1.简介
继承AbstractList，实现List接口，继承添加，修改，遍历，包含等父类方法。实现RandmoAccess接口，标记性接口，即Vector是支持快速随机访问的。实现Cloneable接口，可以被克隆。实现java.io.Serializable接口，支持序列化。
2.成员属性
//存储数据的数组
protected Object[] elementData;
//数组存储的元素数量
protected int elementCount;
//扩容时增加的容量
protected int capacityIncrement;
3.构造函数
/**
* 初始化数组长度为10
*/
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
/**
* 自增容量是0
*/
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
/**
* 数组长度为10
*/
public Vector() {
this(10);
}
/**
* 也支持从其他容器构造
*/
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);
}
4.方法分析
synchronized boolean add(E e)
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}
private void ensureCapacityHelper(int minCapacity) {
// overflow-conscious code
//当前的最小容量比实际容量大，就扩容
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//扩容oldCapacity+oldCapacity 即：扩容为原来的2倍
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);
}
//大容量扩容，最大支持到int的最大值
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
void add(int index, E element)
public void add(int index, E element) {
insertElementAt(element, index);
}
public synchronized void insertElementAt(E obj, int index) {
modCount++;
if (index > elementCount) {
throw new ArrayIndexOutOfBoundsException(index
+ " > " + elementCount);
}
//扩容
ensureCapacityHelper(elementCount + 1);
//拷贝数组
System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
elementData[index] = obj;
elementCount++;
}
synchronized E get(int index)
public synchronized E get(int index) {
//判断是否越界
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
return elementData(index);
}
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
synchronized E remove(int index)
public synchronized E remove(int index) {
modCount++;
//判断是否越界
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
E oldValue = elementData(index);
//移动数组剩余元素
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;
}
boolean remove(Object o)
public boolean remove(Object o) {
return removeElement(o);
}
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}
public int indexOf(Object o) {
return indexOf(o, 0);
}
//获取元素所在索引
public synchronized int indexOf(Object o, int index) {
if (o == null) {
for (int i = index ; i < elementCount ; i++)
if (elementData[i]==null)
return i;
} else {
for (int i = index ; i < elementCount ; i++)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
//移除指定索引的元素
public synchronized void removeElementAt(int index) {
modCount++;
//判断是否越界
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
else if (index < 0) {
throw new ArrayIndexOutOfBoundsException(index);
}
//移动数组剩余元素
int j = elementCount - index - 1;
if (j > 0) {
System.arraycopy(elementData, index + 1, elementData, index, j);
}
elementCount--;
elementData[elementCount] = null;
}
5.总结
Vector底层也是数组。存储的元素是有序的。存储元素可以重复。随机访问效率高，增删效率低。通过索引可以很快的查找到对应元素，而增删元素许多元素的位置都要改变。线程安全，通过synchronized加锁实现同步。
