Re: Need clarification on Object.equals.

From:

Lars Enderin <lars.enderin@telia.com>

Newsgroups:

comp.lang.java.programmer

Date:

Wed, 19 Dec 2012 17:43:46 +0100

Message-ID:

<50D1EEC2.6090607@telia.com>

2012-12-19 17:22, Arne Vajh?j skrev:

On 12/19/2012 11:13 AM, FredK wrote:

On Tuesday, December 18, 2012 10:56:19 AM UTC-8, Peter Duniho wrote:

On Tue, 18 Dec 2012 04:48:16 -0800, Roedy Green wrote:

Node a = new Gate();
Monitor b = new Monitor();
System.out.println(a.equals(b)); // --> prints 'true'

Gate or one of its superclasses is implementing equals.

And doing it incorrectly, I'd say.

Why would you think it was done incorrectly?
For most classes, a.equals(b) is not the same as a==b.
Think about string:
string a = "abc");
string b = new string(a);
Clearly a==b is false, but a.equals(b) is true.

Usually the equals() method returns true if the internal state of both
objects is the same.

It is rather unusual to have objects of different classes considered
equals.

Your example is different.

Both Gate and Monitor were extensions of AbstractSet, and empty, which
eventually led to Set#containsAll, and thus equals, returning true.

--
Lars Enderin