Operators

Operators perform calculations and comparisons: adding numbers, checking whether one value is greater than another, combining conditions. This lesson covers arithmetic, assignment, increment, comparison, logical and ternary operators, and the precedence rules that decide which runs first.

Arithmetic

void main() {
    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);
}

22
12
85
3
2

% (modulus) gives the remainder after division — useful for checking even numbers (n % 2 == 0) or wrapping around. Integer division by zero throws an ArithmeticException; with doubles it gives Infinity or NaN instead.

Compound assignment

void main() {
    int total = 10;
    total += 5;
    total -= 3;
    total *= 2;
    total /= 4;
    total %= 4;
    System.out.println(total);
}

2

x += 5 is short for x = x + 5. (It also casts back to the variable's type automatically, so byteVar += 1 compiles where byteVar = byteVar + 1 doesn't.)

Increment and decrement

void main() {
    int count = 5;
    count++;
    System.out.println(count);

    int a = 5;
    int b = a++;
    System.out.println(a + " " + b);

    int c = 5;
    int d = ++c;
    System.out.println(c + " " + d);
}

6
6 5
6 6

Both a++ and ++a add one. The difference is the value of the expression: a++ evaluates to the old value, ++a to the new one. On a line by itself, there's no difference; inside larger expressions it's easy to misread, so avoid mixing them in.

Comparison

void main() {
    int x = 7;
    System.out.println(x == 7);
    System.out.println(x != 7);
    System.out.println(x > 3);
    System.out.println(x <= 6);
}

true
false
true
false

Comparisons produce a boolean. Note == (compare) vs = (assign). For objects such as strings, == checks whether two references point to the same object — use .equals() to compare contents (lesson 9).

Logical operators

void main() {
    int age = 25;
    boolean hasId = true;
    System.out.println(age >= 18 && hasId);
    System.out.println(age < 12 || age > 65);
    System.out.println(!hasId);
}

true
false
false

&& (and), || (or) and ! (not). && and || short-circuit: if the left side already decides the result, the right side isn't evaluated. That makes checks like name != null && name.isEmpty() safe.

The ternary operator

void main() {
    int stock = 0;
    String label = stock > 0 ? "In stock" : "Sold out";
    System.out.println(label);
}

Sold out

condition ? valueIfTrue : valueIfFalse picks one of two values. It's great for simple choices; use if for anything longer.

Precedence

void main() {
    System.out.println(2 + 3 * 4);
    System.out.println((2 + 3) * 4);
    System.out.println(10 - 4 - 3);
    System.out.println(true || false && false);
}

14
20
3
true

Operators with equal priority mostly run left to right. When in doubt, add parentheses — they cost nothing and help readers.

Bitwise operators

void main() {
    int flags = 0b0101;
    System.out.println(flags & 0b0100);
    System.out.println(flags | 0b0010);
    System.out.println(flags ^ 0b0001);
    System.out.println(1 << 4);
}

4
7
4
16

&, |, ^ (xor), ~, and the shifts <<, >>, >>> work on individual bits. You'll mostly meet them in low-level code, flags and hashing.

Try it yourself

Convert a number of seconds into hours, minutes and seconds.

2h 3m 5s