Vector源码分析

成员变量

protected Object[] elementData;

Vector内部实现的数组

protected int elementCount;

包含的元素个数

protected int capacityIncrement;

Vector每次扩容时增加的元素个数，如果不大于0，则每次扩容时以成倍的速度增长

构造方法

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);
}

/**
* 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
*/
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);
}

构造方法同ArrayList的基本类似，不同的地方在于Vector可以指定数组每次扩容时的大小capacityIncrement，如果该值没有指定的话默认为0，那么数组在每次扩容的时候至少是当前数组大小的2倍。

方法

其基本方法以及方法的基本思想同ArrayList相似，不同的地方在于Vector中相关的方法会加上synchronized关键字。

总结

Vector整体代码的实现思想与ArrayList相同，二者的区别在于Vector是线程安全的，那么其性能相较于ArrayList来说有所下降。