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map interface methods
Posted on 2016-08-05
Hi,
I wonder why Map interface has equals() and hashCode() methods again in Entry method as they are already there before?
please advise
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();
}
please advise
[X]
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3 Comments
It's probably so the Javadocs for those methods can clarify that implementations should be looking at both the key and the value.
Active 1 day ago
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
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
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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