Java Loops

Repeat work without copy-pasting code.

for loop

The most common loop. Three parts: initialization, condition, increment.

for loop

for (int i = 0; i < 5; i++) {
    System.out.println("Count: " + i);
}
// Count: 0  Count: 1  Count: 2  Count: 3  Count: 4

while loop

Repeats while a condition is true. Check happens before each iteration.

while loop

int n = 10;
while (n > 0) {
    System.out.println(n);
    n--;
}
System.out.println("Liftoff!");

do-while loop

Like while, but the body executes at least once — the check is at the bottom.

do-while

int n = 0;
do {
    System.out.println("Runs once even if false");
    n++;
} while (n < 0);   // false from the start, but body still ran once

for-each loop (enhanced for)

Cleanest way to iterate over arrays and collections — no index management:

for-each

String[] names = {"Raman", "Aman", "Priya"};

for (String name : names) {
    System.out.println(name);
}

Read it as: "for each String called name in names".

Which loop should I use?

Need the index? Use for.
Iterating a collection or array? Use for-each.
Loop count unknown, depends on a condition? Use while.
Need to run at least once? do-while (rare).

break — exit a loop early

break

for (int i = 0; i < 10; i++) {
    if (i == 5) break;
    System.out.println(i);
}
// 0 1 2 3 4

continue — skip to next iteration

continue

for (int i = 0; i < 5; i++) {
    if (i % 2 == 0) continue;  // skip even numbers
    System.out.println(i);
}
// 1 3

Nested loops

Multiplication table

for (int i = 1; i <= 3; i++) {
    for (int j = 1; j <= 3; j++) {
        System.out.print(i * j + " ");
    }
    System.out.println();
}
// 1 2 3
// 2 4 6
// 3 6 9

Beware infinite loops while (true) with no break runs forever. for (int i=0; i<n; i--) never terminates because i goes the wrong way. Always make sure your condition can become false.

← If / Else Arrays →