A Short Program with a variable

A variable is a memory location that may be assigned a value. The value of a variable is changeable.

The following code defines a variable and change its value by assigning a new value to it.


public class Example {
  public static void main(String args[]) {
    int num; // a variable called num
    num = 100;

    System.out.println("This is num: " + num);
    num = num * 2;

    System.out.print("The value of num * 2 is ");
    System.out.println(num);
  }
}

When you run this program, you will see the following output: 


This is num: 100 

The value of num * 2 is 200

The following snippet declares an integer variable called num. Java requires that variables must be declared before they can be used. 


int num; // this declares a variable called num

Following is the general form of a variable declaration: 


type var-name;

In the program, the line assigns to num the value 100.


num = 100; // this assigns num the value 100

Define more than one variable with comma

To declare more than one variable of the specified type, you may use a comma-separated list of variable names.


public class Example {
  public static void main(String args[]) {
    int num, num2;
    num = 100; // assigns num the value 100
    num2 = 200;
    System.out.println("This is num: " + num);
    System.out.println("This is num2: " + num2);

  }
}

When the program is run, the following output is displayed: 


This is num: 100
This is num2: 200

Using Blocks of Code

Java can group two or more statements into blocks of code. Code block is enclosing the statements between opening and closing curly braces({}).

For example, a block can be a target for Java's if and for statements. Consider this if statement: 

  
public class Main {
    public static void main(String args[]) {
        int x, y;
        x = 10;
        y = 20;
        if (x < y) { // begin a block
            x = y;
            y = 0;
            System.out.println("x=" + x);
            System.out.println("y=" + y);
        } // end of block
    }
}

Here is the output of the code above: 


x=20
y=0

A block of code as the target of a for loop. 

 

public class Main {
  public static void main(String args[]) {
    int i, y;
    y = 20;
    for (i = 0; i < 10; i++) { // the target of this loop is a block
      System.out.println("This is i: " + i);
      System.out.println("This is y: " + y);
      y = y - 1;

    }
  }
}

The output generated by this program is shown here: 


This is i: 0
This is y: 20
This is i: 1
This is y: 19
This is i: 2
This is y: 18
This is i: 3
This is y: 17
This is i: 4
This is y: 16
This is i: 5
This is y: 15
This is i: 6
This is y: 14
This is i: 7
This is y: 13
This is i: 8
This is y: 12
This is i: 9
This is y: 11
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First Java Program:
  1. Create your first Java program
  2. A Short Program with a variable