Java Tutorial · Control Flow · Lesson 15 of 37

Java Loops

while, do-while, for and for-each loops, with break and continue.

while and do-while

Example 1

public class Main {
    public static void main(String[] args) {
        int n = 1;
        while (n < 50) {
            n *= 2;
        }
        System.out.println(n);
        int tries = 0;
        do {
            tries++;
        } while (tries < 0);
        System.out.println("ran " + tries + " time(s)");
    }
}

Output

64
ran 1 time(s)

Run this on your computer — see “Get Started” for setup.

for

The classic for loop has an initialiser, a condition and an update:

Example 2

public class Main {
    public static void main(String[] args) {
        for (int i = 5; i > 0; i--) {
            System.out.print(i + " ");
        }
        System.out.println("liftoff!");
    }
}

Output

5 4 3 2 1 liftoff!

Run this on your computer — see “Get Started” for setup.

for-each

The enhanced for loop iterates over arrays and collections — use it whenever you don't need the index:

Example 3

public class Main {
    public static void main(String[] args) {
        String[] langs = {"Java", "Kotlin", "Scala"};
        for (String lang : langs) {
            System.out.println(lang + " runs on the JVM");
        }
        int total = 0;
        for (int x : new int[]{3, 5, 7}) total += x;
        System.out.println(total);
    }
}

Output

Java runs on the JVM
Kotlin runs on the JVM
Scala runs on the JVM
15

Run this on your computer — see “Get Started” for setup.

break, continue and labels

break leaves the loop; continue jumps to the next iteration. A label lets you break out of an outer loop:

Example 4

public class Main {
    public static void main(String[] args) {
        for (int i = 1; i <= 10; i++) {
            if (i % 3 == 0) continue;
            if (i > 7) break;
            System.out.print(i + " ");
        }
        System.out.println();
        outer:
        for (int row = 1; row <= 3; row++) {
            for (int col = 1; col <= 3; col++) {
                if (row * col == 4) {
                    System.out.println("found 4 at " + row + "," + col);
                    break outer;
                }
            }
        }
    }
}

Output

1 2 4 5 7 
found 4 at 2,2

Run this on your computer — see “Get Started” for setup.

Test yourself

Which loop is best for visiting every element of a list when you don't need the index?

while
do-while
for-each
switch

Show answer

Answer: for-each