Java in a Nutshell, 5th Edition

Name

AbstractCollection<E>

Synopsis

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