A loop statement allows us to execute a block of code or statement or group of statements as many times according to the user’s need. It is done by evaluating a given condition for true and false. The statement stops looping when the condition is false.
There are two types of loops :
1. Entry control loop: In this loop, the conditional is checked then the program is executed. There are two types of entry control loop.
- for loop.
- while loop.
2. Entry control loop: In this loop, the program is executed first and then the condition is checked. There is only one type of loop in the exit control loop.
- do-while loop.
1. while loop:
The while loop is one of the fundamental loop statement in Java. It is an entry-control loop, that is it checks the condition at the beginning of the block. And repeats a statement or block until the condition is true. And the increment of the variable checked in condition checking is done inside the block as shown in the below example.
Syntax of while loop:
1 2 3 4 | while(condition) { //block of code to be executed } |
Example: Click here
2. do…while loop:
Sometimes it is necessary that the block or statement must be executed at least once but if the condition is initially at a false state then the block will not be executed. So for the situation where a block of code must be executed at least once a do-while loop comes in play.
do-while is an exit-control loop that is it checks the condition after the first execution of the block. And it keeps executing the block until the condition state is false.
Syntax of do..while loop:
1 2 3 4 | do { statements.. }while (condition); |
Example: Click here
3. for loop:
The Java for loop allows the user to iterate a part of the program multiple times. If a user is certain about how many specific numbers of times the loop must be executed then for loop is recommended. It is also an entry-control loop but here flow control contains three steps:
- initialization = The first step is the initialization of the variable and is executed only once. And need to end with a semicolon(;).
- condition = Second is condition check, it checks for a boolean expression. If true then enter the block and if false exit the loop. And need to end with a semicolon(;).
- Increment or Decrement = The third one is increment or decrement of the variable for the next iteration. Here, we need to use the semicolon(;).
Syntax of for loop:
1 2 3 4 | for(initialization; condition; Increment or Decrement) { // Statements } |
Example: Click here
4. Enhanced For loop:
Java 5 added another version of for loop. It is useful to iterate through the elements of a collection or array.
Syntax of enhanced for loop:
1 2 3 4 | for(declaration : expression) { // Statements } |
Declaration – This is declared variable and must be compatible with the elements of collection or array that is executing. And is available only for that block.
Expression – This is the name of an array you need to loop through.
Example of enhanced for loop in Java:
1 2 3 4 5 6 7 8 9 10 11 12 13 | public class ForEachTest { public static void main(String args[]) { int num[] = {5, 10, 15, 20, 25, 30}; for(int a : num ) { System.out.println( a ); System.out.println("\n"); } } } |
Output:
1 2 3 4 5 6 | 5 10 15 20 25 30 |
Another example enhanced loop in Java with String:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 | public class ForEachTest { public static void main(String args[]) { String name[] = {"John", "Sam", "Arya", "Brandon"}; for( String singer : name ) { System.out.print( singer ); System.out.print("\n"); } } } |
Output:
1 2 3 4 | John Sam Arya Brandon |