Java 集合框架源码解读之Vector

1：Vector简介

Java中Vector类是允许不同类型元素共存的变长数组，Java.util.Vector提供了向量（Vector）类以实现类似动态数组的功能。在Java语言中是没有指针概念的，但如果能正确灵活地使用指针又确实可以大大提高程序的质量，比如在C、C++中所谓“动态数组”一般都由指针来实现。为了弥补这点缺陷，Java提供了丰富的类库来方便编程者使用，Vector类便是其中之一。事实上，灵活使用数组也可完成向量类的功能，向量类中提供的大量方法也大大方便了用户的使用。
Vector 作为一款古老的集合工具（since JDK1.0），从 JDK1.2 开始被改造成 List 的实现加入集合框架。它的实现基本与ArrayList相同，主要区别在于它是一个线程安全的集合。

2：属性和构造方法

   /** * The array buffer into which the components of the vector are * stored. The capacity of the vector is the length of this array buffer, * and is at least large enough to contain all the vector's elements. * * <p>Any array elements following the last element in the Vector are null. * * @serial * 存放元素的数组 */ protected Object[] elementData; /** * The number of valid components in this {@code Vector} object. * Components {@code elementData[0]} through * {@code elementData[elementCount-1]} are the actual items. * * @serial * 数组中实际元素数量 */ protected int elementCount; /** * The amount by which the capacity of the vector is automatically * incremented when its size becomes greater than its capacity.  If * the capacity increment is less than or equal to zero, the capacity * of the vector is doubled each time it needs to grow. * * @serial * 每次扩容的大小，如果为 0，每次扩容为原来的两倍 */ protected int capacityIncrement; /** * Constructs an empty vector with the specified initial capacity and * capacity increment. * * @param   initialCapacity the initial capacity of the vector * @param   capacityIncrement   the amount by which the capacity is * increased when the vector overflows * @throws IllegalArgumentException if the specified initial capacity * is negative * 初始化容器，并指定初始容量和扩容大小 */ public Vector(int initialCapacity, int capacityIncrement) { super(); if (initialCapacity < 0) throw new IllegalArgumentException("Illegal Capacity: "+ initialCapacity); this.elementData = new Object[initialCapacity]; this.capacityIncrement = capacityIncrement; } /** * Constructs an empty vector with the specified initial capacity and * with its capacity increment equal to zero. * * @param   initialCapacity   the initial capacity of the vector * @throws IllegalArgumentException if the specified initial capacity * is negative * 初始化容器并指定初始容量，扩容大小默认为0(即每次扩容为原来的两倍) */ public Vector(int initialCapacity) { this(initialCapacity, 0); } /** * Constructs an empty vector so that its internal data array * has size {@code 10} and its standard capacity increment is * zero. * 初始化容器并指定初始容量10，扩容大小默认为0(即每次扩容为原来的两倍) */ public Vector() { this(10); } /** * Constructs a vector containing the elements of the specified * collection, in the order they are returned by the collection's * iterator. * * @param c the collection whose elements are to be placed into this * vector * @throws NullPointerException if the specified collection is null * @since   1.2 * 以一个集合为默认元素，初始化容器 */ public Vector(Collection<? extends E> c) { elementData = c.toArray(); elementCount = elementData.length; // c.toArray might (incorrectly) not return Object[] (see 6260652) if (elementData.getClass() != Object[].class) elementData = Arrays.copyOf(elementData, elementCount, Object[].class); }

  

 

  
1
  
2
  
3
  
4
  
5
  
6
  
7
  
8
  
9
  
10
  
11
  
12
  
13
  
14
  
15
  
16
  
17
  
18
  
19
  
20
  
21
  
22
  
23
  
24
  
25
  
26
  
27
  
28
  
29
  
30
  
31
  
32
  
33
  
34
  
35
  
36
  
37
  
38
  
39
  
40
  
41
  
42
  
43
  
44
  
45
  
46
  
47
  
48
  
49
  
50
  
51
  
52
  
53
  
54
  
55
  
56
  
57
  
58
  
59
  
60
  
61
  
62
  
63
  
64
  
65
  
66
  
67
  
68
  
69
  
70
  
71
  
72
  
73
  
74
  
75
  
76
  
77
  
78
  
79
  
80
  
81
  
82
  
83
  
84
  
85
  
86
  
87
  
88
  
89
  
90
  
91
  
92
  
93
  
94
 

3：增删查改

增加和删除操作才算作结构的改变，才会记录修改次数。修改时不记录修改次数。
3.1：增加元素

   /** * Appends the specified element to the end of this Vector. * * @param e element to be appended to this Vector * @return {@code true} (as specified by {@link Collection#add}) * @since 1.2 * 插入元素到数组的末尾 */ public synchronized boolean add(E e) { modCount++; ensureCapacityHelper(elementCount + 1); elementData[elementCount++] = e; return true; } /** * Adds the specified component to the end of this vector, * increasing its size by one. The capacity of this vector is * increased if its size becomes greater than its capacity. * * <p>This method is identical in functionality to the * {@link #add(Object) add(E)} * method (which is part of the {@link List} interface). * * @param   obj   the component to be added * 与add(E e)方法相同，但是没有返回值 */ public synchronized void addElement(E obj) { modCount++; ensureCapacityHelper(elementCount + 1); elementData[elementCount++] = obj; } /** * This implements the unsynchronized semantics of ensureCapacity. * Synchronized methods in this class can internally call this * method for ensuring capacity without incurring the cost of an * extra synchronization. * * @see #ensureCapacity(int) * 超出容量即进行扩增 */ private void ensureCapacityHelper(int minCapacity) { // overflow-conscious code if (minCapacity - elementData.length > 0) grow(minCapacity); } /** * The maximum size of array to allocate. * Some VMs reserve some header words in an array. * Attempts to allocate larger arrays may result in * OutOfMemoryError: Requested array size exceeds VM limit * 允许数组最大容量值 */ private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8; // 容量扩增处理  private void grow(int minCapacity) { // overflow-conscious code int oldCapacity = elementData.length; int newCapacity = oldCapacity + ((capacityIncrement > 0) ? capacityIncrement : oldCapacity); if (newCapacity - minCapacity < 0) newCapacity = minCapacity; if (newCapacity - MAX_ARRAY_SIZE > 0) newCapacity = hugeCapacity(minCapacity); elementData = Arrays.copyOf(elementData, newCapacity); } /** * Inserts the specified element at the specified position in this Vector. * Shifts the element currently at that position (if any) and any * subsequent elements to the right (adds one to their indices). * * @param index index at which the specified element is to be inserted * @param element element to be inserted * @throws ArrayIndexOutOfBoundsException if the index is out of range * ({@code index < 0 || index > size()}) * @since 1.2 * 在某个位置插入元素 */ public void add(int index, E element) { insertElementAt(element, index); } /** * Inserts the specified object as a component in this vector at the * specified {@code index}. Each component in this vector with * an index greater or equal to the specified {@code index} is * shifted upward to have an index one greater than the value it had * previously. * * <p>The index must be a value greater than or equal to {@code 0} * and less than or equal to the current size of the vector. (If the * index is equal to the current size of the vector, the new element * is appended to the Vector.) * * <p>This method is identical in functionality to the * {@link #add(int, Object) add(int, E)} * method (which is part of the {@link List} interface).  Note that the * {@code add} method reverses the order of the parameters, to more closely * match array usage. * * @param obj the component to insert * @param index   where to insert the new component * @throws ArrayIndexOutOfBoundsException if the index is out of range * ({@code index < 0 || index > size()}) * 在某个位置插入元素 */ 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++; }

  

 

  
1
  
2
  
3
  
4
  
5
  
6
  
7
  
8
  
9
  
10
  
11
  
12
  
13
  
14
  
15
  
16
  
17
  
18
  
19
  
20
  
21
  
22
  
23
  
24
  
25
  
26
  
27
  
28
  
29
  
30
  
31
  
32
  
33
  
34
  
35
  
36
  
37
  
38
  
39
  
40
  
41
  
42
  
43
  
44
  
45
  
46
  
47
  
48
  
49
  
50
  
51
  
52
  
53
  
54
  
55
  
56
  
57
  
58
  
59
  
60
  
61
  
62
  
63
  
64
  
65
  
66
  
67
  
68
  
69
  
70
  
71
  
72
  
73
  
74
  
75
  
76
  
77
  
78
  
79
  
80
  
81
  
82
  
83
  
84
  
85
  
86
  
87
  
88
  
89
  
90
  
91
  
92
  
93
  
94
  
95
  
96
  
97
  
98
  
99
  
100
  
101
  
102
  
103
  
104
  
105
  
106
  
107
  
108
  
109
  
110
  
111
  
112
  
113
  
114
  
115
  
116
  
117
  
118
  
119
  
120
 

文章来源: javalib.blog.csdn.net，作者：陈皮的JavaLib，版权归原作者所有，如需转载，请联系作者。

原文链接：javalib.blog.csdn.net/article/details/105983916