AbstractMapK,V

AbstractMap<K,V>

java.util

---

Java 1.2

collection

This abstract class is a partial implementation of the Map interface that makes it easy to define simple custom Map implementations . To define an unmodifiable map, subclass AbstractMap and override the entrySet( ) method so that it returns a set of Map.Entry objects. (Note that you must also implement Map.Entry , of course.) The returned set should not support add( ) or remove( ) , and its iterator should not support remove( ) . In order to define a modifiable Map , you must additionally override the put( ) method and provide support for the remove( ) method of the iterator returned by enTRySet( ).iterator( ) . In addition, it is conventional that all Map implementations define two constructors: one that accepts no arguments and another that accepts a Map of initial mappings.

AbstractMap defines all Map methods in terms of its entrySet( ) and put( ) methods and the remove( ) method of the entry set iterator. Note, however, that the implementation is based on a linear search of the Set returned by enTRySet( ) and is not efficient when the Map contains more than a handful of entries. Some subclasses may want to override additional AbstractMap methods to improve performance. HashMap and treeMap use different algorithms are are substantially more efficient.

Figure 16-3. java.util.AbstractMap<K,V>

 public abstract class  AbstractMap<K,V>  implements Map<K,V> {  // Protected Constructors  protected  AbstractMap  ( );  // Methods Implementing Map  public void  clear  ( );        public boolean  containsKey  (Object  key  );        public boolean  containsValue  (Object  value  );        public abstract Set<Map.Entry<K,V>>  entrySet  ( );        public boolean  equals  (Object  o  );        public V  get  (Object  key  );        public int  hashCode  ( );        public boolean  isEmpty  ( );        public Set<K>  keySet  ( );        public V  put  (K  key  , V  value  );        public void  putAll  (Map<? extends K,? extends V>  t  );        public V  remove  (Object  key  );        public int  size  ( );        public Collection<V>  values  ( );  // Public Methods Overriding Object  public String  toString  ( );  // Protected Methods Overriding Object   1.4  protected Object  clone  ( ) throws CloneNotSupportedException;   } 

Subclasses

EnumMap , HashMap , IdentityHashMap , TReeMap , WeakHashMap , java.util.concurrent.ConcurrentHashMap