2008-04-18 by Roedy Green ©1996-2008 Canadian Mind Productsx = a | b & c;means:
x = ( a | b ) & c;or
x = a | ( b & c );Operators near the top of the table are done first. The lower the precedence number, the eariler the operations are done. Equal precedence operations usually are evaluated left to right, except for ones with right association, which are evaluated right to left. Another way of putting this is right-associated operators like ? have the deepest implied nesting on the right. What a hodge podge!
| Operator Precedence | |||
|---|---|---|---|
| Precedence | Operator | Association | Notes |
| 1 | (prefix) ++
(prefix) -- (unary) + - ~ ! (cast) |
Right (prefix) | ++ prefix means preincrement ~ is bitwise not for ints. Preincrement increments before sampling the value to use in evaluating the rest of the expression. ! is logical not for booleans. Nearly always, you have to put the expression after ! in parentheses. You might as well make a habit of always doing it. |
| 1 | (postfix) ++ --
|
Right (postfix) | ++ postfix means postincrement. Postincrement
increments immediately after sampling the value to use in evaluating the rest of
the expression. Be very careful about using a pre or post incremented variable
elsewhere in an expression. You may be in for a surprise. for example
// Be very careful reusing a pre or post increment variable in an expression. int x = 2; int y = x++ * ++x; // result is y = 8; // it works as if you had coded: int x = 2; int a = x++; // a=2; x=3; int b = ++x; // b=4; x=4 int y = a * b; // y = 8 |
| 2 | * / % | Left (infix) | % is the remainder operator, informally and incorrectly called the modulus operator. / is integer division for ints and floating point division for doubles. |
| 3 | + - | Left (infix) | a - b - c means (a - b) - c not a - ( b - c ), additive operations are performed left to right. + also means concatenation. |
| 4 | << >> >>> | Left (infix) | There is no <<< operator because it would be identical to <<. You have to keep your wits about you when doing unsigned shifts to remember all right shifts must be done with >>>. In JDK 1.5+ the following methods are built-in letting you avoid much low-level bit fiddling: highestOneBit, lowestOneBit, numberOfLeadingZeros, numberOfTrailingZeros, bitCount, rotateLeft, rotateRight, reverse, signum and reverseBytes. |
| 5 | < > <=
>=
instanceof |
Left (infix) | |
| 6 | == != | Left (infix) | == is for comparison. != means not equal.= is for assignment. Pascal’s <> not equal will not work. == and != work on booleans too, often saving a forest of if/elses. |
| 7 | & | Left (infix) | Bitwise AND mostly for for ints. |
| 8 | ^ | Left (infix) | XOR for ints. It is the difference operator. It is true if the boolean
operands are different. e.g.
false ^ false == false false ^ true == true true ^ false == true true ^ true == false It is useful in cryptography because of this magic property of encryption and decryption with a random scrambler number.
long encrypted = message ^ scrambler; long decryped = encrypted ^ scrambler; If you XOR twice with the scrambler, you get right back where you started. For booleans it is clearer to use a != b instead of a ^ b and a == b instead of !( a ^ b) |
| 9 | | | Left (infix) | bitwise OR mostly for ints.
int e = ( a & b << 2 ) | ( c & ( d >>> 1 ) ); // if you trust precedence can be written more tersely: int e = a & b << 2 | c & d >>> 1; |
| 10 | && | Left (infix) | short circuit logical AND for booleans. |
| 11 | || | Left (infix) | short circuit logical OR for booleans. So when you say:
if ( ( ( lowest <= a ) && ( a <= biggest ) ) || notNeeded )all those parentheses are nugatory (computer jargon for not necessary but won’t hurt). You could just as easily have written it, trusting precedence, as: if ( lowest <= a && a <= biggest || notNeeded ) |
| 12 | ? : | Right (ternary) | |
| 13 | = *= /= += -=
<<= >>= >>>= &= ^= |= |
Right (infix) | a += b means a = a + b; a *= b means a = a * b; etc. These make proofreading easier by eliminating typing a variable name twice. |
 |
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