for & for-each

Loops repeat work without repeating code. Java has three loop forms; the counting for comes first:

for (int i = 1; i <= 5; i++) {
    System.out.println("tick " + i);
}

Read the header as three sentences: start with i at 1; keep going while i <= 5; after every pass, step i forward. The variable i exists only inside the loop — declare it there, not outside.

The counting pattern that covers most real loops:

int[] scores = {72, 85, 90};
for (int i = 0; i < scores.length; i++) {
    System.out.println(scores[i]);
}

Zero-based counting with i < length (not <=) is the Java convention — arrays and Strings index from 0, so i from 0 to length-1 touches every element exactly once. Off-by-one bugs (<=) throw ArrayIndexOutOfBoundsException at the last step.

The enhanced for ("for-each") visits every element without an index at all:

for (int s : scores) {
    System.out.println(s);
}

Use for-each whenever you need the elements; use the classic for when you need the position or a custom step (i += 3). Both loops here print the same three numbers — choosing the loop is choosing which idea (index vs element) your code is about.

Next: loops that run until something happens.