[SOLVED] Reason for the existence of non-short-circuit logical operators

Reason for the existence of non-short-circuit logical operators

When used with boolean operands, & and | become logical operators per Section 15.22.2 of the JLS. Unlike && and ||, however, these don't short-circuit; they always evaluate both sides. I have a silly question: Why are the less-efficient non-short-circuit logical operators (&, |) still there, when we have the more-efficient short-circuit logical operators (&&, ||)? I mean, what is the real usage of the non-short-circuit logical operators, as opposed to with the short-circuit logical operators? In other words, what is the usage of always evaluating both sides by using the non-short-circuit logical operators?

Solution

Consider the case where you want any side-effects to always occur, regardless of whether the left-hand expression evaluates true or false. E.g., contrast:

if (foo() & bar()) {
    // Only call this if both operations returned true
}

with

if (foo() && bar()) {
    // Only call this if both operations returned true
}

Let's assume both foo and bar have effects that we want to have happen regardless of whether foo returns true or false. In the first one above, I know that bar will always get called and have its effect. In the latter, of course, bar may or may not get called. If we didn't have the non-short-circuit version, we'd have to use temporary variables:

boolean fooResult = foo();
boolean barResult = bar();
if (fooResult && barResult) {
    // ...
}

You might argue (I probably would) that you should do that anyway, because it's way too easy to misread if (foo() & bar()), but there we go, a pragmatic reason for having non-short-circuit versions.