AbstractCollectionE

AbstractCollection<E>

java.util

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Java 1.2

collection

This abstract class is a partial implementation of Collection that makes it easy to define custom Collection implementations . To create an unmodifiable collection, simply override size ( ) and iterator( ) . The Iterator object returned by iterator( ) has to support only the hasNext( ) and next ( ) methods . To define a modifiable collection, you must additionally override the add( ) method of AbstractCollection and make sure the Iterator returned by iterator( ) supports the remove( ) method. Some subclasses may choose to override other methods to tune performance. In addition, it is conventional that all subclasses provide two constructors: one that takes no arguments and one that accepts a Collection argument that specifies the initial contents of the collection.

Note that if you subclass AbstractCollection directly, you are implementing a bag an unordered collection that allows duplicate elements. If your add( ) method rejects duplicate elements, you should subclass AbstractSet instead. See also AbstractList .

Figure 16-1. java.util.AbstractCollection<E>

 public abstract class  AbstractCollection<E>  implements Collection<E> {  // Protected Constructors  protected  AbstractCollection  ( );  // Methods Implementing Collection  public boolean  add  (E  o  );        public boolean  addAll  (Collection<? extends E>  c  );        public void  clear  ( );        public boolean  contains  (Object  o  );        public boolean  containsAll  (Collection<?>  c  );        public boolean  isEmpty  ( );        public abstract Iterator<E>  iterator  ( );        public boolean  remove  (Object  o  );        public boolean  removeAll  (Collection<?>  c  );        public boolean  retainAll  (Collection<?>  c  );        public abstract int  size  ( );        public Object[ ]  toArray  ( );        public <T> T[ ]  toArray  (T[ ]  a  );  // Public Methods Overriding Object  public String  toString  ( );   } 

Subclasses

AbstractList , AbstractQueue , AbstractSet