org.openbp.common.util
Class WeakArrayList

java.lang.Object
  java.util.AbstractCollection<E>
      java.util.AbstractList
          org.openbp.common.util.WeakArrayList

All Implemented Interfaces:

java.lang.Iterable, java.util.Collection, java.util.List

public class WeakArrayList
extends java.util.AbstractList

A weak list works pretty identical to the java.util.ArrayList class except that it usually refers its elements using a weak reference. Weak references enable the garbage collector to remove objects though they are still referenced through the weak ref. In this case, the reference returns null (i. e. through the get(int) method).
Note that the list does not change its size though the references may be garbage-collected. However, if you invoke the trim() method, 'dead' references are removed. Though the implementation of the java.util.List methods always add the elements as weak references, it is also possible to insert elements as hard references using the addHardReference(Object) method, allowing to mix weak and hard references in a single list. This is e. g. used by the ListenerSupport class, which stores the listeners as weak references, but the listener classes as regular references in order to minimize object allocation. Note the the Iterator returned by the AbstractList.iterator() method always returns elements that are validly referenced by the list. The references in the list can be copied to a list that contains regular (hard) references using the createHardList() method.

Author:

Heiko Erhardt

Field Summary

Fields inherited from class java.util.AbstractList

modCount

Constructor Summary

WeakArrayList()
Default constructor.

WeakArrayList(int initialCapacity)
Default constructor.

Method Summary

void	add(int index, java.lang.Object element) Inserts the object at the given position in the list as a weak reference.
void	addHardReference(int index, java.lang.Object element) Inserts the object at the given position in the list as a regular (hard) reference.
void	addHardReference(java.lang.Object element) Adds the object at the end of the list as a regular (hard) reference.
java.util.List	createHardList() Creates a list of hard references to the objects.
java.lang.Object	get(int index) Gets the element at the given index.
java.lang.Object	remove(int index) Removes the object at the given index.
java.lang.Object	set(int index, java.lang.Object element) Sets the object at the given index as a weak reference.
int	size() Gets the size of the list.
void	trim() Trims the list by removing 'dead' references, i\. e\. collected elements.

Methods inherited from class java.util.AbstractList

add, addAll, clear, equals, hashCode, indexOf, iterator, lastIndexOf, listIterator, listIterator, removeRange, subList

Methods inherited from class java.util.AbstractCollection

addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray, toString

Methods inherited from class java.lang.Object

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

Methods inherited from interface java.util.List

addAll, contains, containsAll, isEmpty, remove, removeAll, retainAll, toArray, toArray

Constructor Detail

WeakArrayList

public WeakArrayList()

Default constructor.

WeakArrayList

public WeakArrayList(int initialCapacity)

Default constructor.

Parameters:

initialCapacity - Initial capacity of the list

Method Detail

get

public java.lang.Object get(int index)

Gets the element at the given index.

Specified by:

get in interface java.util.List

Specified by:

get in class java.util.AbstractList

Parameters:

index - Index into the list

Returns:

The element at the given position or null if the element has been garbage-collected.

size

public int size()

Gets the size of the list.

Specified by:

size in interface java.util.Collection

Specified by:

size in interface java.util.List

Specified by:

size in class java.util.AbstractCollection

Returns:

The size includes already collected objects

set

public java.lang.Object set(int index,
                            java.lang.Object element)

Sets the object at the given index as a weak reference.

Specified by:

set in interface java.util.List

Overrides:

set in class java.util.AbstractList

Parameters:

index - List index

element - Element to set

Returns:

The previous object at the given index or null if the object was already collected

add

public void add(int index,
                java.lang.Object element)

Inserts the object at the given position in the list as a weak reference. Automatically creates a weak reference to the object.

Specified by:

add in interface java.util.List

Overrides:

add in class java.util.AbstractList

Parameters:

index - List index

element - Element to add

remove

public java.lang.Object remove(int index)

Removes the object at the given index.

Specified by:

remove in interface java.util.List

Overrides:

remove in class java.util.AbstractList

Parameters:

index - The index of the element to be removed

Returns:

The removed element or null if it was already collected

addHardReference

public void addHardReference(java.lang.Object element)

Adds the object at the end of the list as a regular (hard) reference.

Parameters:

element - Element to add

addHardReference

public void addHardReference(int index,
                             java.lang.Object element)

Inserts the object at the given position in the list as a regular (hard) reference.

Parameters:

index - List index

element - Element to add

createHardList

public java.util.List createHardList()

Creates a list of hard references to the objects.

Returns:

A new list containing only the valid references of this list

trim

public void trim()

Trims the list by removing 'dead' references, i\. e\. collected elements.