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/*
* Copyright (C) 2005-2015 Schlichtherle IT Services.
* All rights reserved. Use is subject to license terms.
*/
package net.java.truecommons.shed;
import java.lang.ref.PhantomReference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
import javax.annotation.CheckForNull;
/**
* A link has a nullable {@link #get() target} property.
* This interface is useful if a class is decorating or adapting another class
* and access to the decorated or adapted object should be provided as part of
* the public API of the decorating or adapting class.
*
* @param The type of the target.
* @author Christian Schlichtherle
*/
public interface Link {
/**
* Returns the target of this link.
*
* The returned object reference may be {@code null} subject to the terms
* and conditions of sub-interfaces or implementations.
*
* @return The target of this link.
*/
@CheckForNull T get();
/**
* A factory for links which defines the terms and conditions for clearing
* their target.
*/
@SuppressWarnings("PublicInnerClass")
enum Type {
/** This reference type never clears the target of a link. */
STRONG {
@Override
Link newLink(@CheckForNull T target, ReferenceQueue queue) {
return new Strong<>(target);
}
},
/**
* This reference type clears the target of a link according to the
* terms and conditions for a {@link SoftReference}.
*/
SOFT {
@Override
Link newLink(@CheckForNull T target, ReferenceQueue queue) {
return new Soft<>(target, queue);
}
},
/**
* This reference type clears the target of a link according to the
* terms and conditions for a {@link WeakReference}.
*/
WEAK {
@Override
Link newLink(@CheckForNull T target, ReferenceQueue queue) {
return new Weak<>(target, queue);
}
},
/**
* This reference type clears the target of a link according to the
* terms and conditions for a {@link PhantomReference}.
*/
PHANTOM {
@Override
public Link newLink(@CheckForNull T target, ReferenceQueue queue) {
return new Phantom<>(target, queue);
}
};
/** Returns a new typed link to the given nullable target. */
abstract Link newLink(@CheckForNull T target, @CheckForNull ReferenceQueue queue);
/** Returns a new typed link to the given nullable target. */
public Link newLink(@CheckForNull T target) {
return newLink(target, null);
}
/** A strong reference. */
private static final class Strong implements Link {
private final @CheckForNull T target;
Strong(final @CheckForNull T target) {
this.target = target;
}
@Override
public T get() {
return target;
}
@Override
public String toString() {
return String.format("%s[target=%s]",
getClass().getName(),
get());
}
}
/** Adapts its subclass to the {@link Link} interface. */
private static final class Soft extends SoftReference
implements Link {
Soft(T target, ReferenceQueue queue) {
super(target, queue);
}
@Override
public String toString() {
return String.format("%s[target=%s]",
getClass().getName(),
get());
}
}
/** Adapts its subclass to the {@link Link} interface. */
private static final class Weak extends WeakReference
implements Link {
Weak(T target, ReferenceQueue queue) {
super(target, queue);
}
@Override
public String toString() {
return String.format("%s[target=%s]",
getClass().getName(),
get());
}
}
/** Adapts its subclass to the {@link Link} interface. */
private static final class Phantom extends PhantomReference
implements Link {
Phantom(T target, ReferenceQueue queue) {
super(target, queue);
}
@Override
public String toString() {
return String.format("%s[target=%s]",
getClass().getName(),
get());
}
}
}
}