Loops In Java

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A while loop statement in java programming language repeatedly executes a target statement as long as a given condition is true.

Syntax:

The syntax of a while loop is:

while(Boolean_expression)
{
   //Statements
}

Here, statement(s) may be a single statement or a block of statements. The condition may be any expression, and true is any non zero value.

When executing, if the boolean_expression result is true, then the actions inside the loop will be executed. This will continue as long as the expression result is true.

When the condition becomes false, program control passes to the line immediately following the loop

Here, key point of the while loop is that the loop might not ever run. When the expression is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed.

Example:

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class Test {    public static void main(String args[]) {       int x = 10;       while( x < 20 ) {          System.out.print("value of x : " + x );          x++;          System.out.print("\n");       }    } }

This would produce the following result:

value of x : 10
value of x : 11
value of x : 12
value of x : 13
value of x : 14
value of x : 15
value of x : 16
value of x : 17
value of x : 18
value of x : 19

Decision making structures have one or more conditions to be evaluated or tested by the program, along with a statement or statements that are to be executed if the condition is determined to be true, and optionally, other statements to be executed if the condition is determined to be false.

Following is the general form of a typical decision making structure found in most of the programming languages:

Java programming language provides following types of decision making statements. Click the following links to check their detail.

Statement	Description
if statement	An if statement consists of a boolean expression followed by one or more statements.
if...else statement	An if statement can be followed by an optional else statement, which executes when the boolean expression is false.
nested if statements	You can use one if or else if statement inside another if or else if statement(s).
switch statement	A switch statement allows a variable to be tested for equality against a list of values.

The ? : Operator:

We have covered conditional operator ? : in previous chapter which can be used to replace if...else statements. It has the following general form:

Exp1 ? Exp2 : Exp3;

Where Exp1, Exp2, and Exp3 are expressions. Notice the use and placement of the colon.

To determine the value of whole expression, initially exp1 is evaluated

• If the value of exp1 is true, then the value of Exp2 will be the value of the whole expression.
• If the value of exp1 is false, then Exp3 is evaluated and its value becomes the value of the entire expression.

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class Dowhile {   public static void main(String[] args) {     int x = 0;     do {       ++x;       System.out.println(x);       if (++x < 5)         continue;       ++x;       System.out.println(x);     } while (++x < 10);   } }

package com.cv.java.loops; import java.util.ArrayList; import java.util.List; /**  * @author Chandra Vardhan  *   */ public class ForLoopEvenOddExample {   public static void main(String[] args) {     int[] n = { 1, 2, 3, 4, 5 };     List<Integer> list = new ArrayList<Integer>();     System.out.print("Odd numbers:");     for (int i = 0; i <= n.length - 1; i++) {       if (n[i] % 2 == 0) {         System.out.print(n[i] + " ");       } else {         list.add(n[i]);       }     }     System.out.println();     System.out.print("Even numbers:");     System.out.println(list);   } }

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class LabledForLoop {   public static void main(String[] args) {     l1: for (int i = 0; i < 3; i++) {       for (int j = 0; j < 3; j++) {         if (i == j)           continue l1;         System.out.println(i + "......." + j);       }     }   } }

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class MultiForLoop {   public static void main(String[] args)  {     for (int i = 0; i < 5; i++) {       for (int j = 5; j >= i; j--) {         System.out.println(i + "......." + j);       }     }   } }

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class While {   public static void main(String[] args) {     while (true) {       System.out.println("Hello");       break;     }     System.out.println("Hi");   } }

package com.cv.java.loops; /**  * @author Chandra Vardhan  *   */ public class WhileWithBreak {   public static void main(String[] args) {     for (int i = 0; i < 10; i++) {       System.out.println("The no of inside loop " + i);       boolean problem = true;       while (true) {         if (problem) {           System.out.println("there was a problem");           break;         }       }     }   } }