Java For Loop

A for loop is a loop that gathers its start, its condition, and its change in one header. The header sits in parentheses after the for keyword.

Count by twos

The change part adds 2 on each pass. The counter prints the even numbers from 0 to 6.

public class Main {
  public static void main(String[] args) {
    for (int i = 0; i <= 6; i += 2) {
      System.out.println(i);
    }
  }
}

Count down

The counter starts at 3. The change part subtracts 1 on each pass.

public class Main {
  public static void main(String[] args) {
    for (int i = 3; i > 0; i--) {
      System.out.println(i);
    }
  }
}

Nested loops print a grid

The outer loop makes one row on each pass. The inner loop prints three stars for that row.

public class Main {
  public static void main(String[] args) {
    for (int row = 0; row < 3; row++) {
      for (int col = 0; col < 3; col++) {
        System.out.print("*");
      }
      System.out.println();
    }
  }
}

Example

public class Main {
  public static void main(String[] args) {
    for (int i = 1; i <= 5; i++) {
      System.out.println("7 x " + i + " = " + (7 * i));
    }
  }
}

Key points

The header holds three parts separated by semicolons.
The first part sets the starting value.
The second part is the condition, checked before each pass.
The third part changes the counter after each pass.
A loop inside another loop is a nested loop.

In this example, i runs from 1 to 5. Each pass builds one line of the 7 times table. The product part multiplies 7 by the current value of i. The five lines print the products in order.

Note

A for loop fits well when the number of passes is known in advance.

Try it Yourself

Edit the code, then press Run.

Running is simulated

public class Main {
  public static void main(String[] args) {
    for (int i = 1; i <= 5; i++) {
      System.out.println("7 x " + i + " = " + (7 * i));
    }
  }
}

Exercise

Which part of a for header is checked before each pass?

The starting value The condition The change The block