2017-07-29 12:59:14
一、简介
1、Vector继承关系
2、Vector类扩容
Vector类的实现和ArrayList极其相似，都使用数组存储元素，但是扩容策略不一样，ArrayList基本是按照1.5倍的思路扩容，Vector是按照创建Vector对象时设置的capacityIncrement值递增的，如果该值没有设置或者为0，则直接Double，如下：
3、Vector的线程安全性
Vector号称是线程安全的，它的安全性来自于几乎给每个方法都添加了synchronized关键字，由于锁对象是当前对象，只要有一个线程在执行某一个加锁的方法，也就是获得到当前对象这个锁对象，其他线程基本都不能再使用这个Vector对象了...这是一种很残暴的设计，估计这可能是synchronized刚出来之时，JDK团队的一时兴奋之作吧~
举几个例子：
即便是有一些方法没有直接加synchronized关键字，至少它所调用的方法都是加了的。
4、Stack
Stack继承自Vector，提供了pop、push、peek、search等栈的特殊操作，源码如下：
1 package java.util;
2
3 /**
4 * The <code>Stack</code> class represents a last-in-first-out
5 * (LIFO) stack of objects. It extends class <tt>Vector</tt> with five
6 * operations that allow a vector to be treated as a stack. The usual
7 * <tt>push</tt> and <tt>pop</tt> operations are provided, as well as a
8 * method to <tt>peek</tt> at the top item on the stack, a method to test
9 * for whether the stack is <tt>empty</tt>, and a method to <tt>search</tt>
10 * the stack for an item and discover how far it is from the top.
11 * <p>
12 * When a stack is first created, it contains no items.
13 *
14 * <p>A more complete and consistent set of LIFO stack operations is
15 * provided by the {@link Deque} interface and its implementations, which
16 * should be used in preference to this class. For example:
17 * <pre> {@code
18 * Deque<Integer> stack = new ArrayDeque<Integer>();}</pre>
19 *
20 * @author Jonathan Payne
21 * @since JDK1.0
22 */
23 public
24 class Stack<E> extends Vector<E> {
25 /**
26 * Creates an empty Stack.
27 */
28 public Stack() {
29 }
30
31 /**
32 * Pushes an item onto the top of this stack. This has exactly
33 * the same effect as:
34 * <blockquote><pre>
35 * addElement(item)</pre></blockquote>
36 *
37 * @param item the item to be pushed onto this stack.
38 * @return the <code>item</code> argument.
39 * @see java.util.Vector#addElement
40 */
41 public E push(E item) {
42 addElement(item);
43
44 return item;
45 }
46
47 /**
48 * Removes the object at the top of this stack and returns that
49 * object as the value of this function.
50 *
51 * @return The object at the top of this stack (the last item
52 * of the <tt>Vector</tt> object).
53 * @throws EmptyStackException if this stack is empty.
54 */
55 public synchronized E pop() {
56 E obj;
57 int len = size();
58
59 obj = peek();
60 removeElementAt(len - 1);
61
62 return obj;
63 }
64
65 /**
66 * Looks at the object at the top of this stack without removing it
67 * from the stack.
68 *
69 * @return the object at the top of this stack (the last item
70 * of the <tt>Vector</tt> object).
71 * @throws EmptyStackException if this stack is empty.
72 */
73 public synchronized E peek() {
74 int len = size();
75
76 if (len == 0)
77 throw new EmptyStackException();
78 return elementAt(len - 1);
79 }
80
81 /**
82 * Tests if this stack is empty.
83 *
84 * @return <code>true</code> if and only if this stack contains
85 * no items; <code>false</code> otherwise.
86 */
87 public boolean empty() {
88 return size() == 0;
89 }
90
91 /**
92 * Returns the 1-based position where an object is on this stack.
93 * If the object <tt>o</tt> occurs as an item in this stack, this
94 * method returns the distance from the top of the stack of the
95 * occurrence nearest the top of the stack; the topmost item on the
96 * stack is considered to be at distance <tt>1</tt>. The <tt>equals</tt>
97 * method is used to compare <tt>o</tt> to the
98 * items in this stack.
99 *
100 * @param o the desired object.
101 * @return the 1-based position from the top of the stack where
102 * the object is located; the return value <code>-1</code>
103 * indicates that the object is not on the stack.
104 */
105 public synchronized int search(Object o) {
106 int i = lastIndexOf(o);
107
108 if (i >= 0) {
109 return size() - i;
110 }
111 return -1;
112 }
113
114 /** use serialVersionUID from JDK 1.0.2 for interoperability */
115 private static final long serialVersionUID = 1224463164541339165L;
116 }
5、结尾
Vector和ArrayList的异同：
1、扩容策略不同；
2、线程安全的；
3、提供了一些独特的如removeElement()之类的方法；
4、其他方法的实现与ArrayList几乎是一致的，毕竟都是对数组的操作；
5、忽略这个类即可；
时间： 2024-10-11 08:25:42