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Two extraction methods for Java map collection

Java map collection of two ways out, there is a friend in need of reference.


Two extraction methods for map collection:

1, Set, keySet: store all keys in the map into the Set collection because set has the iterator.


, so you can iterate to take all the keys, and then, according to the get method, get the value of each key,.


The removal principle of Map collection: turn the map collection into a set collection, and then take the.
out of the iterator


2, Set>, entrySet: the mapping in the map collection is stored in the set collection,

, and the data type of this relationship is: Map.Entry



Entry is actually a static internal interface Map in.

Why should be defined internally,
?
because only the Map collection has a key value pair will have the key value mapping.

The relationship belongs to an internal thing in the Map collection,.

, and the element in the direct access to the Map collection,.


import java.util.*;
Class MapDemo2
{
Public, static, void, main (String[], args)
{
Map, map = new, HashMap ();
Map.put ("02", "zhangsan2");
Map.put ("03", "zhangsan3");
Map.put ("01", "zhangsan1");
Map.put ("04", "zhangsan4");
Remove / / Map mapping in the collection. In the Set collection.
Set>, entrySet = map.entrySet ();
Iterator>, it = entrySet.iterator ();
While (it.hasNext ())
{
Map.Entry, me = it.next ();
String key = me.getKey ();
String value = me.getValue ();
System.out.println (key+: "+value");
}
*
Get map / / the first set of all key Set collection, keySet ();
Set keySet = map.keySet ();
Have / / Set set. It can obtain the iterator.
Iterator it = keySet.iterator ();
While (it.hasNext ())
{
String key = it.next ();
The get / / map set by the method of key can get the corresponding value.
String value = map.get (key);
System.out.println ("key:", "+key+", "value:", "+value");
}
* /
}
}
*
Map.Entry in fact, Entry is also an interface, which is an internal interface in the Map interface
Interface Map
{
Public static interface Entry
{
Public, abstract, Object, getKey ();
Public, abstract, Object, getValue ();
}
}
Class HashMap implements Map
{
Class Hahs implements Map.Entry
{
Public Object (getKey) {}
Public Object (getValue) {}
}
}
*/


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