Java While Loop

What is a while loop?

Think of a while loop as a question that Java keeps asking before every pass: "Is this condition still true?" If the answer is yes, it runs the code inside the braces once more, then asks again. The moment the answer becomes no, the loop stops and your program continues with whatever comes after it.

int i = 0;

while (i < 5) {
  System.out.println("i is now " + i);
  i++;
}

// Output:
// i is now 0
// i is now 1
// i is now 2
// i is now 3
// i is now 4

Notice the three parts working together: we start with i set to 0, the condition i < 5 decides whether to keep going, and i++ moves us one step closer to stopping. If you forget that last step, i would stay 0 forever and the loop would never end.

A practical example

While loops shine when you do not know in advance how many times you will repeat. Here we keep doubling a number until it passes a target, without knowing the exact count of steps beforehand.

int value = 1;
int steps = 0;

while (value < 100) {
  value = value * 2;
  steps++;
}

System.out.println("Reached " + value + " in " + steps + " doublings");
// Output: Reached 128 in 7 doublings

The three things every while loop needs

• Initialization: set up a starting value before the loop begins.
• Condition: a boolean test checked before each pass; the loop runs only while it is true.
• Update: change something inside the loop so the condition will eventually become false.