import java.lang.ref.ReferenceQueue;
import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.lang.ref.PhantomReference;
import java.util.WeakHashMap;
public class References {
public static void main(String[] args) {
Object a = new Object();
Object b = new Object();
Object c = new Object();
Object d = new Object();
Object e = new Object();
Object f = new Object();
ReferenceQueue q = new ReferenceQueue();
Reference ar = new WeakReference(a);
Reference br = new WeakReference(b, q);
Reference cr = new WeakReference(c, q);
Reference dr = new PhantomReference(d, q);
Reference er = new MyReference(e, q, "foo");
WeakHashMap<Key,Object> map = new WeakHashMap();
map.put(new Key("foo"), f);
a = b = c = d = e = cr = null;
System.out.println("a: " + ar.get());
System.out.println("b: " + br.get());
System.out.println("d: " + dr.get());
System.out.println("e: " + er.get());
System.out.println("f: " + map.get(new Key("foo")));
System.gc();
System.out.println("a: " + ar.get());
System.out.println("b: " + br.get());
System.out.println("d: " + dr.get());
System.out.println("e: " + er.get());
System.out.println("f: " + map.get(new Key("foo")));
for (Reference r = q.poll(); r != null; r = q.poll()) {
System.out.println("polled: " + r.get());
}
}
private static class MyReference extends WeakReference {
private final Object foo;
public MyReference(Object target, ReferenceQueue queue, Object foo) {
super(target, queue);
this.foo = foo;
}
}
private static class Key {
private final String name;
public Key(String name) {
this.name = name;
}
public int hashCode() {
return name.hashCode();
}
public boolean equals(Object o) {
return o instanceof Key && ((Key) o).name.equals(name);
}
}
}