Java boolean |= operator

Question

Recently I saw a code using this:

boolean val = something();
val |= somethingElse();

Interesting part is |= (binary like) operator made on boolean primitive type.

It surprised me that |= exist for boolean, as if it was integer type, and searched Java specification for this operator, but could not find any.

I'd be curious if right operand is evaluated if left value already is true.

Can someone point me to Java specification of this?

It is merely val = val | somethingElse(); // somethingElse() expected to return boolean. It is a standard OR — Sudhanshu Umalkar, Mar 14 '13 at 13:54
@SudhanshuUmalkar OP knows that, he asks for specification in a document. — Juvanis, Mar 14 '13 at 13:54
answer is here dudes: http://stackoverflow.com/q/2486472/544983 — Juvanis, Mar 14 '13 at 13:56
I thought there is only || for boolean expressions, so I would expect operator like ||= . Does it make sense to make binary | on boolean? — Pointer Null, Mar 14 '13 at 13:56
No shortcut evaluation, though not mentioned explicitly. Only at || the shortcut logic is mentioned explicitly. — Joop Eggen, Mar 14 '13 at 13:57
@Sudhanshu it's not a standard OR, it's a bitwise OR operator (as opposed to a boolean operator). It is also an aggressive operator, as opposed a short-circuit operator (such as the boolean operator). — xagyg, Mar 14 '13 at 14:00

score 36 · Accepted Answer · edited Jun 20 '20 at 09:12

From the JLS:

15.26.2. Compound Assignment Operators

A compound assignment expression of the form E1 op= E2 is equivalent to E1 = (T) ((E1) op (E2)), where T is the type of E1, except that E1 is evaluated only once.

15.22.2. Boolean Logical Operators &, ^, and |

When both operands of a &, ^, or | operator are of type boolean or Boolean, then the type of the bitwise operator expression is boolean. In all cases, the operands are subject to unboxing conversion (§5.1.8) as necessary.

For |, the result value is false if both operand values are false; otherwise, the result is true.

This means that

val |= somethingElse();

is strictly equivalent to

val = val | somethingElse();

(assuming somethingElse() returns boolean or Boolean).

I'd be curious if right operand is evaluated if left value already is true.

Yes, it would be evaluated, since | does not short-circuit:

15.7.2. Evaluate Operands before Operation

The Java programming language guarantees that every operand of an operator (except the conditional operators &&, ||, and ? :) appears to be fully evaluated before any part of the operation itself is performed.

15.24. Conditional-Or Operator ||

Thus, || computes the same result as | on boolean or Boolean operands. It differs only in that the right-hand operand expression is evaluated conditionally rather than always.

`val |= somethingElse();` has no equivalent in Kotlin. I wonder why... — TheBigBadBoy, Dec 18 '20 at 11:36

Theodore Norvell · Answer 2 · 2019-06-15T20:07:17.163

4

See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.22.2 for the definition of |. See http://docs.oracle.com/javase/specs/jls/se7/html/jls-15.html#jls-15.26.2 for the defintion of |=. The definitions are just what you would think.

What surprises me is the lack of a ||= operator.

edited Jun 15 '19 at 20:07

answered Mar 14 '13 at 13:57

Theodore Norvell

15,366
6
31
45

Jean Waghetti · Answer 3 · 2013-03-14T14:02:03.070

The bitwise logic operators will have the same effect of "normal" logic operators on booleans.

From Java Language Specification 15.22:

When both operands of a &, ^, or | operator are of type boolean or Boolean, then the type of the bitwise operator expression is boolean. In all cases, the operands are subject to unboxing conversion (§5.1.8) as necessary.

For &, the result value is true if both operand values are true; otherwise, the result is false.

For ^, the result value is true if the operand values are different; otherwise, the result is false.

For |, the result value is false if both operand values are false; otherwise, the result is true.

The only real difference is that bitwise operators cant be used to short-circuit evaluation.

For example, this code will throw NullPointerException:

Boolean b1 = new Boolean(true);
Boolean b2 = null;
if (b1 || b2) {
    //no null pointer here;
}
if (b1 | b2) {
    //null pointer here;
}

score 2 · Answer 4 · answered Mar 14 '13 at 14:01

>>I'd be curious if right operand is evaluated if left value already is true.

Bitwise operators (like |, &, ..) evaluate both sides, before completion.

Logical operators (like &&, ||, ..) can skip the evaluation of the second part in some cases. This is called short-circuit.

score -1 · Answer 5 · answered Mar 14 '13 at 16:47

-1

It is not binary it's an "OR" logic statement means

 val |= {something else}

is same as the Boolean expression:

val == val or {something else}

which is inclusive or ( the regular or used in mathematics expressions and computer science)

In some programming languages or is noted by two || signs and in some by one | one of them is SQL and all database languages that I know of DTD JSON etc..

answered Mar 14 '13 at 16:47

sivi

10,654
2
52
51

`|` is not the conditional OR (`||`), it's the bitwise OR. So `val |= something` is the same as `val = val | something`. – foxesque Jan 30 '22 at 23:42

Java boolean |= operator

5 Answers5