org.scopemvc.util
Class WeakSet

java.lang.Object
  |
  +--org.scopemvc.util.WeakSet

All Implemented Interfaces:

java.util.Collection, java.util.Set

public class WeakSet

extends java.lang.Object

implements java.util.Set

Holds a set of objects where the fact that the object is contained within the set does not prevent it from being garbage collected. Sort of like WeakHashMap only no values. Could have used WeakHashMap and just set the value to null I guess???

Version:

$Revision: 1.6 $

Author:

Simon Harris

Constructor Summary

WeakSet()
Default constructor.

Method Summary

boolean	add(java.lang.Object o) Ensures that this collection contains the specified element (optional operation).
boolean	addAll(java.util.Collection c) Adds all of the elements in the specified collection to this collection (optional operation).
void	clear() Removes all of the elements from this collection (optional operation).
boolean	contains(java.lang.Object o) Returns true if this collection contains the specified element.
boolean	containsAll(java.util.Collection c) Returns true if this collection contains all of the elements in the specified collection.
boolean	equals(java.lang.Object o) Compares the specified object with this collection for equality.
int	hashCode() Returns the hash code value for this collection.
boolean	isEmpty() Returns true if this collection contains no elements.
java.util.Iterator	iterator() Returns an iterator over the elements in this collection.
boolean	remove(java.lang.Object o) Removes a single instance of the specified element from this collection, if it is present (optional operation).
boolean	removeAll(java.util.Collection c) Removes all this collection's elements that are also contained in the specified collection (optional operation).
boolean	retainAll(java.util.Collection c) Retains only the elements in this collection that are contained in the specified collection (optional operation).
int	size() Returns the number of elements in this collection.
java.lang.Object[]	toArray() Returns an array containing all of the elements in this collection.
java.lang.Object[]	toArray(java.lang.Object[] a) Returns an array containing all of the elements in this collection whose runtime type is that of the specified array.

Methods inherited from class java.lang.Object

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

Constructor Detail

WeakSet

public WeakSet()

Default constructor.

Method Detail

isEmpty

public boolean isEmpty()

Returns true if this collection contains no elements.

Specified by:

isEmpty in interface java.util.Set

Returns:

true if this collection contains no elements

retainAll

public boolean retainAll(java.util.Collection c)

Retains only the elements in this collection that are contained in the specified collection (optional operation). In other words, removes from this collection all of its elements that are not contained in the specified collection.

Specified by:

retainAll in interface java.util.Set

Parameters:

c - elements to be retained in this collection.

Returns:

true if this collection changed as a result of the call

Throws:

java.lang.UnsupportedOperationException - if the retainAll method is not supported by this Collection.

See Also:

remove(Object), contains(Object)

contains

public boolean contains(java.lang.Object o)

Returns true if this collection contains the specified element. More formally, returns true if and only if this collection contains at least one element e such that (o==null ? e==null : o.equals(e)) .

Specified by:

contains in interface java.util.Set

Parameters:

o - element whose presence in this collection is to be tested.

Returns:

true if this collection contains the specified element

toArray

public java.lang.Object[] toArray(java.lang.Object[] a)

Returns an array containing all of the elements in this collection whose runtime type is that of the specified array. If the collection fits in the specified array, it is returned therein. Otherwise, a new array is allocated with the runtime type of the specified array and the size of this collection.

If this collection fits in the specified array with room to spare (i.e., the array has more elements than this collection), the element in the array immediately following the end of the collection is set to null . This is useful in determining the length of this collection only if the caller knows that this collection does not contain any null elements.)

If this collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

Like the toArray method, this method acts as bridge between array-based and collection-based APIs. Further, this method allows precise control over the runtime type of the output array, and may, under certain circumstances, be used to save allocation costs

Suppose l is a List known to contain only strings. The following code can be used to dump the list into a newly allocated array of String :

    String[] x = (String[]) v.toArray(new String[0]);
 

Note that toArray(new Object[0]) is identical in function to toArray() .

Specified by:

toArray in interface java.util.Set

Parameters:

a - the array into which the elements of this collection are to be stored, if it is big enough; otherwise, a new array of the same runtime type is allocated for this purpose.

Returns:

an array containing the elements of this collection

Throws:

java.lang.ArrayStoreException - the runtime type of the specified array is not a supertype of the runtime type of every element in this collection.

removeAll

public boolean removeAll(java.util.Collection c)

Removes all this collection's elements that are also contained in the specified collection (optional operation). After this call returns, this collection will contain no elements in common with the specified collection.

Specified by:

removeAll in interface java.util.Set

Parameters:

c - elements to be removed from this collection.

Returns:

true if this collection changed as a result of the call

Throws:

java.lang.UnsupportedOperationException - if the removeAll method is not supported by this collection.

See Also:

remove(Object), contains(Object)

toArray

public java.lang.Object[] toArray()

Returns an array containing all of the elements in this collection. If the collection makes any guarantees as to what order its elements are returned by its iterator, this method must return the elements in the same order.

The returned array will be "safe" in that no references to it are maintained by this collection. (In other words, this method must allocate a new array even if this collection is backed by an array). The caller is thus free to modify the returned array.

This method acts as bridge between array-based and collection-based APIs.

Specified by:

toArray in interface java.util.Set

Returns:

an array containing all of the elements in this collection

iterator

public java.util.Iterator iterator()

Returns an iterator over the elements in this collection. There are no guarantees concerning the order in which the elements are returned (unless this collection is an instance of some class that provides a guarantee).

Specified by:

iterator in interface java.util.Set

Returns:

an Iterator over the elements in this collection

remove

public boolean remove(java.lang.Object o)

Removes a single instance of the specified element from this collection, if it is present (optional operation). More formally, removes an element e such that (o==null ? e==null : o.equals(e)) , if this collection contains one or more such elements. Returns true if this collection contained the specified element (or equivalently, if this collection changed as a result of the call).

Specified by:

remove in interface java.util.Set

Parameters:

o - element to be removed from this collection, if present.

Returns:

true if this collection changed as a result of the call

Throws:

java.lang.UnsupportedOperationException - remove is not supported by this collection.

clear

public void clear()

Removes all of the elements from this collection (optional operation). This collection will be empty after this method returns unless it throws an exception.

Specified by:

clear in interface java.util.Set

Throws:

java.lang.UnsupportedOperationException - if the clear method is not supported by this collection.

hashCode

public int hashCode()

Returns the hash code value for this collection. While the Collection interface adds no stipulations to the general contract for the Object.hashCode method, programmers should take note that any class that overrides the Object.equals method must also override the Object.hashCode method in order to satisfy the general contract for the Object.hashCode method. In particular, c1.equals(c2) implies that c1.hashCode()==c2.hashCode() .

Specified by:

hashCode in interface java.util.Set

Overrides:

hashCode in class java.lang.Object

Returns:

the hash code value for this collection

See Also:

Object.hashCode(), Object.equals(Object)

addAll

public boolean addAll(java.util.Collection c)

Adds all of the elements in the specified collection to this collection (optional operation). The behavior of this operation is undefined if the specified collection is modified while the operation is in progress. (This implies that the behavior of this call is undefined if the specified collection is this collection, and this collection is nonempty.)

Specified by:

addAll in interface java.util.Set

Parameters:

c - elements to be inserted into this collection.

Returns:

true if this collection changed as a result of the call

Throws:

java.lang.UnsupportedOperationException - if this collection does not support the addAll method.

java.lang.ClassCastException - if the class of an element of the specified collection prevents it from being added to this collection.

java.lang.IllegalArgumentException - some aspect of an element of the specified collection prevents it from being added to this collection.

See Also:

add(Object)

size

public int size()

Returns the number of elements in this collection. If this collection contains more than Integer.MAX_VALUE elements, returns Integer.MAX_VALUE .

Specified by:

size in interface java.util.Set

Returns:

the number of elements in this collection

containsAll

public boolean containsAll(java.util.Collection c)

Returns true if this collection contains all of the elements in the specified collection.

Specified by:

containsAll in interface java.util.Set

Parameters:

c - collection to be checked for containment in this collection.

Returns:

true if this collection contains all of the elements in the specified collection

See Also:

contains(Object)

add

public boolean add(java.lang.Object o)

Ensures that this collection contains the specified element (optional operation). Returns true if this collection changed as a result of the call. (Returns false if this collection does not permit duplicates and already contains the specified element.)

Collections that support this operation may place limitations on what elements may be added to this collection. In particular, some collections will refuse to add null elements, and others will impose restrictions on the type of elements that may be added. Collection classes should clearly specify in their documentation any restrictions on what elements may be added.

If a collection refuses to add a particular element for any reason other than that it already contains the element, it must throw an exception (rather than returning false ). This preserves the invariant that a collection always contains the specified element after this call returns.

Specified by:

add in interface java.util.Set

Parameters:

o - element whose presence in this collection is to be ensured.

Returns:

true if this collection changed as a result of the call

Throws:

java.lang.UnsupportedOperationException - add is not supported by this collection.

java.lang.ClassCastException - class of the specified element prevents it from being added to this collection.

java.lang.IllegalArgumentException - some aspect of this element prevents it from being added to this collection.

equals

public boolean equals(java.lang.Object o)

Compares the specified object with this collection for equality.

While the Collection interface adds no stipulations to the general contract for the Object.equals , programmers who implement the Collection interface "directly" (in other words, create a class that is a Collection but is not a Set or a List ) must exercise care if they choose to override the Object.equals . It is not necessary to do so, and the simplest course of action is to rely on Object 's implementation, but the implementer may wish to implement a "value comparison" in place of the default "reference comparison." (The List and Set interfaces mandate such value comparisons.)

The general contract for the Object.equals method states that equals must be symmetric (in other words, a.equals(b) if and only if b.equals(a) ). The contracts for List.equals and Set.equals state that lists are only equal to other lists, and sets to other sets. Thus, a custom equals method for a collection class that implements neither the List nor Set interface must return false when this collection is compared to any list or set. (By the same logic, it is not possible to write a class that correctly implements both the Set and List interfaces.)

Specified by:

equals in interface java.util.Set

Overrides:

equals in class java.lang.Object

Parameters:

o - Object to be compared for equality with this collection.

Returns:

true if the specified object is equal to this collection

See Also:

Object.equals(Object), Set.equals(Object), List.equals(Object)