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package sun.misc;
import java.lang.ref.SoftReference;
A "Ref" is an indirect reference to an object that the garbage collector
knows about. An application should override the reconstitute() method with one
that will construct the object based on information in the Ref, often by
reading from a file. The get() method retains a cache of the result of the last call to
reconstitute() in the Ref. When space gets tight, the garbage collector
will clear old Ref cache entries when there are no other pointers to the
object. In normal usage, Ref will always be subclassed. The subclass will add the
instance variables necessary for the reconstitute() method to work. It will also add a
constructor to set them up, and write a version of reconstitute().
See Also: - SoftReference
Deprecated: This class has been replaced by
java.util.SoftReference.
/**
* A "Ref" is an indirect reference to an object that the garbage collector
* knows about. An application should override the reconstitute() method with one
* that will construct the object based on information in the Ref, often by
* reading from a file. The get() method retains a cache of the result of the last call to
* reconstitute() in the Ref. When space gets tight, the garbage collector
* will clear old Ref cache entries when there are no other pointers to the
* object. In normal usage, Ref will always be subclassed. The subclass will add the
* instance variables necessary for the reconstitute() method to work. It will also add a
* constructor to set them up, and write a version of reconstitute().
*
* @deprecated This class has been replaced by
* <code>java.util.SoftReference</code>.
*
* @see java.util.SoftReference
*
*/
@Deprecated
public abstract class Ref {
private SoftReference soft = null;
Returns a pointer to the object referenced by this Ref. If the object
has been thrown away by the garbage collector, it will be
reconstituted. This method does everything necessary to ensure that the garbage
collector throws things away in Least Recently Used(LRU) order. Applications should
never override this method. The get() method effectively caches calls to
reconstitute().
/**
* Returns a pointer to the object referenced by this Ref. If the object
* has been thrown away by the garbage collector, it will be
* reconstituted. This method does everything necessary to ensure that the garbage
* collector throws things away in Least Recently Used(LRU) order. Applications should
* never override this method. The get() method effectively caches calls to
* reconstitute().
*/
public synchronized Object get() {
Object t = check();
if (t == null) {
t = reconstitute();
setThing(t);
}
return t;
}
Returns a pointer to the object referenced by this Ref by
reconstituting it from some external source (such as a file). This method should not
bother with caching since the method get() will deal with that.
In normal usage, Ref will always be subclassed. The subclass will add
the instance variables necessary for reconstitute() to work. It will
also add a constructor to set them up, and write a version of
reconstitute().
/**
* Returns a pointer to the object referenced by this Ref by
* reconstituting it from some external source (such as a file). This method should not
* bother with caching since the method get() will deal with that.
* <p>
* In normal usage, Ref will always be subclassed. The subclass will add
* the instance variables necessary for reconstitute() to work. It will
* also add a constructor to set them up, and write a version of
* reconstitute().
*/
public abstract Object reconstitute();
Flushes the cached object. Forces the next invocation of get() to
invoke reconstitute().
/**
* Flushes the cached object. Forces the next invocation of get() to
* invoke reconstitute().
*/
public synchronized void flush() {
SoftReference s = soft;
if (s != null) s.clear();
soft = null;
}
Sets the thing to the specified object.
Params: - thing – the specified object
/**
* Sets the thing to the specified object.
* @param thing the specified object
*/
public synchronized void setThing(Object thing) {
flush();
soft = new SoftReference(thing);
}
Checks to see what object is being pointed at by this Ref and returns it.
/**
* Checks to see what object is being pointed at by this Ref and returns it.
*/
public synchronized Object check() {
SoftReference s = soft;
if (s == null) return null;
return s.get();
}
Constructs a new Ref.
/**
* Constructs a new Ref.
*/
public Ref() { }
Constructs a new Ref that initially points to thing.
/**
* Constructs a new Ref that initially points to thing.
*/
public Ref(Object thing) {
setThing(thing);
}
}