Reference (Java Platform SE 8 ) (original) (raw)

• java.lang.Object

• • java.lang.ref.Reference

• Direct Known Subclasses:
  PhantomReference, SoftReference, WeakReference

public abstract class Reference
extends Object
Abstract base class for reference objects. This class defines the operations common to all reference objects. Because reference objects are implemented in close cooperation with the garbage collector, this class may not be subclassed directly.
Since:
1.2

• • Method Summary

  All Methods Instance Methods Concrete Methods

  Modifier and Type	Method	Description
  void	clear()	Clears this reference object.
  protected Object	clone()	Throws CloneNotSupportedException.
  boolean	enqueue()	Clears this reference object and adds it to the queue with which it is registered, if any.
  T	get()	Returns this reference object's referent.
  boolean	isEnqueued()	Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector.

     * ### Methods inherited from class java.lang.[Object](../../../java/lang/Object.html "class in java.lang")  
     `[equals](../../../java/lang/Object.html#equals-java.lang.Object-), [finalize](../../../java/lang/Object.html#finalize--), [getClass](../../../java/lang/Object.html#getClass--), [hashCode](../../../java/lang/Object.html#hashCode--), [notify](../../../java/lang/Object.html#notify--), [notifyAll](../../../java/lang/Object.html#notifyAll--), [toString](../../../java/lang/Object.html#toString--), [wait](../../../java/lang/Object.html#wait--), [wait](../../../java/lang/Object.html#wait-long-), [wait](../../../java/lang/Object.html#wait-long-int-)`

• • Method Detail

     * #### get  
     public [T](../../../java/lang/ref/Reference.html "type parameter in Reference") get()  
     Returns this reference object's referent. If this reference object has been cleared, either by the program or by the garbage collector, then this method returns `null`.  
     Returns:  
     The object to which this reference refers, or`null` if this reference object has been cleared  
     * #### clear  
     public void clear()  
     Clears this reference object. Invoking this method will not cause this object to be enqueued.  
      This method is invoked only by Java code; when the garbage collector clears references it does so directly, without invoking this method.  
     * #### isEnqueued  
     public boolean isEnqueued()  
     Tells whether or not this reference object has been enqueued, either by the program or by the garbage collector. If this reference object was not registered with a queue when it was created, then this method will always return `false`.  
     Returns:  
     `true` if and only if this reference object has been enqueued  
     * #### enqueue  
     public boolean enqueue()  
     Clears this reference object and adds it to the queue with which it is registered, if any.  
      This method is invoked only by Java code; when the garbage collector enqueues references it does so directly, without invoking this method.  
     Returns:  
     `true` if this reference object was successfully enqueued; `false` if it was already enqueued or if it was not registered with a queue when it was created  
     * #### clone  
     protected [Object](../../../java/lang/Object.html "class in java.lang") clone()  
                     throws [CloneNotSupportedException](../../../java/lang/CloneNotSupportedException.html "class in java.lang")  
     Throws [CloneNotSupportedException](../../../java/lang/CloneNotSupportedException.html "class in java.lang"). A `Reference` cannot be meaningfully cloned. Construct a new `Reference` instead.  
     Overrides:  
     `[clone](../../../java/lang/Object.html#clone--)` in class `[Object](../../../java/lang/Object.html "class in java.lang")`  
     API Note:  
     This method is defined in Java SE 8 Maintenance Release 4.  
     Returns:  
     never returns normally  
     Throws:  
     `[CloneNotSupportedException](../../../java/lang/CloneNotSupportedException.html "class in java.lang")` \- always  
     Since:  
     8  
     See Also:  
     [Cloneable](../../../java/lang/Cloneable.html "interface in java.lang")

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