Java Notes-10
来源：程序员人生 发布时间：2015-05-08 07:48:40 阅读次数：3319次
Summay: The Map Interface, Collection implementations
-Maps store and retrieve elements with key values
e.g:
Map<String, Date> dateMap = new HashMap<String, Date>();
dateMap.put( "today", new Date() );
Date today = dateMap.get( "today" );
-Functions:
public V put( K key , V value )//This method adds the specified key/value pair to the map.
public V get( K key )//This method retrieves the value corresponding to key from the map.
public V remove( K key )//This method removes the value corresponding to key from the map
public int size()//Use this method to find the number of key/value pairs in this map
public Set keySet()//This method returns a Set that contains all the keys in this map.
public Collection values()//Use this method to retrieve all the values in this map
-Map has one child interface, SortedMap . A SortedMap maintains its key/value pairs sorted
in a particular order according to the key values.
-All of the methods of the Collection interface would appear to make sense for Map ,
except for iterator() . A Map , again, has two sets of objects: keys and values, and separate
iterators for each. This is why a Map does not implement Collection
-ConcurrentMap, It extends the base Map interface and adds atomic put, remove, and replace functionality that is
useful for concurrent programming
public V putIfAbsent( K key, V value )//This method associates the value with the key only if the key was not already in use.
public boolean remove( Object key, Object value )//This method removes the mapping (key and value) only if the current value asso
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