equals operator and a graph node

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Monty Hall - 06 Nov 2005 07:43 GMT

Hello,

Suppose I have an object that's a vertex in a graph. Supppose I have a
vector that contains this vertex. Suppose I use the vector's
contain(Object) method. Does java first compare by memory reference ? Or
does it do a "deep" equals?

Monty.

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Thomas Hawtin - 06 Nov 2005 08:46 GMT

> Suppose I have an object that's a vertex in a graph. Supppose I have a
> vector that contains this vertex. Suppose I use the vector's
> contain(Object) method. Does java first compare by memory reference ? Or
> does it do a "deep" equals?

What does the documentation say?

http://download.java.net/jdk6/docs/api/java/util/Collection.html#contains(java.l
ang.Object)

Tom Hawtin

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Chris Uppal - 06 Nov 2005 09:37 GMT

> Suppose I use the vector's
> contain(Object) method. Does java first compare by memory reference ? Or
> does it do a "deep" equals?

It uses the object's equals() method which by default is the same as comparing
by ==, but may be overridden to do a more meaningful comparison. So the answer
is that it depends on the objects in question.

Incidentally, this is specified in the JavaDoc for java.util.Vector.contains(),
though I admit it doesn't exactly jump out at you when you read it.

-- chris

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equals operator and a graph node

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