for
Java
for (int i = 1; i <= 5; i++) {
System.out.println(i);
}while
Java
int i = 1;
while (i <= 5) {
System.out.println(i);
i++;
}do...while
Runs the body at least once:
Java
int i = 10;
do {
System.out.println(i); // prints 10
i++;
} while (i <= 5);Enhanced for (for-each)
The one to reach for when iterating a collection or array:
Java
int[] marks = {88, 74, 91};
for (int m : marks) {
System.out.println(m);
}
List<String> names = List.of("Sita", "Ram", "Hari");
for (String n : names) {
System.out.println(n);
}You cannot modify the array/list structure through a for-each — use an
indexed for or an Iterator for that.
break and continue
Java
for (int i = 1; i <= 10; i++) {
if (i % 2 == 0) continue; // skip evens
if (i > 7) break; // stop entirely
System.out.println(i); // 1 3 5 7
}Labelled break
For escaping nested loops in one step:
Java
outer:
for (int i = 0; i < 3; i++) {
for (int j = 0; j < 3; j++) {
if (i * j > 2) break outer;
System.out.println(i + "," + j);
}
}Use sparingly — often a well-named method with an early return reads
better.
Common mistakes
Java
// Off-by-one: <= on an array length goes out of bounds
for (int i = 0; i <= arr.length; i++) { } // ArrayIndexOutOfBoundsException
for (int i = 0; i < arr.length; i++) { } // correct
// Infinite loop: forgetting to advance the counter
int i = 0;
while (i < 5) {
System.out.println(i); // i never changes
}