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map interface methods

Posted on 2016-08-05
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Last Modified: 2016-08-07
Hi,
I wonder why Map interface has equals() and hashCode() methods again in Entry  method as they are already there before?

[i]boolean
equals(Object
paramObject);
int
hashCode();[/i]
public
static
abstract
interface
[b]Entry[/b]<K,
V>
{
K
getKey();
V
getValue();
V
setValue(V
paramV);
boolean
equals(Object
paramObject);
int
hashCode();
}

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please advise
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Question by:gudii9
3 Comments
 
LVL 14

Expert Comment

by:CPColin
ID: 41744325
It's probably so the Javadocs for those methods can clarify that implementations should be looking at both the key and the value.
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LVL 7

Author Comment

by:gudii9
ID: 41745118
It's probably so the Javadocs for those methods can clarify that implementations should be looking at both the key and the value.
if you see below javedocs for map interface that also has equals and hascode() methods as attached.

http://docs.oracle.com/javase/8/docs/api/java/util/Map.html

my question is why below Map.Entry as below has same methods again

http://docs.oracle.com/javase/8/docs/api/java/util/Map.Entry.html
hashCodeMap.png
equalsMap.png
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LVL 28

Accepted Solution

by:
dpearson earned 2000 total points
ID: 41746282
If I understand your question correctly it's because they are two different things.

Map.equals() is for deciding if 2 maps are the same.  That means they contain *all* of the same entries.

Map.Entry.equals() is for deciding if 2 entries in a map are the same.

It's the difference between deciding if two libraries contain all of the same books (Map.equals) or if two books in a library are copies of the same book (Map.Entry.equals).

Doug
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