What is the reason for the interface The card has an internal Entry interface?
I am talking about how developed Java classes and interfaces just saw java/util/Map.java
and I still have doubts? please help me by answering.
What is the reason for the interface to Map
have an internal interface Entry
?
Have a look at the source code java / util / Map.java and answer.
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Map<K,V>
can be thought of as associative storage (i.e. a container that connects keys with their values). It can also be thought of as a set of pairs, where the first element is the key and the second element is its corresponding value.
Most of the methods in it Map<K,V>
support the associative view of the map container. Map.Entry<K,V>
the interface supports a different kind of map - i.e. as a set of key-value pairs.
Each card provides access to what is called a set of records, which is a set of pairs from a card. Each pair is represented by a copy Map.Entry<K,V>
.
Map<Integer,String> myMap = ...
for (Map.Entry<Integer,String> e : myMap.entrySet()) {
System.out.println(e.getKey()+" ---> "+e.getValue());
}
It was possible to define the interface MapEntry<K,V>
outside Map<K,V>
. However, since the interface is very closely related to the map, the decision to embed the interface inside the map makes sense.
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