java.util
Class AbstractSet

java.lang.Object
  java.util.AbstractCollection
      java.util.AbstractSet

All Implemented Interfaces:

Collection, Set

Direct Known Subclasses:

HashSet

public abstract class AbstractSet
extends AbstractCollection
implements Set

An abstract implementation of Set to make it easier to create your own implementations. In order to create a Set, subclass AbstractSet and implement the same methods that are required for AbstractCollection (although these methods must of course meet the requirements that Set puts on them - specifically, no element may be in the set more than once). This class simply provides implementations of equals() and hashCode() to fulfil the requirements placed on them by the Set interface.

Since:

1.2

See Also:

Collection, AbstractCollection, Set, HashSet, TreeSet, LinkedHashSet

Constructor Summary

protected

AbstractSet() The main constructor, for use by subclasses.

Method Summary

boolean	equals(Object o) Tests whether the given object is equal to this Set.
int	hashCode() Returns a hash code for this Set.
boolean	removeAll(Collection c) Removes from this set all elements in the given collection (optional operation).

Methods inherited from class java.util.AbstractCollection

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, size, toArray, toArray, toString

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface java.util.Set

add, addAll, clear, contains, containsAll, isEmpty, iterator, remove, retainAll, size, toArray, toArray

Constructor Detail

AbstractSet

protected AbstractSet()

The main constructor, for use by subclasses.

Method Detail

equals

public boolean equals(Object o)

Tests whether the given object is equal to this Set. This implementation first checks whether this set is the given object, and returns true if so. Otherwise, if o is a Set and is the same size as this one, it returns the result of calling containsAll on the given Set. Otherwise, it returns false.

Specified by:

equals in interface Collection

Specified by:

equals in interface Set

Overrides:

equals in class Object

Parameters:

o - the Object to be tested for equality with this Set

Returns:

true if the given object is equal to this Set

See Also:

Object.hashCode()

hashCode

public int hashCode()

Returns a hash code for this Set. The hash code of a Set is the sum of the hash codes of all its elements, except that the hash code of null is defined to be zero. This implementation obtains an Iterator over the Set, and sums the results.

Specified by:

hashCode in interface Collection

Specified by:

hashCode in interface Set

Overrides:

hashCode in class Object

Returns:

a hash code for this Set

See Also:

Object.equals(Object), System.identityHashCode(Object)

removeAll

public boolean removeAll(Collection c)

Removes from this set all elements in the given collection (optional operation). This implementation uses size() to determine the smaller collection. Then, if this set is smaller, it iterates over the set, calling Iterator.remove if the collection contains the element. If this set is larger, it iterates over the collection, calling Set.remove for all elements in the collection. Note that this operation will fail if a remove methods is not supported.

Specified by:

removeAll in interface Collection

Specified by:

removeAll in interface Set

Overrides:

removeAll in class AbstractCollection

Parameters:

c - the collection of elements to remove

Returns:

true if the set was modified as a result

Throws:

UnsupportedOperationException - if remove is not supported

NullPointerException - if the collection is null

See Also:

AbstractCollection.remove(Object), Collection.contains(Object), Iterator.remove()