When programming, you will encounter blocks of code that are to be repeated over and over again until a specific requirement becomes false. Hence, this block of code will run in a loop.
One specific type of loop is a while loop. This form of a loop continues to run as long as a specific condition returns true. A while loop
follows the syntax given below:
class HelloWorld { public static void main( String args[] ) { while(condition){ //body of loop } } }
Look at the code above from lines 4 to 6 to understand the syntax of a while loop in Java:
while
keyword is followed by round brackets, ()
condition
is writtencondition
is checked each time a loop is run. If the condition returns true
then the loop body executes, otherwise the loop breaks.The illustration below shows the logical route that a while loop follows:
Now that we know what syntax the while loop follows and how to write it, let’s look at a few coding examples.
1. Starting while
with a false condition
The example below shows what happens when you execute a while loop when the condition is false such that the loop does not execute even once:
class HelloWorld { public static void main( String args[] ) { int i=10; while(i<5){ System.out.println("The value of i: "+ i); } } }
2. Executing a while
loop
The example below shows how the loop runs until the conditional statement returns false. For each iteration of the loop, the value of i
is doubled. When the value becomes greater than 30, the loop should terminate.
class HelloWorld { public static void main( String args[] ) { int i=1; while(i<30){ System.out.println("The value of i is "+ i); i=i*2; } } }
3. Using while
to iterate over an array
We can even use while loops to iterate over an array.
First we define an array
and find out its length, len
, using the length
property of arrays.
Then we define an index
variable to iterate over the array
.
The while loop, from lines 6 to 9, is run till index
becomes equal to len
indicating that the entire array is traversed.
In each iteration, the loop condition checks if the index
is less than len
. If the result of the expression is true, i.e. index
is less than len
, then the value of the array at index
is printed and index
is incremented
The example below shows how it can be done:
class HelloWorld { public static void main( String args[] ) { int array [] = {5,4,3,2,1}; int len = array.length; int index = 0; while(index<len){ System.out.println(array[index]); index = index + 1; } } }
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