Class Reference<T>

java.lang.Object
java.lang.ref.Reference<T>
Direct Known Subclasses:
PhantomReference, SoftReference, WeakReference
public abstract sealed class Reference<T> extends Object permits PhantomReference<T>, SoftReference<T>, WeakReference<T> (not exhaustive)
Abstract class which describes behavior common to all reference objects.
Since:
1.2

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    clear()
    Make the referent null.
    protected Object
    clone()
    This method will always throw CloneNotSupportedException.
    boolean
    enqueue()
    Force the reference object to be enqueued if it has been associated with a queue.
    T
    get()
    Return the referent of the reference object.
    boolean
    isEnqueued()
    Deprecated.
    Use ReferenceQueue or Reference.refersTo(null).
    static void
    reachabilityFence(Object ref)
    Used to keep the referenced object strongly reachable so that it is not reclaimable by garbage collection.
    final boolean
    refersTo(T target)
    Does this object refer to target?

    Methods declared in class Object

    equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
    Modifier and Type
    Method
    Description
    boolean
    equals(Object o)
    Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.
    protected void
    finalize()
    Deprecated, for removal: This API element is subject to removal in a future version.
    May cause performance issues, deadlocks and hangs.
    final Class<? extends Object>
    getClass()
    Answers the unique instance of java.lang.Class which represents the class of the receiver.
    int
    hashCode()
    Answers an integer hash code for the receiver.
    final void
    notify()
    Causes one thread which is waiting on the receiver to be made ready to run.
    final void
    notifyAll()
    Causes all threads which are waiting on the receiver to be made ready to run.
    String
    toString()
    Answers a string containing a concise, human-readable description of the receiver.
    final void
    wait()
    Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).
    final void
    wait(long time)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.
    final void
    wait(long time, int frac)
    Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

  • Method Details

    • clear

      public void clear()
      Make the referent null. This does not force the reference object to be enqueued.

    • enqueue

      public boolean enqueue()
      Force the reference object to be enqueued if it has been associated with a queue.
      Returns:
      true if Reference is enqueued, false otherwise.

    • get

      public T get()
      Return the referent of the reference object.
      Returns:
      the referent to which reference refers, or null if object has been cleared.

    • isEnqueued

      @Deprecated(since="16") public boolean isEnqueued()
      Deprecated.
      Use ReferenceQueue or Reference.refersTo(null).
      Return whether the reference object has been enqueued.
      Returns:
      true if Reference has been enqueued, false otherwise.

    • reachabilityFence

      public static void reachabilityFence(Object ref)
      Used to keep the referenced object strongly reachable so that it is not reclaimable by garbage collection.
      Parameters:
      ref - reference of the object.
      Since:
      9

    • clone

      protected Object clone() throws CloneNotSupportedException
      This method will always throw CloneNotSupportedException. A clone of this instance will not be returned since a Reference cannot be cloned. Workaround is to create a new Reference.
      Overrides:
      clone in class Object
      Returns:
      Object a shallow copy of this object.
      Throws:
      CloneNotSupportedException - always since a Reference cannot be cloned
      Since:
      11

    • refersTo

      public final boolean refersTo(T target)
      Does this object refer to target?
      Parameters:
      target - the candidate referent
      Returns:
      true if this object refers to target
      Since:
      16