Java Operators

Operators are the symbols that do something with values: add them, compare them, combine conditions. You have already used + and =. This topic shows the operators you will use every day, grouped by what they do.

Arithmetic operators

public class Main {
    public static void main(String[] args) {
        int a = 17, b = 5;
        System.out.println(a + b);
        System.out.println(a - b);
        System.out.println(a * b);
        System.out.println(a / b);
        System.out.println(a % b);
        System.out.println(17.0 / 5);
    }
}

22
12
85
3
2
3.4

Division of two int values drops the remainder, as you saw in Type Casting. The % operator gives that remainder; it is handy to test whether a number is even (n % 2 == 0).

Increment, decrement and compound assignment

x++ adds 1 to x, and x-- subtracts 1. The compound assignment operators change a variable using its own value: x += 5 means x = x + 5, and the same works for -=, *=, /= and %=.

public class Main {
    public static void main(String[] args) {
        int count = 10;
        count++;
        System.out.println(count);
        count -= 4;
        System.out.println(count);
        count *= 3;
        System.out.println(count);
    }
}

11
7
21

Comparison operators

Comparisons give a boolean result: true or false. They are the building blocks of decisions in the If ... Else topic.

Do not confuse = (store a value) with == (compare two values). For text, use equals instead of ==; the Strings topic explains why.

Logical operators

&& (and) is true when both sides are true, || (or) when at least one side is true, and ! (not) turns true into false and false into true:

public class Main {
    public static void main(String[] args) {
        int age = 20;
        boolean hasTicket = true;
        System.out.println(age >= 18 && hasTicket);
        System.out.println(age < 12 || age > 65);
        System.out.println(!hasTicket);
    }
}

true
false
false

Java stops evaluating && as soon as the left side is false, and || as soon as the left side is true. This is called short-circuit evaluation.

Order of operations

As in mathematics, *, / and % are done before + and -. Use brackets to make the order clear or to change it:

public class Main {
    public static void main(String[] args) {
        System.out.println(2 + 3 * 4);
        System.out.println((2 + 3) * 4);
        System.out.println(0.1 + 0.2);
    }
}

14
20
0.30000000000000004

The last line shows a surprise: decimal numbers are stored in binary, so 0.1 + 0.2 is not exactly 0.3. For money, programs often count in whole paise or cents with int or long.

Practice exercises

1. Print the remainder when 100 is divided by 7.
2. Start with int x = 3; and use compound operators to make it 3, then 9, then 4, printing each step.
3. Print whether the year 2024 is divisible by 4 and not divisible by 100, using %, && and !=.