Java Loops

Loops

• In programming language, loops are used to execute a set of instruction or functions repeatedly when some conditions become true.
• Loops can execute a block of code as long as specified condition is reached.
• Loops are handy because they save time, reduce errors, and they make code more readable.

There are three types of loops in Java.

1.     while loop

2.     do-while loop

3.     for loop

Java While Loop

The Java while loop is used to iterate a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop.

Syntax:

while(condition){  
//code to be executed  
}  

 Flow diagram

Here, key point of the while loop is that the loop might not ever run. When the condition 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:

int i = 0;
while (i < 5) {
     system.out.println(i);
     i++;
}

 

Note: Do not forget to increase the variable used in the condition, otherwise the loop will never end!!

 

public class WhileExample {  
public static void main(String[] args) {  
    int i=1;  
    while(i<=10){  
        System.out.println(i);  
    i++;  
    }  
 }  
}  

Output:

1
2
3
4
5
6
7
8
9
10

Java Infinitive While Loop

If you pass true in the while loop, it will be infinitive while loop.

Syntax:

while(true) {  
//code to be executed  
}  

Example:

public class WhileExample2{  
public static void main(String[] args) {  
    while(true){  
    System.out.println("infinitive 

while loop");  
    }  
  }  
}  

Output:

infinitive while loop
infinitive while loop
infinitive while loop
infinitive while loop
infinitive while loop
ctrl+c

Now, you need to press ctrl+c to exit from the program.

The do-while Loop

The do-while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.

Syntax

do {

  // code block to be executed

}

while (condition);

The example below uses a do/while loop. The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:

Example

int i = 0;
do {

  System.out.println(i);

  i++;

}

while (i < 5);

 

Do not forget to increase the variable used in the condition, otherwise the loop will never end!