java判断对象是否还在被引用-不取消强引用，gc无法回收

 public static void main(String[] args) {
        Object obj = new Object();
        WeakReference<Object> weakRef = new WeakReference<>(obj);
        System.out.println(weakRef.get());
       
        System.gc(); // 提示垃圾回收器进行回收
        System.out.println(weakRef.get());
        // 判断对象是否被回收
        if (weakRef.get() == null) {
            System.out.println("对象已经被回收");
        } else {
            System.out.println("对象仍然存在");
        }
    }