.
        status = (grade >= 60)?"Passed":"Fail";

        // Print status.
        System.out.println( status );
    }
   
}
Code-2.21: Modified ConditionalOperator.java

3. Build and run the program


Figure-2.22: Result of running the program

4.  Modify ConditionalOperator.java as adding the following lines of code at the appropriate place, build and run the program


Summary

In this exercise,  you have built and run a Java application using NetBeans IDE.


                                                                                                                        return to the top




Exercise 3: Averaging numbers

In this exercise, you are going to build and run a sample Java program in which an average of numbers are computed and displayed.

  1. Build and run a Java program

(3.1) Build and run a Java program

1. Create a NetBeans project

2. Modify the IDE generated AverageNumber.java.
public class AverageNumber {
   
    /** Creates a new instance of AverageNumber */
    public AverageNumber() {
    }
   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        //declares the three numbers
        int num1 = 10;
        int num2 = 20;
        int num3 = 45;
       
        //get the average of the three numbers
        // and saves it inside the ave variable
        int ave = (num1+num2+num3)/3;
       
        //prints the output on the screen
        System.out.println("number 1 = "+num1);
        System.out.println("number 2 = "+num2);
        System.out.println("number 3 = "+num3);
        System.out.println("Average is = "+ave);
    }
   
}
Code-3.11: Modified AverageNumber.java

3. Build and run the program


Figure-3.12: Result of running AverageNumber program

Exercise 4: Find greatest number

In this exercise, you are going to write a Java program which uses conditional operators.

  1. Build and run a Java program that uses conditional operators

(4.1) Build and run a Java program that uses conditional operators

1. Create a NetBeans project


Figure-4.10: Create MyGreatestValueProject
2. Modify the IDE generated GreatestValue.java.
public class GreatestValue {
   
    /** Creates a new instance of GreatestValue */
    public GreatestValue() {
    }
   
    /**
     * @param args the command line arguments
     */
    public static void main(String[] args) {
        //declares the numbers
        int num1 = 10;
        int num2 = 23;
        int num3 = 5;
        int max = 0;
       
        //determines the highest number
        max = (num1>num2)?num1:num2;
        max = (max>num3)?max:num3;
       
        //prints the output on the screen
        System.out.println("number 1 = "+num1);
        System.out.println("number 2 = "+num2);
        System.out.println("number 3 = "+num3);
        System.out.println("The highest number is = "+max);
    }
   
}
Code-4.11: Modified GreatestValue.java

3. Build and run the program


Figure-4.12: Result of running MyGreatestValueProject


Homework exercise (for people who are taking Sang Shin's "Java Programming online course")


1. The homework is to modify the MyGreatestValueProject project above.   (You might want to create a new project by copying the MyGreatestValueProject project.)  You can name the new project in any way you want but here I am going to call to call it as MyGreatestValueProject2. 
2. Send the following files to javaprogramminghomework@sun.com with Subject as JavaIntro-javaprogbasics.