概述
文章的内容基于JDK1.7进行分析，之所以选用这个版本，是因为1.8的有些类做了改动，增加了阅读的难度，虽然是1.7，但是对于1.8做了重大改动的内容，文章也会进行说明。
Vector作为List的另外一个典型实现类，完全支持List的全部功能，Vector类也封装了一个动态的，允许在分配的Object[]数组，Vector是一个比较古老的集合，JDK1.0就已经存在，建议尽量不要使用这个集合，Vector与ArrayList的主要是区别是，Vector是线程安全的，但是性能比ArrayList要低。
数据结构
继承关系
java.lang.Object
java.util.AbstractCollection<E>
java.util.AbstractList<E>
java.util.Vector<E>
实现接口
Serializable, Cloneable, Iterable<E>, Collection<E>, List<E>, RandomAccess
子类
Stack
基本属性
protected Object[] elementData; //存放元素的数组
protected int elementCount; //已经放入数组的元素个数
protected int capacityIncrement; //数组的增长系数
Vector源码解析
package java.util;
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
//定义数组，存放元素
protected Object[] elementData;
//已经放入数组的元素数量
protected int elementCount;
//增长的系数
protected int capacityIncrement;
//可序列化版本号
private static final long serialVersionUID = -2767605614048989439L;
//构造方法，提供初始大小，和增长系数
public Vector(int initialCapacity, int capacityIncrement) {
super();
if (initialCapacity < 0)
throw new IllegalArgumentException("Illegal Capacity: "+
initialCapacity);
this.elementData = new Object[initialCapacity];
this.capacityIncrement = capacityIncrement;
}
//构造方法，提供初始大小，增长系数为零
public Vector(int initialCapacity) {
this(initialCapacity, 0);
}
//无参构造方法
public Vector() {
this(10);
}
//构造方法，将指定的集合元素转化为Vector
public Vector(Collection<? extends E> c) {
elementData = c.toArray();
elementCount = elementData.length;
// c.toArray might (incorrectly) not return Object[] (see 6260652)
//判断c.toArray是否是Object[]类型
if (elementData.getClass() != Object[].class)
elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
}
//将elementData中的元素全部拷贝到anArray数组中
public synchronized void copyInto(Object[] anArray) {
System.arraycopy(elementData, 0, anArray, 0, elementCount);
}
//将数组长度设置为等于vector的个数
public synchronized void trimToSize() {
modCount++;
int oldCapacity = elementData.length;
if (elementCount < oldCapacity) {
elementData = Arrays.copyOf(elementData, elementCount);
}
}
//扩充容量
public synchronized void ensureCapacity(int minCapacity) {
if (minCapacity > 0) {
modCount++;
ensureCapacityHelper(minCapacity);
}
}
//扩充容量帮助函数
private void ensureCapacityHelper(int minCapacity) {
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
//最大容量
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//扩充容量执行方法
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//根据capacityIncrement进行判断，capacityIncrement> 0 增加capacityIncrement个容量，否则容量扩充当前容量的一倍
int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
capacityIncrement : oldCapacity);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
//扩容操作，生成已给新的数组，容量为newCapacity,并将elementData中的元素全部拷贝到新数组中，并将新生成的数组在赋值给elementData
elementData = Arrays.copyOf(elementData, newCapacity);
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
//设置size
public synchronized void setSize(int newSize) {
modCount++;
if (newSize > elementCount) {
ensureCapacityHelper(newSize);
} else {
for (int i = newSize ; i < elementCount ; i++) {
elementData[i] = null;
}
}
elementCount = newSize;
}
//返回当前容量
public synchronized int capacity() {
return elementData.length;
}
//返回vector的元素个数
public synchronized int size() {
return elementCount;
}
//是否为空
public synchronized boolean isEmpty() {
return elementCount == 0;
}
//返回vector中全部元素对应的Enumeration
public Enumeration<E> elements() {
//匿名内部类实现
return new Enumeration<E>() {
int count = 0;
public boolean hasMoreElements() {
return count < elementCount;
}
public E nextElement() {
synchronized (Vector.this) {
if (count < elementCount) {
return elementData(count++);
}
}
throw new NoSuchElementException("Vector Enumeration");
}
};
}
//是否包含Object对线o
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
}
//返回 o 对象的位置
public int indexOf(Object o) {
return indexOf(o, 0);
}
//从index位置开始，向后查找Object对象 （o）
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;
}
//倒序查找对象 o
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
}
//从最后一个元素开始，向前查找对象o ,找到返回元素的索引，否则返回 -1
public synchronized int lastIndexOf(Object o, int index) {
if (index >= elementCount)
throw new IndexOutOfBoundsException(index + " >= "+ elementCount);
if (o == null) {
for (int i = index; i >= 0; i--)
if (elementData[i]==null)
return i;
} else {
for (int i = index; i >= 0; i--)
if (o.equals(elementData[i]))
return i;
}
return -1;
}
//返回索引为index的元素
public synchronized E elementAt(int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
}
return elementData(index);
}
//返回第一个元素
public synchronized E firstElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(0);
}
//返回最后一个元素
public synchronized E lastElement() {
if (elementCount == 0) {
throw new NoSuchElementException();
}
return elementData(elementCount - 1);
}
//将index位置的元素设置为obj
public synchronized void setElementAt(E obj, int index) {
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
elementData[index] = obj;
}
//删除指定位置的元素，Object[]对象数组从index+1开始向前依次移动一个位置
public synchronized void removeElementAt(int index) {
modCount++;
if (index >= elementCount) {
throw new ArrayIndexOutOfBoundsException(index + " >= " +
elementCount);
}
else if (index < 0) {
throw new ArrayIndexOutOfBoundsException(index);
}
int j = elementCount - index - 1;
if (j > 0) {
System.arraycopy(elementData, index + 1, elementData, index, j);
}
elementCount--;
elementData[elementCount] = null; /* to let gc do its work */
}
//将obj元素插入index位置
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++;
}
//添加元素
public synchronized void addElement(E obj) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = obj;
}
//删除元素 ，删除成功返回true, 否则返回false
public synchronized boolean removeElement(Object obj) {
modCount++;
int i = indexOf(obj);
if (i >= 0) {
removeElementAt(i);
return true;
}
return false;
}
//清空所有的元素
public synchronized void removeAllElements() {
modCount++;
// Let gc do its work
for (int i = 0; i < elementCount; i++)
elementData[i] = null;
elementCount = 0;
}
//克隆方法
public synchronized Object clone() {
try {
@SuppressWarnings("unchecked")
Vector<E> v = (Vector<E>) super.clone();
v.elementData = Arrays.copyOf(elementData, elementCount);
v.modCount = 0;
return v;
} catch (CloneNotSupportedException e) {
// this shouldn't happen, since we are Cloneable
throw new InternalError();
}
}
//转化为数组
public synchronized Object[] toArray() {
return Arrays.copyOf(elementData, elementCount);
}
//转化为指定类型的数组
@SuppressWarnings("unchecked")
public synchronized <T> T[] toArray(T[] a) {
if (a.length < elementCount)
return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());
System.arraycopy(elementData, 0, a, 0, elementCount);
if (a.length > elementCount)
a[elementCount] = null;
return a;
}
// Positional Access Operations
@SuppressWarnings("unchecked")
E elementData(int index) {
return (E) elementData[index];
}
//得到索引为index的元素
public synchronized E get(int index) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
return elementData(index);
}
//设置index位置的元素为element
public synchronized E set(int index, E element) {
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
E oldValue = elementData(index);
elementData[index] = element;
return oldValue;
}
//添加方法
public synchronized boolean add(E e) {
modCount++;
ensureCapacityHelper(elementCount + 1);
elementData[elementCount++] = e;
return true;
}
//删除操作
public boolean remove(Object o) {
return removeElement(o);
}
//将element添加到index位置上
public void add(int index, E element) {
insertElementAt(element, index);
}
//删除index位置的元素
public synchronized E remove(int index) {
modCount++;
if (index >= elementCount)
throw new ArrayIndexOutOfBoundsException(index);
E oldValue = elementData(index);
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;
}
//清除
public void clear() {
removeAllElements();
}
// Bulk Operations
//是否包含集合c中所有的元素
public synchronized boolean containsAll(Collection<?> c) {
return super.containsAll(c);
}
//将集合c中所有的元素添加到列表中，借助System.copyOf()方法实现
public synchronized boolean addAll(Collection<? extends E> c) {
modCount++;
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityHelper(elementCount + numNew);
System.arraycopy(a, 0, elementData, elementCount, numNew);
elementCount += numNew;
return numNew != 0;
}
//删除集合c中所有的元素
public synchronized boolean removeAll(Collection<?> c) {
return super.removeAll(c);
}
public synchronized boolean retainAll(Collection<?> c) {
return super.retainAll(c);
}
//将集合c 添加到index之后的位置上
public synchronized boolean addAll(int index, Collection<? extends E> c) {
modCount++;
if (index < 0 || index > elementCount)
throw new ArrayIndexOutOfBoundsException(index);
Object[] a = c.toArray();
int numNew = a.length;
ensureCapacityHelper(elementCount + numNew);
int numMoved = elementCount - index;
if (numMoved > 0)
System.arraycopy(elementData, index, elementData, index + numNew,
numMoved);
System.arraycopy(a, 0, elementData, index, numNew);
elementCount += numNew;
return numNew != 0;
}
//判断方法
public synchronized boolean equals(Object o) {
return super.equals(o);
}
//计算hashCode值
public synchronized int hashCode() {
return super.hashCode();
}
public synchronized String toString() {
return super.toString();
}
//返回从fromIndex到toIndex之间的子集合
public synchronized List<E> subList(int fromIndex, int toIndex) {
return Collections.synchronizedList(super.subList(fromIndex, toIndex),
this);
}
//范围删除元素
protected synchronized void removeRange(int fromIndex, int toIndex) {
modCount++;
int numMoved = elementCount - toIndex;
System.arraycopy(elementData, toIndex, elementData, fromIndex,
numMoved);
// Let gc do its work
int newElementCount = elementCount - (toIndex-fromIndex);
while (elementCount != newElementCount)
elementData[--elementCount] = null;
}
//将对象写入到输出流中
private void writeObject(java.io.ObjectOutputStream s)
throws java.io.IOException {
final java.io.ObjectOutputStream.PutField fields = s.putFields();
final Object[] data;
synchronized (this) {
fields.put("capacityIncrement", capacityIncrement);
fields.put("elementCount", elementCount);
data = elementData.clone();
}
fields.put("elementData", data);
s.writeFields();
}
public synchronized ListIterator<E> listIterator(int index) {
if (index < 0 || index > elementCount)
throw new IndexOutOfBoundsException("Index: "+index);
return new ListItr(index);
}
public synchronized ListIterator<E> listIterator() {
return new ListItr(0);
}
public synchronized Iterator<E> iterator() {
return new Itr();
}
//省略了内部类的实现
}
总结
Vector和ArrayList的实现方式可以看出非常的想象，既然Vector类建议尽量少的使用，还是最好不要用了，通过上面的源码发现，每个方法中都添加了synchronized的关键字来保证同步，所以它是线程安全的，但正是这些方法的同步，让它的效率大大的降低了，比ArrayList的效率要慢。
少年听雨歌楼上，红烛昏罗帐。
壮年听雨客舟中，江阔云低，断雁叫西风。
感谢支持！
---起个名忒难
