Loops in Java

Loops repeat code while a condition or iteration rule allows it. Java provides for, enhanced for, while, and do-while loops.

The for loop#

Use a for loop when the iteration setup and update are naturally expressed together.

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

The loop initializes i to 1, checks i <= 5, executes the body, then increments i. It stops when the condition becomes false.

The while loop#

A while loop checks its condition before each iteration.

int count = 3;
while (count > 0) {
    System.out.println(count);
    count--;
}

Make sure that something in the loop can eventually make the condition false. Otherwise, the loop may never terminate.

The do-while loop#

A do-while loop runs its body at least once because its condition is checked at the end.

int attempt = 0;
do {
    attempt++;
} while (attempt < 1);

Enhanced for loop#

Use the enhanced for loop to visit each element in an array or collection:

String[] languages = {"Java", "Python", "JavaScript"};
for (String language : languages) {
    System.out.println(language);
}

break and continue#

break exits the nearest loop. continue skips the rest of the current iteration and moves to the next one. Use them when they make the logic clearer, not as a replacement for a well-structured condition.

Practice#

Print the numbers from 1 to 20. Then print only even numbers in that range. Finally, calculate the sum of the numbers from 1 to 100.