Java With Us

Arithmetic Operators in Java

Updated on 2026-04-21 Reviewed by the Java With Us editorial team

Java has seven arithmetic operators: +, -, *, /, %, ++, --. They operate on numeric types (byte, short, int, long, float, double, char). + is also the string-concatenation operator when either operand is a String.

Basics

int a = 10, b = 3;
a + b;        // 13
a - b;        // 7
a * b;        // 30
a / b;        // 3      — integer division truncates
a % b;        // 1      — remainder

Integer vs floating division

7 / 2;          // 3     — both operands int
7 / 2.0;        // 3.5   — at least one double → double result
(double) 7 / 2; // 3.5   — explicit cast
7 % 2;          // 1
7.5 % 2;        // 1.5   — remainder works on floats too

Increment and decrement

int i = 5;
int a = i++;      // post-increment: a = 5, i = 6
int b = ++i;      // pre-increment:  b = 7, i = 7
int c = i--;      // post-decrement
int d = --i;      // pre-decrement

In isolation they behave the same (i++ alone just increments). In an expression, the pre/post distinction matters.

Overflow

int m = Integer.MAX_VALUE;
m + 1;                              // wraps to Integer.MIN_VALUE — no exception
Math.addExact(m, 1);                // ✅ throws ArithmeticException

String concatenation

"result: " + 1 + 2;    // "result: 12"  — left-to-right, string wins
1 + 2 + " = sum";       // "3 = sum"     — ints first, then joined
"a" + null;             // "anull"       — null is stringified
"a" + (char) 65;        // "aA"          — char is widened to String via Character

Always parenthesise the non-string part when mixing: "result: " + (a + b).

Compound assignment

x += 5;    // x = x + 5
x -= 3;    // x = x - 3
x *= 2;
x /= 4;
x %= 3;

Compound operators include an implicit cast: byte b = 1; b += 0.5; compiles (cast to byte), while b = b + 0.5; does not.

Common mistakes

  • Integer division surprise — 5 / 2 is 2, not 2.5.
  • Silent overflow in large products — multiply as long from the start.
  • i += 1 vs ++i — equivalent for primitives, but ++i on an AtomicInteger doesn't exist; use incrementAndGet().
  • String concatenation order — "a" + 1 + 2 is "a12", not "a3".

Related

Pillar: Java operators. See also int, double.

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