ArrayList al = new ArrayList();
    Connections.syncchronizedList(al);

HashMap map = new HashMap<>();
    Map map1 = Collections.synchronizedMap(map);

/**
     * Appends the specified element to the end of this list.
     *
     * @param e element to be appended to this list
     * @return {@code true} (as specified by {@link Collection#add})
     */
    public boolean add(E e) {
        final ReentrantLock lock = this.lock;  //获取锁ReentrantLock
        lock.lock();
        try {
            Object[] elements = getArray();  // 获取CopyOnWriteArrayList内部维护的数组
            int len = elements.length;      
            Object[] newElements = Arrays.copyOf(elements, len + 1);  // 复制该数组到 newElements数组里面  并扩容
            newElements[len] = e;  //在数组最后添加新的元素
            setArray(newElements); //让替换掉原来的数组 
            return true;    //添加成功
        } finally {
            lock.unlock();
        }
    }
  /**
     * {@inheritDoc}
     *
     * @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public E get(int index) {
        return get(getArray(), index);
    }

public E remove(int index) {
    final ReentrantLock lock = this.lock;
    lock.lock();
    try {
        Object[] elements = getArray();
        int len = elements.length;
        E oldValue = get(elements, index);
        int numMoved = len - index - 1;
        if (numMoved == 0) //移除最后一个
            setArray(Arrays.copyOf(elements, len - 1)); 
        else {      // 移除其它的,当前元素后面的需要往前移动
            Object[] newElements = new Object[len - 1];
            System.arraycopy(elements, 0, newElements, 0, index);
            System.arraycopy(elements, index + 1, newElements, index,
                             numMoved);
            setArray(newElements);
        }
        return oldValue;  // 移除谁,返回谁
    } finally {
        lock.unlock();
    }
}

Set<Object> set = Collections.synchronizedSet(new HashSet<>());

Collections.synchronizedMap();

/**
 * Inserts the specified element at the tail of this queue.
 * As the queue is unbounded, this method will never return {@code false}.
 *
 * @return {@code true} (as specified by {@link Queue#offer})
 * @throws NullPointerException if the specified element is null
 */
public boolean offer(E e) {
    checkNotNull(e);  // 检查新添加的内容是否为空
    final Node<E> newNode = new Node<E>(e); // 将其放入新节点
    for (Node<E> t = tail, p = t;;) {  // 整个一个for循环, 循环遍历链表,寻找适当的位置,插入新节点
        Node<E> q = p.next;
        if (q == null) {
            // p is last node
            if (p.casNext(null, newNode)) {
                // Successful CAS is the linearization point
                // for e to become an element of this queue,
                // and for newNode to become "live".
                if (p != t) // hop two nodes at a time
                    casTail(t, newNode);  // Failure is OK. //可以看到,在这种会出现线程安全性问题的地方,使用的是cas进行操作,保证了线程的安全性
                return true;
            }
            // Lost CAS race to another thread; re-read next
        }
        else if (p == q)
            // We have fallen off list.  If tail is unchanged, it
            // will also be off-list, in which case we need to
            // jump to head, from which all live nodes are always
            // reachable.  Else the new tail is a better bet.
            p = (t != (t = tail)) ? t : head;
        else
            // Check for tail updates after two hops.
            p = (p != t && t != (t = tail)) ? t : q;
    }
}
    // 可以看到,casXXX 底层使用的是UNSAFE实现(保证线程的安全性)    
       private boolean casTail(Node<E> cmp, Node<E> val) {
        return UNSAFE.compareAndSwapObject(this, tailOffset, cmp, val);
    }
    private boolean casHead(Node<E> cmp, Node<E> val) {
        return UNSAFE.compareAndSwapObject(this, headOffset, cmp, val);
    }

public E poll() {
    restartFromHead:
    for (;;) {
        for (Node<E> h = head, p = h, q;;) {
            E item = p.item;
            if (item != null && p.casItem(item, null)) {
                // Successful CAS is the linearization point
                // for item to be removed from this queue.
                if (p != h) // hop two nodes at a time
                    updateHead(h, ((q = p.next) != null) ? q : p);
                return item;
            }
            else if ((q = p.next) == null) {
                updateHead(h, p);
                return null;
            }
            else if (p == q)
                continue restartFromHead;
            else
                p = q;
        }
    }