What is different between for loop and while loop in java?

Answer 1

Features wise they are both the same. The difference lies in the way they are implemented.

while Loop

The while loop is good for scenarios where you don't know how many times a block or statement should repeat, but you want to continue looping as long as some condition is true. A while statement looks like this:

while (expression) {

// do stuff

}

In this case, as in all loops, the expression (test) must evaluate to a boolean result. The body of the while loop will only execute if the expression (sometimes called the "condition") results in a value of true. Once inside the loop, the loop body will repeat until the condition is no longer met because it evaluates to false.

Any variables used in the expression of a while loop must be declared before the expression is evaluated. In other words, you can't say

while (int x = 2) { } // This is not legal

The key point to remember about a while loop is that it might not run at all. If the test expression is false the first time the while expression is checked, the loop body will be skipped and the program will begin executing at the first statement after the while loop. Look at the following example:

int x = 8;

while (x > 8) {

System.out.println("in the loop");

x = 10;

}

System.out.println("past the loop");

Running this code produces

past the loop

Because the expression (x > 8) evaluates to false, none of the code within the while loop ever executes

The for loop is especially useful for flow control when you already know how many times you need to execute the statements in the loop's block. The for loop declaration has three main parts, besides the body of the loop:

• Declaration and initialization of variables

• The boolean expression (conditional test)

• The iteration expression

The three for declaration parts are separated by semicolons. The following two examples demonstrate the for loop. The first example shows the parts of a for loop in a pseudocode form, and the second shows a typical example of a for loop.

for (/*Initialization*/ ; /*Condition*/ ; /* Iteration */) {

/* loop body */

}

Ex:

for (int i = 0; i<10; i++) { System.out.println("i is " + i); }