Mega Code Archive
Demonstrates Reference objects
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// : c11:References.java
// Demonstrates Reference objects
// From 'Thinking in Java, 3rd ed.' (c) Bruce Eckel 2002
// www.BruceEckel.com. See copyright notice in CopyRight.txt.
import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;
import java.lang.ref.SoftReference;
import java.lang.ref.WeakReference;
class VeryBig {
private static final int SZ = 10000;
private double[] d = new double[SZ];
private String ident;
public VeryBig(String id) {
ident = id;
}
public String toString() {
return ident;
}
public void finalize() {
System.out.println("Finalizing " + ident);
}
}
public class References {
private static ReferenceQueue rq = new ReferenceQueue();
public static void checkQueue() {
Object inq = rq.poll();
if (inq != null)
System.out
.println("In queue: " + (VeryBig) ((Reference) inq).get());
}
public static void main(String[] args) {
int size = 10;
// Or, choose size via the command line:
if (args.length > 0)
size = Integer.parseInt(args[0]);
SoftReference[] sa = new SoftReference[size];
for (int i = 0; i < sa.length; i++) {
sa[i] = new SoftReference(new VeryBig("Soft " + i), rq);
System.out.println("Just created: " + (VeryBig) sa[i].get());
checkQueue();
}
WeakReference[] wa = new WeakReference[size];
for (int i = 0; i < wa.length; i++) {
wa[i] = new WeakReference(new VeryBig("Weak " + i), rq);
System.out.println("Just created: " + (VeryBig) wa[i].get());
checkQueue();
}
SoftReference s = new SoftReference(new VeryBig("Soft"));
WeakReference w = new WeakReference(new VeryBig("Weak"));
System.gc();
PhantomReference[] pa = new PhantomReference[size];
for (int i = 0; i < pa.length; i++) {
pa[i] = new PhantomReference(new VeryBig("Phantom " + i), rq);
System.out.println("Just created: " + (VeryBig) pa[i].get());
checkQueue();
}
}
} ///:~
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