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The difference between two Java statements:! = Vs! Equals

This code:

elem1!=elem2

equivalent to this?

 !elem1.equals(elem2)

It compiles in both directions, but I'm still not sure about that ...

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2 answers

== (and by extension != ) check the identity of the object, that is, if both objects belong to the same instance. equals tests the concept of a higher level identity, usually whether the “values” of objects are equal. This means that anyone who implemented equals on this particular object. Therefore, they are not the same thing.

A common example where these two are not the same are strings in which two different instances can have the same content (the same character string), in which case the comparison == false, but equals returns true.

The default implementation of equals (on Object ) uses == internally, so the results will be the same for objects that do not override equals (excluding zeros, of course)

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In general, they are not the same. The first version checks whether elem1 and elem2 references to the same object (provided that they are not primitive types). The second version calls a method specific to a particular type to check whether two (possibly different) projects are "equal" in a sense (often this is just a check that all their member fields are identical).

I don't think this has anything to do with generics per se.

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