Summary of Operator Precedence Rules
These notes are extracted from Appendix C.3 of Groovy Programming (See Recommended Reading).
An expression involving operators of equal precedence is resolved by the associativity of the operators. This defines the direction in which the operators possessing the same precedence are executed. For example, the expression:
2 + 3 * 4 + 5
is evaluated in the following manner. Multiplication has the highest precedence so is evaluate first. The expression is reduced to 2 + 12 + 5 with the two addition operators having equal precedence. The associativity of additive operators is left to right, and so the 2 and 12 are first added to give 14, then 14 and 5 are added to produce 19 as the final result.
If, in the expression 2 + 3 * 4 + 5 the programmer intended to perform the additions before performing the multiplication, he or she should use parenthesis around the sub expressions. The expression would be presented as (2 + 3) * (4 + 5), which evaluates to 5 * 9 or 45.
The full table of operator precedence and associativity for Groovy (and hence Java) is given in Table 1.
Table 1 Operator Precedence and Associativity
| Category | Operators | Example | Associativity |
|---|---|---|---|
| Array subscript | [ ] | a[2] | Left to right |
| Member access | . | a.b() | |
| Post-fix unary operators | expr++ expr-- | x++ | Right to left |
| (Pre-fix) unary operators | ++expr --expr + - = ! | -x | Right to left |
| Multiplicative | * / % | x * y | Left to right |
| Additive | + - | x + y | Left to right |
| Shift | << >> >>> | x « y | Left to right |
| Relational | < <= >= instanceof | x <= y | Left to right |
| Equality | == != <=> | x != y | Left to right |
| Bitwise And | & | x & y | Left to right |
| Bitwise exclusive Or | ^ | x ^ y | Left to right |
| Bitwise inclusive Or | | | x | y | Left to right |
| Logical And | && | x && y | Left to right |
| Logical Or | || | x || y | Left to right |
| Conditional | :? | a < b ? x : y | Left to right |
| Assignment | = += -= *= /= %= &= | x += y | Right to left |
^= |= <<= >>= >>>= |