Java Operators

What are operators?

An operator performs an action on one or more values, which we call operands. In the expression 5 + 3, the plus sign is the operator and 5 and 3 are the operands. Java offers several categories of operators, each suited to a different kind of job.

• Arithmetic operators do maths: + - * / and %.
• Assignment operators store or update values: = += -= and friends.
• Comparison operators test how two values relate: == != > < >= and <=.
• Logical operators combine boolean conditions: && || and !.

A quick taste of each family

The example below touches every category at once so you can see how they fit together in a normal program. Read it top to bottom and notice how the result of one operation feeds into the next.

public class Main {
  public static void main(String[] args) {
    int a = 10, b = 3;

    int sum = a + b;            // arithmetic -> 13
    boolean bigger = a > b;     // comparison -> true
    boolean both = bigger && (sum > 5); // logical -> true
    sum += 100;                 // assignment -> sum is now 113

    System.out.println(sum);    // 113
    System.out.println(both);   // true
  }
}

Operator categories at a glance

Precedence: who goes first?

Just like in school maths, Java evaluates some operators before others. Multiplication and division happen before addition and subtraction, and you can always use parentheses to make the order explicit. When in doubt, add brackets; they cost nothing and make your intent obvious.

public class Main {
  public static void main(String[] args) {
    int result1 = 2 + 3 * 4;   // 14, because * runs before +
    int result2 = (2 + 3) * 4; // 20, brackets force + first

    System.out.println(result1);
    System.out.println(result2);
  }
}

The following pages break each family down in detail, with tables and runnable examples. Master these four groups and you can express almost any calculation or decision your programs need to make.