Vector 详细介绍(源码分析)

主要以下层面去分析Vector

Vector介绍

Vector架构设计(数据结构)

Vector源码分析

Vector遍历方式,性能,示例

Vector介绍

Vector简介

Vector 是矢量队列,它是JDK1.0版本添加的类。继承于AbstractList,实现了List, RandomAccess, Cloneable这些接口。
Vector 继承了AbstractList,实现了List;所以,它是一个队列,支持相关的添加、删除、修改、遍历等功能
Vector 实现了RandmoAccess接口,即提供了随机访问功能。RandmoAccess是java中用来被List实现,为List提供快速访问功能的。在Vector中,我们即可以通过元素的序号快速获取元素对象;这就是快速随机访问。
Vector 实现了Cloneable接口,即实现clone()函数。它能被克隆。

和ArrayList不同,Vector中的操作是线程安全的

Vector类的4个构造函数:

// capacity是Vector的默认容量大小,capacityIncrement是每次Vector容量增加时的增量值。  
 public Vector(int initialCapacity, int capacityIncrement) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        //新建一个数组,数组容量是initialCapacity
        this.elementData = new Object[initialCapacity];
        //设置增长容量增长系数
        this.capacityIncrement = capacityIncrement;
    }

  //设置初始化容量,当由于增加数据导致容量增加时,每次容量会增加一倍。
    public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }

 //默认构造函数 ,未指定,默认初始化容量是10
    public Vector() {
        this(10);
    }

   
    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);
    }

Vector 的API

 

synchronized boolean        add(E object)
             void           add(int location, E object)
synchronized boolean        addAll(Collection<? extends E> collection)
synchronized boolean        addAll(int location, Collection<? extends E> collection)
synchronized void           addElement(E object)
synchronized int            capacity()
             void           clear()
synchronized Object         clone()
             boolean        contains(Object object)
synchronized boolean        containsAll(Collection<?> collection)
synchronized void           copyInto(Object[] elements)
synchronized E              elementAt(int location)
             Enumeration<E> elements()
synchronized void           ensureCapacity(int minimumCapacity)
synchronized boolean        equals(Object object)
synchronized E              firstElement()
             E              get(int location)
synchronized int            hashCode()
synchronized int            indexOf(Object object, int location)
             int            indexOf(Object object)
synchronized void           insertElementAt(E object, int location)
synchronized boolean        isEmpty()
synchronized E              lastElement()
synchronized int            lastIndexOf(Object object, int location)
synchronized int            lastIndexOf(Object object)
synchronized E              remove(int location)
             boolean        remove(Object object)
synchronized boolean        removeAll(Collection<?> collection)
synchronized void           removeAllElements()
synchronized boolean        removeElement(Object object)
synchronized void           removeElementAt(int location)
synchronized boolean        retainAll(Collection<?> collection)
synchronized E              set(int location, E object)
synchronized void           setElementAt(E object, int location)
synchronized void           setSize(int length)
synchronized int            size()
synchronized List<E>        subList(int start, int end)
synchronized <T> T[]        toArray(T[] contents)
synchronized Object[]       toArray()
synchronized String         toString()
synchronized void           trimToSize()

看到每个方法都添加了synchronized。 

Vector架构设计(数据结构)

Vector的继承关系如下所示:

java.lang.Object
   ↳     java.util.AbstractCollection<E>
         ↳     java.util.AbstractList<E>
               ↳     java.util.Vector<E>

public class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable

Vector与Collection关系如下图

Vector的数据结构和ArrayList差不多,它包含了3个成员变量:elementData , elementCount, capacityIncrement。

(1) elementData 是"Object[]类型的数组",它保存了添加到Vector中的元素。elementData是个动态数组,如果初始化Vector时,没指定动态数组的>大小,则使用默认大小10。随着Vector中元素的增加,Vector的容量也会动态增长,capacityIncrement是与容量增长相关的增长系数,具体的增长方式,请参考源码分析中的ensureCapacity()函数。

(2) elementCount 是动态数组的实际大小。

(3) capacityIncrement 是动态数组的增长系数。如果在创建Vector时,指定了capacityIncrement的大小;则,每次当Vector中动态数组容量增加时>,增加的大小都是capacityIncrement。

Vector源码分析

public class Vector<E>
        extends AbstractList<E>
        implements List<E>, RandomAccess, Cloneable, java.io.Serializable {
    /**
     * 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
     */
    //保存Vector中数据的数组
    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
     */
    //数组实际的长度
    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
     */
    //扩容因子(容量增长系数)
    protected int capacityIncrement;

    /**
     * use serialVersionUID from JDK 1.0.2 for interoperability
     */
    //vector的序列化版本号
    private static final long serialVersionUID = -2767605614048989439L;

    /**
     * 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
     */
    // 指定Vector"容量大小"和"增长系数"的构造函数
    public Vector(int initialCapacity, int capacityIncrement) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: " +
                    initialCapacity);
        //新建一个数组,数组容量是initialCapacity
        this.elementData = new Object[initialCapacity];
        //设置增长容量增长系数
        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
     */
    //指定初始化容量的构造函数
    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.
     */
    //无参构造,初始化容量设置为10
    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
     */
    //指定几个的Vector的构造函数
    public Vector(Collection<? extends E> c) {
        //获取集合C的数组,并将其值赋值给elementData
        elementData = c.toArray();
        //设置数组长度
        elementCount = elementData.length;
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        //把
        if (elementData.getClass() != Object[].class)
            //Arrays.copyOf()不仅仅只是拷贝数组中的元素,在拷贝元素时,会创建一个新的数组对象。
            elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
    }

    /**
     * Copies the components of this vector into the specified array.
     * The item at index {@code k} in this vector is copied into
     * component {@code k} of {@code anArray}.
     *
     * @param anArray the array into which the components get copied
     * @throws NullPointerException      if the given array is null
     * @throws IndexOutOfBoundsException if the specified array is not
     *                                   large enough to hold all the components of this vector
     * @throws ArrayStoreException       if a component of this vector is not of
     *                                   a runtime type that can be stored in the specified array
     * @see #toArray(Object[])
     */
    //将数组Vector的全部元素都拷贝到数组anArray中
    public synchronized void copyInto(Object[] anArray) {
        System.arraycopy(elementData, 0, anArray, 0, elementCount);
    }

    /**
     * Trims the capacity of this vector to be the vector's current
     * size. If the capacity of this vector is larger than its current
     * size, then the capacity is changed to equal the size by replacing
     * its internal data array, kept in the field {@code elementData},
     * with a smaller one. An application can use this operation to
     * minimize the storage of a vector.
     */
    //将当前容量值设置为等于实际元素个数
    public synchronized void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (elementCount < oldCapacity) {
            elementData = Arrays.copyOf(elementData, elementCount);
        }
    }

    /**
     * Increases the capacity of this vector, if necessary, to ensure
     * that it can hold at least the number of components specified by
     * the minimum capacity argument.
     *
     * <p>If the current capacity of this vector is less than
     * {@code minCapacity}, then its capacity is increased by replacing its
     * internal data array, kept in the field {@code elementData}, with a
     * larger one.  The size of the new data array will be the old size plus
     * {@code capacityIncrement}, unless the value of
     * {@code capacityIncrement} is less than or equal to zero, in which case
     * the new capacity will be twice the old capacity; but if this new size
     * is still smaller than {@code minCapacity}, then the new capacity will
     * be {@code minCapacity}.
     *
     * @param minCapacity the desired minimum capacity
     */
    //确认Vecotr容量的辅助函数,在执行扩容的时候使用到
    public synchronized void ensureCapacity(int minCapacity) {
        if (minCapacity > 0) {
            //每次数据结构改变,这里的modcount都会变化,这里我的理解是主要为了jdk的fail-fast机制使用
            modCount++;
            //这里主要是执行的grow(),也就是扩容操作,  当Vector的容量不足以容纳当前的全部元素,增加容量大小。
            ensureCapacityHelper(minCapacity);
         /*   //获取当前数组的长度
            int oldCapacity = elementData.length;

            // 若 容量增量系数>0(即capacityIncrement>0),则将容量增大当capacityIncrement。
            // 否则,将容量增大一倍。
            int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
                    capacityIncrement : oldCapacity);
            if (newCapacity - minCapacity < 0)
                newCapacity = minCapacity;
            if (newCapacity - MAX_ARRAY_SIZE > 0)
                //巨大扩容函数
                newCapacity = hugeCapacity(minCapacity);
            //扩容后要进行执行copy操作
            elementData = Arrays.copyOf(elementData, newCapacity);*/
        }
    }

    /**
     * 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)
     */

    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
     */
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    //真正的扩容函数。
    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);
    }

    //巨大扩容函数
    private static int hugeCapacity(int minCapacity) {
        if (minCapacity < 0) // overflow
            throw new OutOfMemoryError();
        return (minCapacity > MAX_ARRAY_SIZE) ?
                Integer.MAX_VALUE :
                MAX_ARRAY_SIZE;
    }

    /**
     * Sets the size of this vector. If the new size is greater than the
     * current size, new {@code null} items are added to the end of
     * the vector. If the new size is less than the current size, all
     * components at index {@code newSize} and greater are discarded.
     *
     * @param newSize the new size of this vector
     * @throws ArrayIndexOutOfBoundsException if the new size is negative
     */
    //设置容量值,看代码其实很简单,就是几个获取和赋值而已
    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;
    }

    /**
     * Returns the current capacity of this vector.
     *
     * @return the current capacity (the length of its internal
     * data array, kept in the field {@code elementData}
     * of this vector)
     */
    //返回Vector总的容量
    public synchronized int capacity() {
        return elementData.length;
    }

    /**
     * Returns the number of components in this vector.
     *
     * @return the number of components in this vector
     */
    //返回Vector的实际大小
    public synchronized int size() {
        return elementCount;
    }

    /**
     * Tests if this vector has no components.
     *
     * @return {@code true} if and only if this vector has
     * no components, that is, its size is zero;
     * {@code false} otherwise.
     */
    //判断是否为null
    public synchronized boolean isEmpty() {
        return elementCount == 0;
    }

    /**
     * Returns an enumeration of the components of this vector. The
     * returned {@code Enumeration} object will generate all items in
     * this vector. The first item generated is the item at index {@code 0},
     * then the item at index {@code 1}, and so on.
     *
     * @return an enumeration of the components of this vector
     * @see Iterator
     */
    //返回“Vector中全部元素对应的Enumeration”
    public Enumeration<E> elements() {
        // 通过匿名类实现Enumeration
        return new Enumeration<E>() {
            int count = 0;
            // 是否存在下一个元素
            public boolean hasMoreElements() {
                return count < elementCount;
            }
            // 获取下一个元素
            public E nextElement() {
                synchronized (Vector.this) {
                    if (count < elementCount) {
                        return elementData(count++);
                    }
                }
                throw new NoSuchElementException("Vector Enumeration");
            }
        };
    }

    /**
     * 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&nbsp;?&nbsp;e==null&nbsp;:&nbsp;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
     */
    // 返回Vector中是否包含对象(o)
    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&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;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
     */

    // 查找并返回元素(o)在Vector中的索引值
    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&nbsp;&gt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;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 {
                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&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;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
     */
    // 从后向前查找元素(o)。并返回元素的索引
    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&nbsp;&lt;=&nbsp;index&nbsp;&amp;&amp;&nbsp;(o==null&nbsp;?&nbsp;get(i)==null&nbsp;:&nbsp;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
     */
    // 从后向前查找元素(o)。开始位置是从前向后的第index个数;
    // 若找到,则返回元素的“索引值”;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;
    }

    /**
     * Returns the component at the specified index.
     *
     * <p>This method is identical in functionality to the {@link #get(int)}
     * method (which is part of the {@link List} interface).
     *
     * @param index an index into this vector
     * @return the component at the specified index
     * @throws ArrayIndexOutOfBoundsException if the index is out of range
     *                                        ({@code index < 0 || index >= size()})
     */
    // 返回Vector中index位置的元素。
   // 若index月结,则抛出异常
    public synchronized E elementAt(int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
        }

        return elementData(index);
    }

    /**
     * Returns the first component (the item at index {@code 0}) of
     * this vector.
     *
     * @return the first component of this vector
     * @throws NoSuchElementException if this vector has no components
     */
    // 获取Vector中的第一个元素。
     // 若失败,则抛出异常!
    public synchronized E firstElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(0);
    }

    /**
     * Returns the last component of the vector.
     *
     * @return the last component of the vector, i.e., the component at index
     * <code>size()&nbsp;-&nbsp;1</code>.
     * @throws NoSuchElementException if this vector is empty
     */
    public synchronized E lastElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(elementCount - 1);
    }
  // 设置index位置的元素值为obj
    public synchronized void setElementAt(E obj, int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " +
                                 elementCount);
        }
        elementData[index] = obj;
    }

    // 删除index位置的元素
    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 */
    }

    // 在index位置处插入元素(obj)
    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++;
    }

    // 将“元素obj”添加到Vector末尾
    public synchronized void addElement(E obj) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = obj;
    }

    // 在Vector中查找并删除元素obj。
    // 成功的话,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;
    }

    // 删除Vector中的全部元素
    public synchronized void removeAllElements() {
        modCount++;
        // 将Vector中的全部元素设为null
        for (int i = 0; i < elementCount; i++)
            elementData[i] = null;

        elementCount = 0;
    }

    // 克隆函数
    public synchronized Object clone() {
        try {
            Vector<E> v = (Vector<E>) super.clone();
            // 将当前Vector的全部元素拷贝到v中
            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();
        }
    }

    // 返回Object数组
    public synchronized Object[] toArray() {
        return Arrays.copyOf(elementData, elementCount);
    }

    // 返回Vector的模板数组。所谓模板数组,即可以将T设为任意的数据类型
    public synchronized <T> T[] toArray(T[] a) {
        // 若数组a的大小 < Vector的元素个数;
        // 则新建一个T[]数组,数组大小是“Vector的元素个数”,并将“Vector”全部拷贝到新数组中
        if (a.length < elementCount)
            return (T[]) Arrays.copyOf(elementData, elementCount, a.getClass());

        // 若数组a的大小 >= Vector的元素个数;
        // 则将Vector的全部元素都拷贝到数组a中。
    System.arraycopy(elementData, 0, a, 0, elementCount);

        if (a.length > elementCount)
            a[elementCount] = null;

        return a;
    }

    // 获取index位置的元素
    public synchronized E get(int index) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        return (E)elementData[index];
    }

    // 设置index位置的值为element。并返回index位置的原始值
    public synchronized E set(int index, E element) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        Object oldValue = elementData[index];
        elementData[index] = element;
        return (E)oldValue;
    }

    // 将“元素e”添加到Vector最后。
    public synchronized boolean add(E e) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

    // 删除Vector中的元素o
    public boolean remove(Object o) {
        return removeElement(o);
    }

    // 在index位置添加元素element
    public void add(int index, E element) {
        insertElementAt(element, index);
    }

    // 删除index位置的元素,并返回index位置的原始值
    public synchronized E remove(int index) {
        modCount++;
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);
        Object 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 (E)oldValue;
    }

    // 清空Vector
    public void clear() {
        removeAllElements();
    }

    // 返回Vector是否包含集合c
    public synchronized boolean containsAll(Collection<?> c) {
        return super.containsAll(c);
    }

    // 将集合c添加到Vector中
    public synchronized boolean addAll(Collection<? extends E> c) {
        modCount++;
        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacityHelper(elementCount + numNew);
        // 将集合c的全部元素拷贝到数组elementData中
        System.arraycopy(a, 0, elementData, elementCount, numNew);
        elementCount += numNew;
        return numNew != 0;
    }

    // 删除集合c的全部元素
    public synchronized boolean removeAll(Collection<?> c) {
        return super.removeAll(c);
    }

    // 删除“非集合c中的元素”
    public synchronized boolean retainAll(Collection<?> c)  {
        return super.retainAll(c);
    }

    // 从index位置开始,将集合c添加到Vector中
    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;
    }

    // 返回两个对象是否相等
    public synchronized boolean equals(Object o) {
        return super.equals(o);
    }

    // 计算哈希值
    public synchronized int hashCode() {
        return super.hashCode();
    }

    // 调用父类的toString()
    public synchronized String toString() {
        return super.toString();
    }

    // 获取Vector中fromIndex(包括)到toIndex(不包括)的子集
    public synchronized List<E> subList(int fromIndex, int toIndex) {
        return Collections.synchronizedList(super.subList(fromIndex, toIndex), this);
    }

    // 删除Vector中fromIndex到toIndex的元素
    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;
    }

    // java.io.Serializable的写入函数
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws java.io.IOException {
        s.defaultWriteObject();
    }
}

总结
(1) Vector实际上是通过一个数组去保存数据的。当我们构造Vector时;若使用默认构造函数,则Vector的默认容量大小是10
(2) 当Vector容量不足以容纳全部元素时,Vector的容量会增加。若容量增加系数 >0,则将容量的值增加“容量增加系数”;否则,将容量大小增加一倍,从上面源码中可以看到扩操作执行的是frow()函数,很易懂。
(3) Vector的克隆函数,即是将全部元素克隆到一个数组中。

Vector遍历方式,遍历性能,示例

四种遍历方式: 

   Vector<Integer> vector = new Vector();

        for (int i = 0; i < 10000000; i++) {
            vector.add(i);
        }
//第一种,随机访问
        long start = System.currentTimeMillis();
        int size = vector.size();
        for (int i = 0; i < size; i++) {
            vector.get(i);
        }
        long end = System.currentTimeMillis();
        System.out.println("---------------------" + (end - start) + "---------------------");
//迭代器的遍历方式

        long start1 = System.currentTimeMillis();
        Iterator iterator = vector.iterator();
        while (iterator.hasNext()) {
            iterator.next();

        }
        long end1 = System.currentTimeMillis();
        System.out.println("-----------" + (end1 - start1) + "--------------------");

//增强for
        long start2 = System.currentTimeMillis();
        for (Integer integer : vector) {

        }
        long end2 = System.currentTimeMillis();
        System.out.println("-----------" + (end2 - start2) + "--------------------");

//Enumeration遍历
        long start3 = System.currentTimeMillis();
        Enumeration enumeration = vector.elements();
        while (enumeration.hasMoreElements()) {
            enumeration.nextElement();
        }
        long end3 = System.currentTimeMillis();
        System.out.println("-----------" + (end3 - start3) + "--------------------");

    }

下图是1000万条数据:测试结果,可以根据不同的数量来进行测试性能。


总结:达到千万级的时候:Enumeration遍历是最慢的,其他三者倒是差不多,和Arraylist性能还是有些区别的,查看Arraylist可以进行查看这篇文章,点击一下,也包含了源码分析和数据结构,可以从中领悟设计者的思想,通过什么设计模式而实现的。