The Java while loop is a control flow statement that controls the execution of the programs repeatedly on the basis of given boolean condition.
Syntax:
while (condition) {
// code to be executed
}
The condition can be any boolean expression. The body of the loop will be executed as long
as the conditional expression is
true
. When condition becomes false, control passes to the
next line of code immediately following the loop. The curly braces are unnecessary if only a
single statement is being repeated.
Flowchart:
Example:
// demonstrate the while loop
public class WhileLoopDemo {
public static void main(String[] args) {
int i = 10;
while (i >= 0) {
System.out.println("i= " + i);
i--; // decrease value of i by 1
}
}
}
Output:
i= 10 i= 9 i= 8 i= 7 i= 6 i= 5 i= 4 i= 3 i= 2 i= 1 i= 0
Java infinite while loop
If you pass true or boolean expression that will be always true after evaluation in the
while loop,
it will be infinite loop.
Syntax:
while (true) {
// code to be executed
}
Example:
// demonstrate the infinite while loop
public class InfiniteWhileLoop {
public static void main(String[] args) {
int i = 0, j = 0;
while (i == j) { // value of i and j will be always same
System.out.println("Infinite while loop..");
// post increment operator
i++;
j++;
}
}
}
Output:
Infinite while loop.. Infinite while loop.. Infinite while loop.. Infinite while loop.. Infinite while loop.. ctrl+c
Now, you need to press ctrl+c to exit from the program.
Empty body of while loop
The body of the while (or any other of Java’s loops) can be empty. This is because a null statement (one that consists only of a semicolon) is syntactically valid in Java. For example, consider the following program:
/*Loop can have empty body.
* Demonstrate the while loop with empty body*/
class NoBody {
public static void main(String args[]) {
int i, j;
i = 100;
j = 200;
// find midpoint between i and j
while (++i < --j) ; // no body in this loop
System.out.println("Midpoint is " + i);
}
}
Output:
Midpoint is 150
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