Module java.base
Package java.lang.ref

Class Reference<T>

java.lang.Object
java.lang.ref.Reference<T>
Direct Known Subclasses:
PhantomReference, SoftReference, WeakReference

public abstract class Reference<T> extends Object
Abstract class which describes behavior common to all reference objects.
Since:
1.2
  • Method Summary

    Modifier and Type
    Method
    Description
    void
    Make the referent null.
    protected Object
    This method will always throw CloneNotSupportedException.
    boolean
    Force the reference object to be enqueued if it has been associated with a queue.
    get()
    Return the referent of the reference object.
    boolean
    Deprecated.
    Use ReferenceQueue or Reference.refersTo(null).
    static void
    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 java.lang.Object

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