Hướng dẫn và ví dụ Java PhantomReference

PhantomReference​(T innerObject, ReferenceQueue<? super T> queue)

ReferenceQueue<AnyObject> queue = new ReferenceQueue<>();

AnyObject innerObject = new AnyObject("Obj1");

PhantomReference phantomRef = new PhantomReference(innerObject, queue);

// Methods inherited from parent.
public T get()  
public void clear()  
public boolean isEnqueued()  
public boolean enqueue()

PhantomReference phantomRef = new PhantomReference(innerObject, queue);

package org.o7planning.phantomreference.ex;

public class VideoProcessor {
    private String video;

    public VideoProcessor(String video)  {
        this.video = video;
        System.out.println("\nNew VideoProcessor: " + this.video);
    }

    public void process() {
        System.out.println("   >>> Processing video: " + this.video);
        try {
            Thread.sleep(2000);
        } catch (InterruptedException e) { }
        System.out.println("   >>> Completed processing video: " + this.video);
    }
    
    // !IMPORTANT: Do not override finalize() method.
    //  (Java9+: If you override this method, PhantomReference will not work!!)
    //    @Override
    //    protected void finalize() throws Throwable {
    //        System.out.println("VideoProcessor is being removed from memory\n");
    //        super.finalize();
    //    }
}

package org.o7planning.phantomreference.ex;

import java.lang.ref.PhantomReference;
import java.lang.ref.Reference;
import java.lang.ref.ReferenceQueue;

public class PhantomReferenceEx1 {

    public static void main(String[] args) {

        String[] videos = new String[] { "video1.mp4", "video2.mp4", "video3.mp4" };

        ReferenceQueue<VideoProcessor> queue = new ReferenceQueue<VideoProcessor>();

        for (String video : videos) {
            VideoProcessor videoProcessor = new VideoProcessor(video);

            PhantomReference<VideoProcessor> phantomRef = new PhantomReference<>(videoProcessor, queue);
            videoProcessor.process();

            videoProcessor = null;
            // Call GC:
            System.gc();

            while (true) {
                boolean isEnqueued = phantomRef.isEnqueued();
                System.out.println(" phantomRef.isEnqueued: " + isEnqueued);
            
                if (!isEnqueued) {
                    try {
                        Thread.sleep(1000);
                    } catch (InterruptedException e) {
                    }
                    continue;
                }
                break;
            }
        }
        System.out.println("\nObjects in the queue:");
        Reference<? extends VideoProcessor> ref= null;
        
        while((ref = queue.poll())!= null)  {
            System.out.println(ref);
        }
    }
}