Package org.apache.bookkeeper.common.util

Class Watchable<T>

  • All Implemented Interfaces:
    Recyclable
    Direct Known Subclasses:
    FileInfo, TransientLedgerInfo
    public class Watchable<T>
extends java.lang.Object
implements Recyclable
    This class represents an watchable object, or "data" in the model-view paradigm. It can be subclassed to represent an object that the application wants to have watched.

    An watchable object can have one or more watchers. An watcher may be any object that implements interface Watcher. After an watchable instance changes, an application calling the Watchable's notifyWatchers method causes all of its watchers to be notified of the change by a call to their update method.

    A watcher is automatically removed from the watchers list once an event is fired to the watcher.

    Note that this notification mechanism has nothing to do with threads and is completely separate from the wait and notify mechanism of class Object.

    When an watchable object is newly created, its set of watchers is empty. If a same watcher is added multiple times to this watchable, it will receive the notifications multiple times.

    • Method Summary

      All Methods Instance Methods Concrete Methods 
      Modifier and Type Method Description
      boolean addWatcher​(Watcher<T> w)
      Adds an watcher to the set of watchers for this object, provided that it is not the same as some watcher already in the set.
      boolean deleteWatcher​(Watcher<T> w)
      Deletes an watcher from the set of watcher of this object.
      void deleteWatchers()
      Clears the watcher list so that this object no longer has any watchers.
      (package private) int getNumWatchers()  
      <R> void notifyWatchers​(java.util.function.Function<R,​T> valueFn, R value)
      Notify the watchers with the update value.
      void recycle()
      Recycle the instance.

      • Methods inherited from class java.lang.Object

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

    • Method Detail

      • getNumWatchers

        int getNumWatchers()

      • addWatcher

        public boolean addWatcher​(Watcher<T> w)
        Adds an watcher to the set of watchers for this object, provided that it is not the same as some watcher already in the set. The order in which notifications will be delivered to multiple watchers is not specified. See the class comment.
        Parameters:
        w - an watcher to be added.
        Returns:
        true if a watcher is added to the list successfully, otherwise false.
        Throws:
        java.lang.NullPointerException - if the parameter o is null.

      • deleteWatcher

        public boolean deleteWatcher​(Watcher<T> w)
        Deletes an watcher from the set of watcher of this object. Passing null to this method will have no effect.
        Parameters:
        w - the watcher to be deleted.

      • notifyWatchers

        public <R> void notifyWatchers​(java.util.function.Function<R,​T> valueFn,
                               R value)
        Notify the watchers with the update value.
        Parameters:
        value - value to notify

      • deleteWatchers

        public void deleteWatchers()
        Clears the watcher list so that this object no longer has any watchers.

      • recycle

        public void recycle()
        Description copied from interface: Recyclable
        Recycle the instance.
        Specified by:
        recycle in interface Recyclable