Java的引用类型常用的四种方法

Object obj = new Object();

public class BeanA {
    @Override
    protected void finalize(){
        System.out.println("将对象从内存中清除出去");
    }
}

    public static void main(String[] args) throws ioException {
        BeanA a = new BeanA();
        a=null;
        System.gc();
        //防止gc线程结束后还未执行finalize方法
        System.in.read();
    }

public static void main(String[] args){
        SoftReference<byte[]> soft = new SoftReference<>(new byte[1024*1024*10]);
        System.out.println(soft.get());
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.gc();
        //注释掉下面这句两次get()方法都能获取到
        //byte[] bytes = new byte[1024 * 1024 * 15];
        System.out.println(soft.get());
    }

A a=new A();
SoftReference<A> soft =new SoftReference<>(a);

    public static void main(String[] args){
       WeakReference<byte[]> soft = new WeakReference<>(new byte[1024*1024*10]);
        System.out.println(soft.get());
        //通知JVM进行垃圾回收
        System.gc();
        try {
            Thread.sleep(500);
        } catch (InterruptedException e) {
            e.printStackTrace();
        }
        System.out.println(soft.get());
    }

        ReferenceQueue<Object> rq = new ReferenceQueue<>();
        Object obj = new Object();
        PhantomReference<Object> phantomReference = new PhantomReference<>(obj,rq);
        obj = null;
        System.out.println("Reference: "+phantomReference.get());
        System.gc();
        Reference<Object> r = (Reference<Object>)rq.poll();
        System.out.println("ReferenceQueue:  "+r);