Java Language For Loops

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Example

for (int i = 0; i < 100; i++) {
    System.out.println(i);
}

The three components of the for loop (separated by ;) are variable declaration/initialization (here int i = 0), the condition (here i < 100), and the increment statement (here i++). The variable declaration is done once as if placed just inside the { on the first run. Then the condition is checked, if it is true the body of the loop will execute, if it is false the loop will stop. Assuming the loop continues, the body will execute and finally when the } is reached the increment statement will execute just before the condition is checked again.

The curly braces are optional (you can one line with a semicolon) if the loop contains just one statement. But, it's always recommended to use braces to avoid misunderstandings and bugs.

The for loop components are optional. If your business logic contains one of these parts, you can omit the corresponding component from your for loop.

int i = obj.getLastestValue(); // i value is fetched from a method
    
for (; i < 100; i++) { // here initialization is not done
    System.out.println(i);
}

The for (;;) { function-body } structure is equal to a while (true) loop.

Nested For Loops

Any looping statement having another loop statement inside called nested loop. The same way for looping having more inner loop is called 'nested for loop'.

    for(;;){
        //Outer Loop Statements
        for(;;){
            //Inner Loop Statements
        }
        //Outer Loop Statements
    }

Nested for loop can be demonstrated to print triangle shaped numbers.

for(int i=9;i>0;i--){//Outer Loop
    System.out.println();
    for(int k=i;k>0;k--){//Inner Loop -1
        System.out.print(" ");
    }
    for(int j=i;j<=9;j++){//Inner Loop -2
        System.out.print(" "+j);
    }
 }
If / Else