Vector浅析

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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)

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