package com.sunhang;
//: containers/References.java
// Demonstrates Reference objects
import java.lang.ref.*;
import java.util.*;
class VeryBig {
private static final int SIZE = 10000;
private long[] la = new long[SIZE];
private String ident;
public VeryBig(String id) { ident = id; }
public String toString() { return ident; }
protected void finalize() {
System.out.println("Finalizing " + ident);
}
}
public class References {
private static ReferenceQueue<VeryBig> rq =
new ReferenceQueue<VeryBig>();
public static void checkQueue() {
// Reference<? extends VeryBig> inq = rq.poll();
// if(inq != null)
// System.out.println("In queue: " + inq.get());
}
public static void main(String[] args) throws InterruptedException {
int size = 10;
// Or, choose size via the command line:
if(args.length > 0)
size = new Integer(args[0]);
LinkedList<SoftReference<VeryBig>> sa =
new LinkedList<SoftReference<VeryBig>>();
for(int i = 0; i < size; i++) {
sa.add(new SoftReference<VeryBig>(
new VeryBig("Soft " + i), rq));
System.out.println("Just created: " + sa.getLast());
checkQueue();
}
LinkedList<WeakReference<VeryBig>> wa =
new LinkedList<WeakReference<VeryBig>>();
for(int i = 0; i < size; i++) {
wa.add(new WeakReference<VeryBig>(
new VeryBig("Weak " + i), rq));
System.out.println("Just created: " + wa.getLast());
checkQueue();
}
SoftReference<VeryBig> s =
new SoftReference<VeryBig>(new VeryBig("Soft"));
WeakReference<VeryBig> w =
new WeakReference<VeryBig>(new VeryBig("Weak"));
System.gc();
LinkedList<PhantomReference<VeryBig>> pa =
new LinkedList<PhantomReference<VeryBig>>();
for(int i = 0; i < size; i++) {
pa.add(new PhantomReference<VeryBig>(
new VeryBig("Phantom " + i), rq));
System.out.println("Just created: " + pa.getLast());
checkQueue();
}
new Thread(){
@Override
public void run() {
try {
Thread.sleep(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
Reference<? extends VeryBig> inq = null;
int count = 0;
// while((inq = rq.poll()) != null){
// count ++;
// System.out.println("inq:" + inq.get() + " count:" + count + " " + inq.getClass().getSimpleName());
// }
synchronized (Reference.class){
try {
Reference.class.wait(2000);
} catch (InterruptedException e) {
e.printStackTrace();
}
}
System.out.println("again");
count = 0;
while((inq = rq.poll()) != null){
count ++;
System.out.println("inq:" + inq.get() + " count:" + count + " " + inq.getClass().getSimpleName());
}
}
}.start();
Thread.sleep(3000);
System.gc();
Thread.sleep(15000);
}
} /* (Execute to see output) *///:~
这段代码我认为会把PhantomReference加入到ReferenceQueue中，但是结果中表示并没有加入到队列中。这是为什么呢？有机会研究一下？结果如下：
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Finalizing Weak
Finalizing Weak 9
Finalizing Weak 8
Finalizing Weak 7
Finalizing Weak 6
Finalizing Weak 5
Finalizing Weak 4
Finalizing Weak 3
Finalizing Weak 2
Finalizing Weak 1
Finalizing Weak 0
Just created: [email protected]
Just created: [email protected]220b15
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Just created: [email protected]
Finalizing Phantom 4
Finalizing Phantom 5
Finalizing Phantom 7
Finalizing Phantom 6
Finalizing Phantom 0
Finalizing Phantom 1
Finalizing Phantom 2
Finalizing Phantom 3
Finalizing Phantom 9
Finalizing Phantom 8
again
inq:null count:1 WeakReference
inq:null count:2 WeakReference
inq:null count:3 WeakReference
inq:null count:4 WeakReference
inq:null count:5 WeakReference
inq:null count:6 WeakReference
inq:null count:7 WeakReference
inq:null count:8 WeakReference
inq:null count:9 WeakReference
inq:null count:10 WeakReference