Operators in Java

Why this matters

Every calculation, every condition and every loop you write depends on operators.

Example

public class Operators {
    public static void main(String[] args) {
        int a = 17, b = 5;

        System.out.println("Sum: " + (a + b));
        System.out.println("Division: " + (a / b));      // integer division
        System.out.println("Remainder: " + (a % b));
        System.out.println("a > b ? " + (a > b));
        System.out.println("Both true? " + (a > b && b > 0));

        a += 3;   // same as a = a + 3
        System.out.println("a after += 3: " + a);
    }
}

Step by step

1. 1`a / b` with two ints gives 3, not 3.4 — the decimal part is thrown away.
2. 2`a % b` gives the remainder, 2. This is very useful for even/odd checks.
3. 3`a > b` produces a boolean, true or false.
4. 4`&&` is logical AND: true only when both sides are true.
5. 5`a += 3` is shorthand for `a = a + 3`.

Key points

• int / int gives an int — cast to double for decimals
• % gives remainder, perfect for even/odd and digit problems
• == compares values for primitives; use .equals() for Strings
• && and || short-circuit: the right side may not be evaluated

Common mistakes

• Using = (assignment) where == (comparison) is needed
• Expecting 17/5 to be 3.4 without casting
• Comparing Strings with == instead of .equals()

Try it yourself

• Check whether a number is even using %.
• Find the average of three int marks correctly as a decimal.