Boolean.TRUE == myBoolean vs. Boolean.TRUE.equals(myBoolean)

Question

Is there ever a situation where using equals(Boolean) and == would return different results when dealing with Boolean objects?

Boolean.TRUE == myBoolean;

Boolean.TRUE.equals(myBoolean);

I'm not thinking about primitive types here, just Boolean objects.

Here's why I asked the question: `Boolean a1 = true; Boolean a2 = true; System.out.println(a1 == a2);`. The output is "true" — Edd, May 08 '13 at 16:10

score 11 · Accepted Answer · edited May 23 '17 at 12:09

11

How about:

System.out.println(new Boolean(true) == new Boolean(true));
System.out.println(new Boolean(true) == Boolean.TRUE);

(both print false, for the same reason as any other type of objects).

edited May 23 '17 at 12:09

Community

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answered May 08 '13 at 09:36

assylias

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why it print false? can you explain? – muneebShabbir May 08 '13 at 09:41
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`new Boolean(true) == Boolean.TRUE` would showcase the issue even better. – Marko Topolnik May 08 '13 at 09:42
its false because we are comparing objects with `==` sign? – muneebShabbir May 08 '13 at 09:43
@muneebShabbir The reason why it prints false is the same a for any other object: http://stackoverflow.com/questions/2772763/why-equals-method-when-we-have-operator – assylias May 08 '13 at 09:56
Thanks for this... I wasn't sure if there are only ever 2 Boolean objects and all references point to those objects but I guess not – Edd May 08 '13 at 11:24

Marko Topolnik · Answer 2 · 2013-05-08T09:53:18.877

3

It would be dangerous to use == because myBoolean may not have originated from one of the constants, but have been constructed as new Boolean(boolValue), in which case == would always result in false. You can use just

myBoolean.booleanValue()

with neither == nor equals involved, giving reliable results. If you must cater for null-values as well, then there's nothing better than your equals approach.

edited May 08 '13 at 09:53

answered May 08 '13 at 09:36

Marko Topolnik

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Though that would lead back to the primitive value. – Menno May 08 '13 at 09:39
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@Aquillo You make it sound like that's a problem. Why would it be a problem? Note that the result of either of OP's expressions is the same primitive boolean. – Marko Topolnik May 08 '13 at 09:40
To me it would be a possible solution instead of a problem. Though OP stated his question is not to discuss the processing of primitives. – Menno May 08 '13 at 09:41
@MarkoTopolnik primitive values are a problem with tri-state booleans (true/false/null) – John Dvorak May 08 '13 at 09:42
@Aquillo OP is only indicating that `myBoolean` is an object. – Marko Topolnik May 08 '13 at 09:44
@MarkoTopolnik yeah... what's the shortest way to safely compare tri-state booleans? – John Dvorak May 08 '13 at 09:44
@JanDvorak No, you're right: `TRUE.equals(myBoolean)` is the shortest way---though not to *compare* tri-state booleans, but to determine if *one* such value is `true`. – Marko Topolnik May 08 '13 at 09:45
@MarkoTopolnik only if the left hand side is a constant or two-state boolean – John Dvorak May 08 '13 at 09:46
@JanDvorak ...you mean, as in `TRUE.equals(myBoolean)`? :) – Marko Topolnik May 08 '13 at 09:47
@MarkoTopolnik yeah, that would work. But, what if you had two tristates you wanted to check for equality? – John Dvorak May 08 '13 at 09:48
@JanDvorak Then you are in for a couple more characters of code :) `left == null? right == null : left.equals(right)` – Marko Topolnik May 08 '13 at 09:51
In ruby, neither of `TrueClass`, `FalseClass` or `NilClass` have a public constructor. – John Dvorak May 08 '13 at 09:55

score 2 · Answer 3 · edited May 23 '19 at 12:41

2

if (Boolean.TRUE == new Boolean(true)) {
    System.out.println("==");
}

if (Boolean.TRUE.equals(myBoolean)) {
    System.out.println("equals");
}

In this case first one is false. Only second if condition is true.

It Prints:

equals

edited May 23 '19 at 12:41

Clijsters

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answered May 08 '13 at 09:39

Vineet Singla

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score 0 · Answer 4 · answered May 08 '13 at 09:39

0

== only works for primitive types
when you compare Objects you should always use o.equls(Object ob)

answered May 08 '13 at 09:39

Kuchi

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Except enums. You can use == for Enum objects because Java guaranteed it is singletone – Ali Katkar Dec 26 '21 at 17:48

Boolean.TRUE == myBoolean vs. Boolean.TRUE.equals(myBoolean)

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