JVM19——引用队列

如果软引用所指的对象已经是null了，没有必要再把这四个软引用保留在list集合中。可以配合引用队列来完成软引用的回收。

  public static void soft() {
        // list --> SoftReference --> byte[]
        List<SoftReference<byte[]>> list = new ArrayList<>();
        ReferenceQueue<byte[]> referenceQueue = new ReferenceQueue<>();
        for (int i = 0; i < 5; i++) {
            SoftReference<byte[]> ref = new SoftReference<>(new byte[_4MB], referenceQueue);
            System.out.println(ref.get());
            list.add(ref);
            System.out.println(list.size());

        }

        Reference<? extends byte[]> poll = referenceQueue.poll();
        while (poll != null) {
            list.remove(poll);
            poll = referenceQueue.poll();
        }
        System.out.println("循环结束：" + list.size());
        for (SoftReference<byte[]> ref : list) {
            System.out.println(ref.get());
        }
    }

结果如下。

[B@7f31245a
1
[B@6d6f6e28
2
[B@135fbaa4
3
[B@45ee12a7
4
[B@330bedb4
5
循环结束：1
[B@330bedb4

Process finished with exit code 0