Comparing Character, Integer and similar types in Java: Use equals or ==?

java equals primitive
Uri picture Uri · Apr 9, 2009 · Viewed 33.6k times · Source

I wanted to make sure about something in Java: If I have a Character or an Integer or a Long and those sort of things, should I use equals or is == sufficient?

I know that with strings there are no guarantees that there is only one instance of each unique string, but I'm not sure about other boxed types.

My intuition is to use equals, but I want to make sure I'm not wasting performance.

Answer

Jon Skeet picture Jon Skeet · Apr 9, 2009

EDIT: The spec makes some guarantees for boxing conversions. From section 5.1.7:

If the value p being boxed is true, false, a byte, a char in the range \u0000 to \u007f, or an int or short number between -128 and 127, then let r1 and r2 be the results of any two boxing conversions of p. It is always the case that r1 == r2.

The implementation can use a larger pool, mind you.

I would really avoid writing code which relies on that though. Not because it might fail, but because it's not obvious - few people will know the spec that well. (I previously thought it was implementation-dependent.)

You should use equals or compare the underlying values, i.e.

if (foo.equals(bar))

or

if (foo.intValue() == bar.intValue())

Note that even if the autoboxing were guaranteed to use fixed values, other callers can always create separate instances anyway.

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