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Java while Loop



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The while loop is the most fundamental loop statement of Java. It repeats a statement or block while its controlling expression is true. Here is the general form of while loop in Java:

while(condition)
{
	// body of the loop
}

The condition can be any Boolean expression. The body of the loop will be executed as long as the conditional expression is true. When the condition becomes false, the control passes to the next line of code immediately following the loop. The curly braces are unnecessary if only a single statement is being repeated.

Java while Loop Example

Following is a while loop that counts down from 10, printing exactly 10 lines of "tick" :

/* Java Program Example - Java while Loop
 * Demonstrate the while Loop */

public class JavaProgram
{   
    public static void main(String args[])
    {
        
        int n = 10;
        
        while(n>0)
        {
            System.out.println("tick " + n);
            n--;
        }
        
    }
}

When the above Java program is compile and executed, it will produce the following output:

java while loop

Since the while loop evaluates its conditional expression at the top of the loop, the body of the loop will not execute even once if the condition is false to begin with. For example, in the following code fragment, the call to println() is never executed:

int a = 10, b = 20;
while(a > b)
{
	System.out.println("This will not be displayed.");
}

The body of the while loop can be empty. This is because a null statement (once that consists only of a semicolon) is syntactically valid in Java. For example, consider the following program:

/* Java Program Example - Java while Loop
 * The target of a loop can be empty */

public class JavaProgram
{   
    public static void main(String args[])
    {
        
        int i, j;
        
        i = 100;
        j = 200;
        
        // find midpoint between i and j
        while(++i < --j);    // there is no body in this loop
        
        System.out.println("Midpoint is " + i);
        
    }
}

When the above Java program is compile and executed, it will produce the following output:

while loop in java

Example Explained

The value of i is incremented, and the value of j is decremented. These values are then compared with one another. If the new value of i is still less than the new value of j, then the loop repeats. If i is equal to or greater than j, the loop stops. Upon exit from the loop, i will hold a value that is midway between the original values of i and j. (Of course, this procedure only works when i is less than j to begin with.) As you can see, there is no need for a loop body, all of the action occurs within the conditional expression, itself. In professionally written Java code, short loops are frequently coded without bodies when the controlling expression can handle all of the details itself.

More Examples

Here are the list of some more examples, that you may like:


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