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?

Answer 1

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.