Vector

线程安全的集合，方法都带锁所以线程安全，但是效率慢

1.add

 public synchronized boolean add(E e) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
}

2.get

 public synchronized E get(int index) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        return elementData(index);
 }

3.remove

 public synchronized E remove(int index) {
        modCount++;
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);
        E oldValue = elementData(index);

        int numMoved = elementCount - index - 1;
        if (numMoved > 0)
            System.arraycopy(elementData, index+1, elementData, index,
                             numMoved);
        elementData[--elementCount] = null; // Let gc do its work

        return oldValue;
 }