无法从 ReferenceQueue 中取出刚放进去的 Reference 元素，一直为 null

最近在读 TIJ4，在 P518 页持有引用一节，书中讲述了有关 java.lang.ref 包下的 Reference 类

ava 新手，查了些资料还是没有头绪，实在不行的话我换个 JDK 试下...
以下是原书部分样例代码

package sust.p600.p519; import java.lang.ref.Reference; import java.lang.ref.ReferenceQueue; import java.lang.ref.SoftReference; import java.lang.ref.WeakReference; import java.util.LinkedList; /** * Created by SunnyGrocery on 2019/11/17 18:05 */ public class References { private static ReferenceQueue<VeryBig> referenceQueue = new ReferenceQueue<>(); public static void main(String[] args) { int size = 10; LinkedList<SoftReference<VeryBig>> referenceLinkedList = new LinkedList<>(); for (int i = 0; i < size; i++) { referenceLinkedList.add(new SoftReference<>( new VeryBig("Soft:" + i), referenceQueue)); System.out.println("Just created:" + referenceLinkedList.getLast()); checkQueue(); } LinkedList<WeakReference<VeryBig>> referenceLinkedList1 = new LinkedList<>(); for (int i = 0; i < size; i++) { referenceLinkedList1.add(new WeakReference<>( new VeryBig("Weak:" + i), referenceQueue)); System.out.println("Just created:" + referenceLinkedList1.getLast()); checkQueue(); } } private static void checkQueue() { Reference<? extends VeryBig> reference = referenceQueue.poll(); if (reference != null) { System.out.println("In queue: " + reference.get()); } } } class VeryBig { private static final int SiZE = 10000; private long[] la = new long[SiZE]; private String ident; public VeryBig(String id) { ident = id; } @Override public String toString() { return "id = " + ident; } protected void finalize() { System.out.println("Finalizing:" + ident); } } 

输出

Just created:java.lang.ref.SoftReference@677327b6 Just created:java.lang.ref.SoftReference@14ae5a5 Just created:java.lang.ref.SoftReference@7f31245a Just created:java.lang.ref.SoftReference@6d6f6e28 Just created:java.lang.ref.SoftReference@135fbaa4 Just created:java.lang.ref.SoftReference@45ee12a7 Just created:java.lang.ref.SoftReference@330bedb4 Just created:java.lang.ref.SoftReference@2503dbd3 Just created:java.lang.ref.SoftReference@4b67cf4d Just created:java.lang.ref.SoftReference@7ea987ac Just created:java.lang.ref.WeakReference@12a3a380 Just created:java.lang.ref.WeakReference@29453f44 Just created:java.lang.ref.WeakReference@5cad8086 Just created:java.lang.ref.WeakReference@6e0be858 Just created:java.lang.ref.WeakReference@61bbe9ba Just created:java.lang.ref.WeakReference@610455d6 Just created:java.lang.ref.WeakReference@511d50c0 Just created:java.lang.ref.WeakReference@60e53b93 Just created:java.lang.ref.WeakReference@5e2de80c Just created:java.lang.ref.WeakReference@1d44bcfa 

结果中没有 checkQueue 中当 reference != null 时的输出 也就是说, referenceQueue.poll() 一直为空