====== Summary of Operator Precedence Rules ======

These notes are extracted from Appendix C.3 of //Groovy Programming// (See [[lecture0#Reading|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:
<code groovy>2 + 3 * 4 + 5</code> 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 |
|  | ''%%^= |= <<= >>= >>>=%%'' | | |




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