Vector是List接口的另一实现，有非常长的历史了，从jdk1.0开始就有Vector了，先于ArrayList出现，与ArrayList的最大区别是：Vector 是线程安全的，简单浏览一下Vector:
类定义：
public class Vector<E>
extends AbstractList<E>
implements List<E>, RandomAccess, Cloneable, java.io.Serializable
Vector支持快速随机访问，和arrayList一样。
Vector 初始容量为10，支持自定义每次扩容长度，如果不自定义扩容长度，那么默认扩容后的长度是原来的2倍。
/**
* 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
*/
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
*/
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.
*/
public Vector() {
this(10);
}
Vector最大的特点是Vector内部基本上都使用了synchronized进行同步或者调用使用了 synchronized同步关键字的方法：
/**
* Returns {@code true} if this vector contains the specified element.
* More formally, returns {@code true} if and only if this vector
* contains at least one element {@code e} such that
* <tt>(o==null ? e==null : o.equals(e))</tt>.
*
* @param o element whose presence in this vector is to be tested
* @return {@code true} if this vector contains the specified element
*/
public boolean contains(Object o) {
return indexOf(o, 0) >= 0;
} /**
* Returns the index of the first occurrence of the specified element
* in this vector, or -1 if this vector does not contain the element.
* More formally, returns the lowest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the first occurrence of the specified element in
* this vector, or -1 if this vector does not contain the element
*/
public int indexOf(Object o) {
return indexOf(o, 0);
} /**
* Returns the index of the first occurrence of the specified element in
* this vector, searching forwards from {@code index}, or returns -1 if
* the element is not found.
* More formally, returns the lowest index {@code i} such that
* <tt>(i >= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @param index index to start searching from
* @return the index of the first occurrence of the element in
* this vector at position {@code index} or later in the vector;
* {@code -1} if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is negative
* @see Object#equals(Object)
*/
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;
} /**
* Returns the index of the last occurrence of the specified element
* in this vector, or -1 if this vector does not contain the element.
* More formally, returns the highest index {@code i} such that
* <tt>(o==null ? get(i)==null : o.equals(get(i)))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @return the index of the last occurrence of the specified element in
* this vector, or -1 if this vector does not contain the element
*/
public synchronized int lastIndexOf(Object o) {
return lastIndexOf(o, elementCount-1);
} /**
* Returns the index of the last occurrence of the specified element in
* this vector, searching backwards from {@code index}, or returns -1 if
* the element is not found.
* More formally, returns the highest index {@code i} such that
* <tt>(i <= index && (o==null ? get(i)==null : o.equals(get(i))))</tt>,
* or -1 if there is no such index.
*
* @param o element to search for
* @param index index to start searching backwards from
* @return the index of the last occurrence of the element at position
* less than or equal to {@code index} in this vector;
* -1 if the element is not found.
* @throws IndexOutOfBoundsException if the specified index is greater
* than or equal to the current size of this vector
*/
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;
}
Vector 的实现实际上跟ArrayList差别不大，ArrayList可参考 java1.7集合源码阅读：ArrayList 。