Java With Us

The <code>for</code> Loop in Java

Updated on 2026-04-21 Reviewed by the Java With Us editorial team

The classic for loop runs a block a controlled number of times, tracking an index explicitly. Use it when you need the index — for a range (0 to n-1), to iterate an array in parallel with another, or to step by something other than 1.

Syntax

for (int i = 0; i < 10; i++) {
    System.out.println(i);
}

Three parts separated by ;:

  1. Init — runs once before the loop.
  2. Condition — checked before each iteration; loop ends when false.
  3. Update — runs after each iteration.

Variations

// Count down
for (int i = 10; i > 0; i--) { ... }

// Step by 2
for (int i = 0; i < 100; i += 2) { ... }

// Two variables
for (int i = 0, j = n - 1; i < j; i++, j--) { swap(a, i, j); }

// Infinite
for (;;) {
    if (done) break;
    ...
}

Prefer for-each when you don't need the index

// Index-based
for (int i = 0; i < list.size(); i++) send(list.get(i));

// Enhanced — cleaner
for (User u : list) send(u);

Streams — often clearer

IntStream.range(0, 10).forEach(i -> ... );
IntStream.rangeClosed(1, 100).sum();

Common mistakes

  • Off-by-one — i <= list.size() overshoots by one. Use <.
  • Using .length() on arrays — it's .length (no parens).
  • Modifying the collection inside — triggers ConcurrentModificationException. Use an Iterator or removeIf.
  • Loop variable scoped too widely — declare i inside the for, not before it.

Related

Pillar: Java control flow. See also for-each, ArrayIndexOutOfBoundsException.

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