92 lines
2.9 KiB
Java
92 lines
2.9 KiB
Java
// collectiontopics/References.java
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// (c)2020 MindView LLC: see Copyright.txt
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// We make no guarantees that this code is fit for any purpose.
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// Visit http://OnJava8.com for more book information.
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// Demonstrates Reference objects
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import java.lang.ref.*;
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import java.util.*;
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class VeryBig {
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private static final int SIZE = 10000;
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private long[] la = new long[SIZE];
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private String ident;
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VeryBig(String id) { ident = id; }
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@Override
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public String toString() { return ident; }
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@Override
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protected void finalize() {
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System.out.println("Finalizing " + ident);
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}
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}
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public class References {
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private static ReferenceQueue<VeryBig> rq =
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new ReferenceQueue<>();
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public static void checkQueue() {
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Reference<? extends VeryBig> inq = rq.poll();
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if(inq != null)
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System.out.println("In queue: " + inq.get());
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}
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public static void main(String[] args) {
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int size = 10;
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// Or, choose size via the command line:
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if(args.length > 0)
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size = Integer.valueOf(args[0]);
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LinkedList<SoftReference<VeryBig>> sa =
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new LinkedList<>();
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for(int i = 0; i < size; i++) {
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sa.add(new SoftReference<>(
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new VeryBig("Soft " + i), rq));
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System.out.println(
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"Just created: " + sa.getLast());
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checkQueue();
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}
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LinkedList<WeakReference<VeryBig>> wa =
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new LinkedList<>();
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for(int i = 0; i < size; i++) {
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wa.add(new WeakReference<>(
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new VeryBig("Weak " + i), rq));
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System.out.println(
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"Just created: " + wa.getLast());
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checkQueue();
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}
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SoftReference<VeryBig> s =
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new SoftReference<>(new VeryBig("Soft"));
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WeakReference<VeryBig> w =
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new WeakReference<>(new VeryBig("Weak"));
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System.gc();
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LinkedList<PhantomReference<VeryBig>> pa =
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new LinkedList<>();
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for(int i = 0; i < size; i++) {
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pa.add(new PhantomReference<>(
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new VeryBig("Phantom " + i), rq));
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System.out.println(
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"Just created: " + pa.getLast());
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checkQueue();
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}
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}
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}
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/* Output: (First and Last 10 Lines)
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Just created: java.lang.ref.SoftReference@15db9742
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Just created: java.lang.ref.SoftReference@6d06d69c
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Just created: java.lang.ref.SoftReference@7852e922
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Just created: java.lang.ref.SoftReference@4e25154f
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Just created: java.lang.ref.SoftReference@70dea4e
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Just created: java.lang.ref.SoftReference@5c647e05
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Just created: java.lang.ref.SoftReference@33909752
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Just created: java.lang.ref.SoftReference@55f96302
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Just created: java.lang.ref.SoftReference@3d4eac69
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Just created: java.lang.ref.SoftReference@42a57993
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...________...________...________...________...
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Just created: java.lang.ref.PhantomReference@45ee12a7
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In queue: null
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Just created: java.lang.ref.PhantomReference@330bedb4
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In queue: null
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Just created: java.lang.ref.PhantomReference@2503dbd3
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In queue: null
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Just created: java.lang.ref.PhantomReference@4b67cf4d
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In queue: null
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Just created: java.lang.ref.PhantomReference@7ea987ac
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In queue: null
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*/
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