ArrayList：线程不安全，所有的方法都未加锁，效率最高

  public boolean add(E e) {ensureCapacityInternal(size + 1);  // Increments modCount!!elementData[size++] = e;return true;}

Vector：线程安全，所有的方法加锁，且加锁在方法上，效率最低（方法内部存在逻辑处理）

public synchronized boolean add(E e) {modCount++;ensureCapacityHelper(elementCount + 1);elementData[elementCount++] = e;return true;}public synchronized void insertElementAt(E obj, int index) {modCount++;if (index > elementCount) {throw new ArrayIndexOutOfBoundsException(index+ " > " + elementCount);}ensureCapacityHelper(elementCount + 1);System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);elementData[index] = obj;elementCount++;}

Collections.synchronizedList(new ArrayList)：读写删除加锁，且加锁在代码块上，效率较好，遍历未加锁，可以根据实际业务需求，自行决定是否加锁

 public E get(int index) {synchronized (mutex) {return list.get(index);}}public E set(int index, E element) {synchronized (mutex) {return list.set(index, element);}}public void add(int index, E element) {synchronized (mutex) {list.add(index, element);}}public E remove(int index) {synchronized (mutex) {return list.remove(index);}}public int indexOf(Object o) {synchronized (mutex) {return list.indexOf(o);}}public int lastIndexOf(Object o) {synchronized (mutex) {return list.lastIndexOf(o);}}public boolean addAll(int index, Collection<? extends E> c) {synchronized (mutex) {return list.addAll(index, c);}}public ListIterator<E> listIterator() {return list.listIterator(); // Must be manually synched by user}public ListIterator<E> listIterator(int index) {return list.listIterator(index); // Must be manually synched by user}

CopyOnWriteArrayList：读未加锁，写使用CAS自旋锁，先复制原数组，修改复制的数组，之后把复制数组重新复制给原地址（当数组过大时，复制效率极低），并发过多，CAS碰撞过多，也会影响性能，读取数据是原数组，所以如果add方法还未执行到setArray方法，读取的数据就是原来的数据。

public boolean add(E e) {final ReentrantLock lock = this.lock;lock.lock();try {Object[] elements = getArray();int len = elements.length;Object[] newElements = Arrays.copyOf(elements, len + 1);newElements[len] = e;setArray(newElements);return true;} finally {lock.unlock();}}