Vector与ArrayList很像，主要区别在于Vector是线程安全的。
Vector的类声明:
*
As of the Java 2 platform v1.2, this class was retrofitted to
* implement the {@link List} interface, making it a member of the
*
* Java Collections Framework. Unlike the new collection
* implementations, {@code Vector} is synchronized. If a thread-safe
* implementation is not needed, it is recommended to use {@link
* ArrayList} in place of {@code Vector}.
阅读源码后发现，Vector是通过给所有的外部类加上synchronized来实现线程安全的。这种实现方式很简单，但由于synchronized是对this加锁，所以当需要同时一个对象的多个方法时，效率就会很低。
另外，查看iterator的源码
/**
* Returns an iterator over the elements in this list in proper sequence.
*
* <p>The returned iterator is <a href="#fail-fast"><i>fail-fast</i></a>.
*
* @return an iterator over the elements in this list in proper sequence
*/
public synchronized Iterator<E> iterator() {
return new Itr();
}
可以发现，在返回遍历对象后，就已经退出了锁，如果修改了对象之后，再去遍历，则会抛出ConcurrentModificationException异常.
Vector<String> vector = new Vector<String>();
vector.add("abc");
Iterator<String> ite = vector.iterator();
vector.add("bcd");
while (ite.hasNext()) {
System.out.println(ite.next());
}
运行结果：
Exception in thread "main" java.util.ConcurrentModificationException
at java.util.Vector$Itr.checkForComodification(Vector.java:1184)
at java.util.Vector$Itr.next(Vector.java:1137)
at com.showstone.containerresearch.list.VectorResearch.main(VectorResearch.java:14)