Write Java conditions and loops

Separate the condition from the update

A for loop initializes a counter, checks its condition before each iteration, and applies its update after the body. With i < 4, the values 0, 1, 2, and 3 enter the body. Changing < to <= adds an iteration and may cause an array index error.

A total accumulates values, while a count records how many values satisfy a condition. Initialize both before the loop. In the example, only even i values contribute to the total, so the output is 6.

public class Demo {
    public static void main(String[] args) {
        int total = 0;
        for (int i = 1; i <= 4; i++) {
            if (i % 2 == 0) {
                total += i;
            }
        }
        System.out.println(total);
    }
}

Use short-circuit evaluation

In a && b, Java evaluates b only if a is true. In a || b, it evaluates b only if a is false. A guard such as index < values.length && values[index] != 0 checks the bound before accessing the array.

For nested loops, count how many times the inner body runs for each outer value. If each of n rows scans n columns, the body runs n squared times. Doubling n approximately quadruples that work.

Check yourself