Package org.eclipse.core.runtime

Class ListenerList<E>

java.lang.Object
org.eclipse.core.runtime.ListenerList<E>
Type Parameters:
E - the type of listeners in this list
All Implemented Interfaces:
Iterable<E>
public class ListenerList<E> extends Object implements Iterable<E>
This class is a thread safe list that is designed for storing lists of listeners. The implementation is optimized for minimal memory footprint, frequent reads and infrequent writes. Modification of the list is synchronized and relatively expensive, while accessing the listeners is very fast. For legacy code, readers are given access to the underlying array data structure for reading, with the trust that they will not modify the underlying array.

A listener list handles the same listener being added multiple times, and tolerates removal of listeners that are the same as other listeners in the list. For this purpose, listeners can be compared with each other using either equality or identity, as specified in the list constructor.

Use an enhanced 'for' loop to notify listeners. The recommended code sequence for notifying all registered listeners of say, FooListener#eventHappened(Event), is: 

ListenerList<FooListener> fooListeners = new ListenerList<>();
//...
for (FooListener listener : fooListeners) {
        listener.eventHappened(event);
}

Legacy code may still call getListeners() and then use a 'for' loop to iterate the Object[]. This might be insignificantly faster, but it lacks type-safety and risks inadvertent modifications to the array.

This class can be used without OSGi running.

Since:
org.eclipse.equinox.common 3.2

  • Field Summary

    Fields
    Modifier and Type
    Field
    Description
    static final int
    EQUALITY
    Mode constant (value 0) indicating that listeners should be considered the same if they are equal.
    static final int
    IDENTITY
    Mode constant (value 1) indicating that listeners should be considered the same if they are identical.

  • Constructor Summary

    Constructors
    Constructor
    Description
    ListenerList()
    Creates a listener list in which listeners are compared using equality.
    ListenerList(int mode)
    Creates a listener list using the provided comparison mode.

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    add(E listener)
    Adds a listener to this list.
    void
    clear()
    Removes all listeners from this list.
    Object[]
    getListeners()
    Returns an array containing all the registered listeners.
    boolean
    isEmpty()
    Returns whether this listener list is empty.
    Iterator<E>
    iterator()
    Returns an iterator over all the registered listeners.
    Stream<E>
    parallelStream()
    Returns a parallel Stream over the registered listeners.
    void
    remove(Object listener)
    Removes a listener from this list.
    int
    size()
    Returns the number of registered listeners.
    Spliterator<E>
    spliterator()
    Returns a Spliterator covering the registered listeners.
    Stream<E>
    stream()
    Returns a sequential Stream over the registered listeners.
    String
    toString()
     

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

    Methods inherited from interface java.lang.Iterable

    forEach

  • Field Details

    • EQUALITY

      public static final int EQUALITY
      Mode constant (value 0) indicating that listeners should be considered the same if they are equal.
      See Also:

    • IDENTITY

      public static final int IDENTITY
      Mode constant (value 1) indicating that listeners should be considered the same if they are identical.
      See Also:

  • Constructor Details

    • ListenerList

      public ListenerList()
      Creates a listener list in which listeners are compared using equality.

    • ListenerList

      public ListenerList(int mode)
      Creates a listener list using the provided comparison mode.
      Parameters:
      mode - The mode used to determine if listeners are the same.

  • Method Details

    • add

      public void add(E listener)
      Adds a listener to this list. This method has no effect if the same listener is already registered.
      Parameters:
      listener - the non-null listener to add

    • getListeners

      public Object[] getListeners()
      Returns an array containing all the registered listeners. The resulting array is unaffected by subsequent adds or removes. If there are no listeners registered, the result is an empty array. Use this method when notifying listeners, so that any modifications to the listener list during the notification will have no effect on the notification itself.

      Note: Callers of this method must not modify the returned array.

      Note: The recommended and type-safe way to iterate this list is to use an enhanced 'for' statement, see ListenerList. This method is deprecated for new code.

      Returns:
      the list of registered listeners

    • iterator

      public Iterator<E> iterator()
      Returns an iterator over all the registered listeners. The resulting iterator is unaffected by subsequent adds or removes. Use this method when notifying listeners, so that any modifications to the listener list during the notification will have no effect on the notification itself.
      Specified by:
      iterator in interface Iterable<E>
      Returns:
      an iterator
      Since:
      org.eclipse.equinox.common 3.8

    • isEmpty

      public boolean isEmpty()
      Returns whether this listener list is empty.
      Returns:
      true if there are no registered listeners, and false otherwise

    • remove

      public void remove(Object listener)
      Removes a listener from this list. Has no effect if the same listener was not already registered.
      Parameters:
      listener - the non-null listener to remove

    • size

      public int size()
      Returns the number of registered listeners.
      Returns:
      the number of registered listeners

    • clear

      public void clear()
      Removes all listeners from this list.

    • spliterator

      public Spliterator<E> spliterator()
      Returns a Spliterator covering the registered listeners.

      The spliterator reports Spliterator.SIZED, Spliterator.SUBSIZED, Spliterator.ORDERED, and Spliterator.IMMUTABLE

      Specified by:
      spliterator in interface Iterable<E>
      Returns:
      a spliterator for listeners
      Since:
      org.eclipse.equinox.common 3.9

    • stream

      public Stream<E> stream()
      Returns a sequential Stream over the registered listeners.
      Returns:
      a sequential Stream over the registered listeners.
      Since:
      org.eclipse.equinox.common 3.9

    • parallelStream

      public Stream<E> parallelStream()
      Returns a parallel Stream over the registered listeners.
      Returns:
      a parallel Stream over the registered listeners.
      Since:
      org.eclipse.equinox.common 3.9

    • toString

      public String toString()
      Overrides:
      toString in class Object