Vector特點：
1.內部通過陣列實現
2.通過synchronized同步方法，執行緒安全，適合多執行緒
3.由於執行緒安全，效率不高
4.預設存放10個元素
5.需要增加容量時候，預設新增加容量是元素Vector的大小
6.效率低，不推薦用
所在包

package java.util;

繼承AbstractList
實現List 、RandomAccess、Cloneable、java.io.Serializable
Clone：
簡單的說就是clone一個物件例項。使得clone出來的copy和原有的物件一模一樣
Serializable：
序列化

public
 
 class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable{
// 內部程式碼下面講解
}

內部通過Object陣列存放元素

protected Object[] elementData;

當前元素id

protected int elementCount;

每次可增加容量大小

protected int capacityIncrement;

use serialVersionUID from JDK 1.0.2 for interoperability

private static final long serialVersionUID = -2767605614048989439L;

構造器
initialCapacity:預設大小
capacityIncrement：可增加容量大小

 /** @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;
    }

構造器

 /* @throws IllegalArgumentException if the specified initial capacity
     *         is negative
     */
    public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }

構造器
預設只能存放10個元素

public Vector() {
        this(10);
    }

構造器
利用集合c構建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);
    }

下面方法都加了synchronized，保證執行緒安全
elementData內元素複製到anArray中

 /* @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[])
     */
    public synchronized void copyInto(Object[] anArray) {
        System.arraycopy(elementData, 0, anArray, 0, elementCount);
    }

修剪elementData，保證其內部的元素都是有效元素
elementCount 記錄實際元素個數

public synchronized void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (elementCount < oldCapacity) {
            elementData = Arrays.copyOf(elementData, elementCount);
        }
    }

增加容量

public synchronized void ensureCapacity(int minCapacity) {
        if (minCapacity > 0) {
            modCount++;
            ensureCapacityHelper(minCapacity);//是否需要增加容量
        }
    }

根據Vector長度和判斷是否需要增加容量

private void ensureCapacityHelper(int minCapacity) {
        // overflow-conscious code
        if (minCapacity - elementData.length > 0)// true 增加容量
            grow(minCapacity);
    }

能夠分配元素數量的最大值

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

擴充容量具體程式

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);
    }

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

可以看出：當不指定擴充容量的最小值時候，每次新增加的容量大小等於原始Vector的大小

設定大小，根據程式，使得newSize以後的元素清楚，只保留newsize個元素。當不足newsize個元素的時候，需要進行擴充

 /* @throws ArrayIndexOutOfBoundsException if the new size is negative
     */
    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;
    }

獲取當前Vector的容量

public synchronized int capacity() {
        return elementData.length;
    }

獲取當前Vector元素的個數

public synchronized int size() {
        return elementCount;
    }

注意兩個的區別：
容量可能比較大，個數指的是具體元素的個數
容量只能夠存放元素個數的最大值

判斷是否為空

public synchronized boolean isEmpty() {
        return elementCount == 0;
    }

獲取一個Enumeration型別的元件，可以順序的訪問Vector元素，這個和迭代器很類似

public Enumeration<E> elements() {
        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");
            }
        };
    }

判斷是否包含元素 o

public boolean contains(Object o) {
        return indexOf(o, 0) >= 0;
    }

返回元素 o 第一次出現的下標

public int indexOf(Object o) {
        return indexOf(o, 0);
    }

從index開始，查詢元素o出現的下標
當不出現的時候返回-1
實現很簡單順序查詢，比較是否相等

 /* @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;
    }

返回元素o最有一次出現的下標

public synchronized int lastIndexOf(Object o) {
        return lastIndexOf(o, elementCount-1);
    }

截止到index，返回元素o 最後一次出現的下標
不出現，返回-1

/* @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;
    }

返回index位置元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     */
    public synchronized E elementAt(int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
        }

        return elementData(index);
    }

獲取第一個元素的值

 /* @throws NoSuchElementException if this vector has no components
     */
    public synchronized E firstElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(0);
    }

獲取最後一個元素的值

 /* @throws NoSuchElementException if this vector is empty
     */
    public synchronized E lastElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(elementCount - 1);
    }

更新index位置元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     */
    public synchronized void setElementAt(E obj, int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " +
                                                     elementCount);
        }
        elementData[index] = obj;
    }

刪除index位置的元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     */
    public synchronized void removeElementAt(int index) {
        modCount++;
        if (index >= elementCount) { // 越界
            throw new ArrayIndexOutOfBoundsException(index + " >= " +
                                                     elementCount);
        }
        else if (index < 0) { // 越界
            throw new ArrayIndexOutOfBoundsException(index);
        }
        int j = elementCount - index - 1; // 需要移動元素個數
        if (j > 0) { // elementData陣列，從index+1開始複製j個元素，到該陣列的index開始位置
            System.arraycopy(elementData, index + 1, elementData, index, j);
        }
        elementCount--; // 元素個數-1 
        elementData[elementCount] = null; // 空，有利於垃圾回收
    }

index位置插入元素 o

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index > size()})
     */
    public synchronized void insertElementAt(E obj, int index) {
        modCount++;
        if (index > elementCount) { // 越界
            throw new ArrayIndexOutOfBoundsException(index
                                                     + " > " + elementCount);
        }
        ensureCapacityHelper(elementCount + 1); // 確保可以插入元素
        // index - elementCount 之間的元素 後移一位
        System.arraycopy(elementData, index, elementData, index + 1, elementCount - index);
        elementData[index] = obj; // 插入元素
        elementCount++; // 元素個數 + 1 
    }

尾部插入元素

public synchronized void addElement(E obj) {
        modCount++;
        ensureCapacityHelper(elementCount + 1); // 確保可以插入元素，當到達最大容量，進行擴容
        elementData[elementCount++] = obj;
    }

刪除元素obj

public synchronized boolean removeElement(Object obj) {
        modCount++;
        int i = indexOf(obj);
        if (i >= 0) {
            removeElementAt(i);
            return true;
        }
        return false;
    }

刪除所有元素

public synchronized void removeAllElements() {
        modCount++;
        // Let gc do its work
        for (int i = 0; i < elementCount; i++)
            elementData[i] = null;

        elementCount = 0;
    }

clone一個Vector

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();
        }
    }

Vector元素複製到陣列

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

Vector中元素複製到指定陣列

 /* @throws ArrayStoreException if the runtime type of a is not a supertype
     * of the runtime type of every element in this Vector
     * @throws NullPointerException if the given array is null
     * @since 1.2
     */
    @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;
    }

獲取index位置元素

@SuppressWarnings("unchecked")
    E elementData(int index) {
        return (E) elementData[index];
    }

獲取index位置元素，可以丟擲異常

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *            ({@code index < 0 || index >= size()})
     * @since 1.2
     */
    public synchronized E get(int index) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        return elementData(index);
    }

更新index位置元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     * @since 1.2
     */
    public synchronized E set(int index, E element) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

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

尾部新增元素

public synchronized boolean add(E e) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

刪除元素

public boolean remove(Object o) {
        return removeElement(o);
    }

index位置插入元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index > size()})
     * @since 1.2
     */
    public void add(int index, E element) {
        insertElementAt(element, index);
    }

刪除index位置元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index >= size()})
     * @param index the index of the element to be removed
     * @return element that was removed
     * @since 1.2
     */
    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;
    }

清空

public void clear() {
        removeAllElements();
    }

Vector內是否包含集合c的元素

 /* @throws NullPointerException if the specified collection is null
     */
    public synchronized boolean containsAll(Collection<?> c) {
        return super.containsAll(c);
    }

集合c中元素新增到Vector中

 /* @throws NullPointerException if the specified collection is null
     * @since 1.2
     */
    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;
    }

Vector集合 與集合c的差集

/ * @throws NullPointerException if this vector contains one or more null
     *         elements and the specified collection does not support null
     *         elements
     *         or if the specified collection is null
     * @since 1.2
     */
    public synchronized boolean removeAll(Collection<?> c) {
        return super.removeAll(c);
    }

交集

 /* @throws NullPointerException if this vector contains one or more null
     *         elements and the specified collection does not support null
     *         elements
     *         or if the specified collection is null
     * @since 1.2
     */
    public synchronized boolean retainAll(Collection<?> c) {
        return super.retainAll(c);
    }

index位置插入集合c的元素

 /* @throws ArrayIndexOutOfBoundsException if the index is out of range
     *         ({@code index < 0 || index > size()})
     * @throws NullPointerException if the specified collection is null
     * @since 1.2
     */
    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);// 是否需要增加容量

        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;
    }

重寫equals方法

public synchronized boolean equals(Object o) {
        return super.equals(o);
    }

hashcode方法

 public synchronized int hashCode() {
        return super.hashCode();
    }

轉化為字串

public synchronized String toString() {
        return super.toString();
    }

返回區間內的元素，並儲存在List中

 /* @throws IndexOutOfBoundsException if an endpoint index value is out of range
     *         {@code (fromIndex < 0 || toIndex > size)}
     * @throws IllegalArgumentException if the endpoint indices are out of order
     *         {@code (fromIndex > toIndex)}
     */
    public synchronized List<E> subList(int fromIndex, int toIndex) {
        return Collections.synchronizedList(super.subList(fromIndex, toIndex),
                                            this);
    }

刪除區間內的元素

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;
    }

輸出流

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();
    }

獲取從index開始的迭代器

/* @throws IndexOutOfBoundsException {@inheritDoc}
     */
    public synchronized ListIterator<E> listIterator(int index) {
        if (index < 0 || index > elementCount)
            throw new IndexOutOfBoundsException("Index: "+index);
        return new ListItr(index);
    }

獲取所有元素的迭代器

public synchronized ListIterator<E> listIterator() {
        return new ListItr(0);
    }

獲取所有元素的迭代器

public synchronized Iterator<E> iterator() {
        return new Itr();
    }

ListItr迭代器與Itr迭代器區別
ListItr繼承Itr，並增加了前驅遍歷的方法，也可以新增元素
Itr只能向後遍歷
可以檢視下面的程式碼

Itr

private class Itr implements Iterator<E> {
        int cursor;       // index of next element to return
        int lastRet = -1; // index of last element returned; -1 if no such
        int expectedModCount = modCount;

        public boolean hasNext() {
            // Racy but within spec, since modifications are checked
            // within or after synchronization in next/previous
            return cursor != elementCount;
        }

        public E next() {
            synchronized (Vector.this) {
                checkForComodification();
                int i = cursor;
                if (i >= elementCount)
                    throw new NoSuchElementException();
                cursor = i + 1;
                return elementData(lastRet = i);
            }
        }

        public void remove() {
            if (lastRet == -1)
                throw new IllegalStateException();
            synchronized (Vector.this) {
                checkForComodification();
                Vector.this.remove(lastRet);
                expectedModCount = modCount;
            }
            cursor = lastRet;
            lastRet = -1;
        }

        final void checkForComodification() {
            if (modCount != expectedModCount)
                throw new ConcurrentModificationException();
        }
    }

ListItr

final class ListItr extends Itr implements ListIterator<E> {
        ListItr(int index) {
            super();
            cursor = index;
        }

        public boolean hasPrevious() {
            return cursor != 0;
        }

        public int nextIndex() {
            return cursor;
        }

        public int previousIndex() {
            return cursor - 1;
        }

        public E previous() {
            synchronized (Vector.this) {
                checkForComodification();
                int i = cursor - 1;
                if (i < 0)
                    throw new NoSuchElementException();
                cursor = i;
                return elementData(lastRet = i);
            }
        }

        public void set(E e) {
            if (lastRet == -1)
                throw new IllegalStateException();
            synchronized (Vector.this) {
                checkForComodification();
                Vector.this.set(lastRet, e);
            }
        }

        public void add(E e) {
            int i = cursor;
            synchronized (Vector.this) {
                checkForComodification();
                Vector.this.add(i, e);
                expectedModCount = modCount;
            }
            cursor = i + 1;
            lastRet = -1;
        }
    }