Explain While Loop In Java With Program And Example, How to write While Loop In Java
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while
The
while
loop is Java’s most fundamental loop statement. It repeats a statement or block
while its controlling expression is true. Here is its general form:
while( condition ) {
// body of loop
}
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.
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The Java Language
Here is a
while
loop that counts down from 10, printing exactly ten lines of “tick”:
// Demonstrate the while loop.
class While {
public static void main(String args[]) {
int n = 10;
while(n > 0) {
System.out.println("tick " + n);
n--;
}
}
}
When you run this program, it will “tick” ten times:
tick 10
tick 9
tick 8
tick 7
tick 6
tick 5
tick 4
tick 3
tick 2
tick 1
Since the
while
loop evaluates its conditional expression at the top of the loop, the body
of the loop will not execute even once if the condition is false to begin with. For example, in
the following fragment, the call to
println( )
is never executed:
int a = 10, b = 20;
while(a > b)
System.out.println("This will not be displayed");
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:
// The target of a loop can be empty.
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
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Control Statements
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Part I:
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System.out.println("Midpoint is " + i);
}
}
This program finds the midpoint between
i
and . It generates the following output:
j
Midpoint is 150
Here is how this
while
loop works. The value of
i
is incremented, and the value of
j
is
decremented. These values are then compared with one another. If the new value of
i
is still
less than the new value of , then the loop repeats. If
j
i
is equal to or greater than , the loop
j
stops. Upon exit from the loop,
i
will hold a value that is midway between the original values
of
i
and . (Of course, this procedure only works when
j
i
is less than
j
to begin with.) As you
can see, there is no need for a loop body; all of the action occurs within the conditional
expression, itself. In professionally written Java code, short loops are frequently coded
without bodies when the controlling expression can handle all of the details itself.