Interesting boolean syntax

Question

I've lately bumped in something weird. Consider the following method:

public boolean addAll(Collection<T> col) {
    boolean added = false;

    for(T t : col)
        added |= add(t);

    return added;
}

Although I understand what this wants to do, that's - not change it to false, if it exceeded at least once (if a later element failed). But what does this actually mean. How is it read. And are there any similar gadgets in boolean?

Don't you mean `|=`? I'm not sure your `=|` is valid syntax. — Quetzalcoatl, Apr 04 '13 at 22:41
`added` is true if at least one item was successfully added. — assylias, Apr 04 '13 at 22:42
http://stackoverflow.com/questions/2325349/what-does-the-operator-do-in-java. Next time try SymbolHound: http://symbolhound.com/?q=java+%7C%3D+tutorial — Matt Ball, Apr 04 '13 at 22:45

score 2 · Answer 1 · answered Apr 04 '13 at 22:42

2

The |= operator is equivalent to this:

added = ( added | add(t) );

answered Apr 04 '13 at 22:42

jahroy

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score 2 · Accepted Answer · answered Apr 04 '13 at 22:43

2

It is a bitwise-or combined with an equals.

As such, if it has been set to true (i.e. 1) before, if you bitwise or either a true or false (1 or 0) with it, you'll always return true (1) as 0 OR 1 = 1 and 1 OR 1 = 1.

It is in effect the same as:

added = (added | add(t));

answered Apr 04 '13 at 22:43

Quetzalcoatl

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@MouseEvent: Not sure if that's valid, but even if it is, `||` is lazy-evaluated which means that if the left value is already true, then the `add()` function won't be called – mpen Apr 04 '13 at 22:46
That is a logical OR, which behaves differently to a bitwise OR. See: http://stackoverflow.com/questions/4014535/differences-in-boolean-operators-vs-and-vs – Quetzalcoatl Apr 04 '13 at 22:46
@Mark: Indeed it is lazily evaluated, the logical OR will short circuit whereas the bitwise OR will not. – Quetzalcoatl Apr 04 '13 at 22:48
@MouseEvent `||=` is not a valid operator. – assylias Apr 04 '13 at 22:49
I knew about bitwise operators, but never knew that booleans works this way too... – Mordechai Apr 04 '13 at 22:58
In Java, there is no special relationship between `true` and `1` – Steve Kuo Apr 04 '13 at 23:49
I was merely utilizing the effective similarity between `1` and `0` and `true` and `false`, since we're talking bitwise here I felt it would help with the explanation. – Quetzalcoatl Apr 05 '13 at 08:55

Interesting boolean syntax

2 Answers2