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Java源代码分析之Vector数组

来源：程序员人生发布时间：2016-07-28 08:41:30 阅读次数：2089次

Vector源码分析

每一个Java程序员应当的特性
- 可变长数组（grow or shrink）
- 能够使用索引获得值（accessed using an integer index）
- 多线程环境下线程安全
类图

package java.util;

import java.util.function.Consumer;
import java.util.function.Predicate;
import java.util.function.UnaryOperator;

/*
vector 通过capacity（容量）和capacityIncrement（增量）两个属性来最化管理存储， capacity 1般都比 size 大。 
当知道需要插入大量元素时，可以提早分配给vector较大空间，减少分配内存次数， 从而减少没必要要的开消。 
此类的iterator和listIterator方法返回的迭代器是快速失败的：如果该向量在任什么时候间从结构上修改创建迭代器后，
以任何方式，除通过迭代器本身的remove或add方法，迭代器都将抛出ConcurrentModificationException。
因此，在并发的修改，迭代器很快就会完全失败，而不是在将来不肯定的时间任意冒险，不肯定性的行动。
通过elements方法返回的Enumeration不是快速失败的。
注意，迭代器的快速失败行动不能得到保证，由于它是，1般来讲，
不可能作出任何硬性保证不同步并发修改的存在。快速失败迭代器抛出ConcurrentModificationException尽最大努力的基础上。
因此，这将是毛病的编写1个程序，依赖于此异常为它的正确性：
迭代器的快速失败行动应当仅用于检测bug。
从Java 2平台v1.2，这个类是改进来实现List接口，使它成为Java Collections Framework的成员。
不同的是新的集合实现不同，Vector是同步的。
如果不需要线程安全履行，建议代替矢量的使用的ArrayList。
 */
public class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    // 寄存数据的数组
    protected Object[] elementData;

    // 实际元素个数
    protected int elementCount;

    // 容量增量，每次扩容增加的大小，如果 capacityIncrement小雨或等于0，那末容量会每次翻倍double的增长
    protected int capacityIncrement;

    private static final long serialVersionUID = -2767605614048989439L;
// 数组的初始化，增量的初始化，容量小于0会报异常
    public Vector(int initialCapacity, int capacityIncrement) {
        super();
        if (initialCapacity < 0)
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        this.elementData = new Object[initialCapacity];
        this.capacityIncrement = capacityIncrement;
    }

    // 指定容量，并且增量为0，每次扩容方法为翻倍
    public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }

    //默许构造方法，默许容量大小为10
    public Vector() {
        this(10);
    }

    // 根据指定集合创建vector
    // 另外vector的顺序由集合Collection的iterator遍历的顺序来保证
    public Vector(Collection<? extends E> c) {
        elementData = c.toArray();  // 根据集合生成数组，数组是reallocate的，不存在refer关系
        elementCount = elementData.length;
        //下面1句话简单理解就是 toArray（）返回的其实不1定是Object[]数组（实际类型）
        // 具体请看 我的博客文章 http://blog.csdn.net/huzhigenlaohu/article/details/51702737
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
    }

    /**
     * anArray 为空会报空指针异常 ， anArray的长度不能容纳elementData所有元素汇会报索引越界异常
     * 另外 c.toArray  not return Object[]时候 报 ArrayStoreException
     * 请看 http://blog.csdn.net/huzhigenlaohu/article/details/51702737
     */
    public synchronized void copyInto(Object[] anArray) {
        System.arraycopy(elementData, 0, anArray, 0, elementCount);
    }

    // 去掉Vector 数组后面未存入数据的部份，使得Capacity（length） = elementCount
    public synchronized void trimToSize() {
        //这个 字段含义为 vector 结构（1般指的是大小）被修改的次数
        modCount++;
        int oldCapacity = elementData.length;
        if (elementCount < oldCapacity) {
            elementData = Arrays.copyOf(elementData, elementCount);
        }
    }
//扩容函数（对外暴露的函数，实现看grow）
    public synchronized void ensureCapacity(int minCapacity) {
        if (minCapacity > 0) {
            modCount++;
            ensureCapacityHelper(minCapacity);
        }
    }


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


    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
     //这个才是看的重点，上面两个函数可以疏忽掉。。。额，说错了，不是疏忽掉而是可以不看
    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        // 如果增量大于0那末是的容量+Increment，如果小于等于0，那末容量翻倍
        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?
                                         capacityIncrement : oldCapacity);
        // 如果根据扩容方法后容量还是小于minCapacity，那末设置扩容后大小为minCapacity
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        //溢出，大于最大允许的容量
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        //根据容量重新reallocate内存，得到1个新数组
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
// 容量超过最大值处理方式
    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vector 的size大小，注意其实不是length，当设置的newsize大于当前的size那末斟酌是不是要扩容，如果小于，那末把过剩的部份全部设置为null
    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;
    }

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

    //元素个数
    public synchronized int size() {
        return elementCount;
    }

    //实际存储的元素是不是为空
    public synchronized boolean isEmpty() {
        return elementCount == 0;
    }

    //根据索引生成 对应元素的枚举 ，索引为0 为枚举第1个元素，索引为1为枚举第2个元素，and so on
    public Enumeration<E> elements() {
        return new Enumeration<E>() {
            int count = 0;

            public boolean hasMoreElements() {
                return count < elementCount;
            }
//可以看到此方法会抛出异常，在调用的时候务必先调用hasMoreElements进行判断
            public E nextElement() {
                //提供vector对象锁，保持同步
                synchronized (Vector.this) {
                    if (count < elementCount) {
                        return elementData(count++);
                    }
                }
                throw new NoSuchElementException("Vector Enumeration");
            }
        };
    }

    //辨别是不是存在对象 o
    public boolean contains(Object o) {
        return indexOf(o, 0) >= 0;
    }

    //返回第1个出现o的位置索引
    public int indexOf(Object o) {
        return indexOf(o, 0);
    }

//主要是判断o是不是为空，其他都是顺序查找，很简单O（n）
    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;
    }
//从数组后端开始查找起，出现的第1个元素
    public synchronized int lastIndexOf(Object o) {
        return lastIndexOf(o, elementCount-1);
    }
//主要是判断o是不是为空，其他都是顺序查找，很简单O（n）
    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;
    }

    //方法同等于List接口的get（i）方法说
    public synchronized E elementAt(int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " + elementCount);
        }

        return elementData(index);
    }

    public synchronized E firstElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(0);
    }
    public synchronized E lastElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(elementCount - 1);
    }

    public synchronized void setElementAt(E obj, int index) {
        if (index >= elementCount) {
            throw new ArrayIndexOutOfBoundsException(index + " >= " +
                                                     elementCount);
        }
        elementData[index] = obj;
    }

    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 */
    }

    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++;
    }

    public synchronized void addElement(E obj) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = obj;
    }

    //删除从数组左侧起第1个与obj相等的元素
    public synchronized boolean removeElement(Object obj) {
        modCount++;
        int i = indexOf(obj);
        if (i >= 0) {
            removeElementAt(i);
            return true;
        }
        return false;
    }

    //删除所有元素
    public synchronized void removeAllElements() {
        modCount++;
        // Let gc do its work
        for (int i = 0; i < elementCount; i++)
            elementData[i] = null; //gc垃圾回收

        elementCount = 0;
    }

    // clone克隆Vector，重新生成的数组与原来的数组属于不同援用，重新分配内存
    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(e);
        }
    }
    public synchronized Object[] toArray() {
        return Arrays.copyOf(elementData, elementCount);
    }

    @SuppressWarnings("unchecked")
    public synchronized <T> T[] toArray(T[] a) {//泛型指定生成的数组的类型
        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;
    }
//没同步，也没判断会不会抛出异常，为何会存在呢？由于这个方法外部不能调用，它由其他内部（public）同步方法调用，保证线程安全
    @SuppressWarnings("unchecked")
    E elementData(int index) {
        return (E) elementData[index];
    }
    public synchronized E get(int index) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        return elementData(index);
    }

//返回的是旧值
    public synchronized E set(int index, E element) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

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

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

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

    public void add(int index, E element) {
        insertElementAt(element, index);
    }

//返回被移除的对象
    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();
    }

    // 批量操作，判断vector中是不是包括集合
    // 特别注意：判断集合集合中每一个元素是不是都存在vector中，并没有顺序可言，单独判断，复杂度为O（m*n）
    public synchronized boolean containsAll(Collection<?> c) {
        return super.containsAll(c);
        // 父类方法AbstractCollection
        /*
        public boolean containsAll(Collection<?> c) {
        for (Object e : c)
            if (!contains(e))
                return false;
            return true;
       }
       */
    }

    //集合到vector中，会抛出空指针异常
    //特别注意：当正在进行此操作的时候，集合C又被另外1个线程修改，那末得到的vector是不肯定的
    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;
    }

   // 删除指定集合中切存在于vector中的元素
    // 遍历vector中每一个元素，判断是不是存在于collection中，存在则删除，复杂度为O（M*n）
    public synchronized boolean removeAll(Collection<?> c) {
        return super.removeAll(c);
    }

   // 与前面1个函数功能相反，保存存在于Collection中的vector的元素
    public synchronized boolean retainAll(Collection<?> c) {
        return super.retainAll(c);
    }

   //指定索引，插入集合
    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;
    }

    // 顺序、值、大小都要相等，使用父类AbstractList方法实现，顺序由listIterator()保证
    public synchronized boolean equals(Object o) {
        return super.equals(o);
    }
    public synchronized int hashCode() {
        return super.hashCode();
    }
    public synchronized String toString() {
        return super.toString();
    }
    //AbstractCollection方法
/*
public String toString() {
        Iterator<E> it = iterator();
        if (! it.hasNext())
            return "[]";

        StringBuilder sb = new StringBuilder();
        sb.append('[');
        for (;;) {
            E e = it.next();
            sb.append(e == this ? "(this Collection)" : e);
            if (! it.hasNext())
                return sb.append(']').toString();
            sb.append(',').append(' ');
        }
    }
*/
    // 根据指定索引，返回子集合
    //特别注意： 返回的子集合还是依赖于此vector的，其实不是重新分配内存的
    //对子集合的1切操作将会影响vector的变化，比如对子集合的排序（这个利用的非常广）、清空子集合等都会影响vector元素变化，但是与此同时也要斟酌到多线程的不肯定性
    //eg:list.subList(from, to).clear();清空
    //由于使用了Collections.synchronizedList进行同步处理（对象锁为当前vector对象），因此对vector的操作和对子集合的操作是同步处理的
    public synchronized List<E> subList(int fromIndex, int toIndex) {
        return Collections.synchronizedList(super.subList(fromIndex, toIndex),
                                            this);
    }

   //删除指定范围子集合
    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;
    }

    //序列化
    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();
    }

    // 返回指定游标的列表迭代器，此迭代器ListIterator可以向前向后迭代，比普通iterator()方法强大Itr，推荐使用
    public synchronized ListIterator<E> listIterator(int index) {
        if (index < 0 || index > elementCount)
            throw new IndexOutOfBoundsException("Index: "+index);
        return new ListItr(index);
    }

    //同上1个方法，默许游标位置为起始位置0
    public synchronized ListIterator<E> listIterator() {
        return new ListItr(0);
    }

    //返回1个迭代器
    public synchronized Iterator<E> iterator() {
        return new Itr();
    }

    /**
     * An optimized version of AbstractList.Itr
     */
     //迭代器默许实现，会出现fail-fast机制
    private class Itr implements Iterator<E> {
        int cursor;       // index of next element to return
        int lastRet = -1; // index of last element returned; ⑴ 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();//检查在迭代期间，检查vector是不是存在结构修改
                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;
        }

        @Override
        public void forEachRemaining(Consumer<? super E> action) {
            Objects.requireNonNull(action);
            synchronized (Vector.this) {
                final int size = elementCount;
                int i = cursor;
                if (i >= size) {
                    return;
                }
        @SuppressWarnings("unchecked")
                final E[] elementData = (E[]) Vector.this.elementData;
                if (i >= elementData.length) {
                    throw new ConcurrentModificationException();
                }
                while (i != size && modCount == expectedModCount) {
                    action.accept(elementData[i++]);
                }
                // update once at end of iteration to reduce heap write traffic
                cursor = i;
                lastRet = i - 1;
                checkForComodification();
            }
        }

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

    //列表迭代器，可以向前向后遍历
    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;
        }
    }
//jdk1.8 新加入的方法，遍历vector中每一个元素，并利用于action行动，支持lambda表达式
    @Override
    public synchronized void forEach(Consumer<? super E> action) {
        Objects.requireNonNull(action);
        final int expectedModCount = modCount;
        @SuppressWarnings("unchecked")
        final E[] elementData = (E[]) this.elementData;
        final int elementCount = this.elementCount;
        for (int i=0; modCount == expectedModCount && i < elementCount; i++) {
            action.accept(elementData[i]);
        }
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
    }
//支持lambda表达式，判断是不是复合某种条件，然后做其他操作
    @Override
    @SuppressWarnings("unchecked")
    public synchronized boolean removeIf(Predicate<? super E> filter) {
        Objects.requireNonNull(filter);
        // figure out which elements are to be removed
        // any exception thrown from the filter predicate at this stage
        // will leave the collection unmodified
        int removeCount = 0;
        final int size = elementCount;
        final BitSet removeSet = new BitSet(size);//位集合，记录符合条件的元素的索引
        final int expectedModCount = modCount;
        for (int i=0; modCount == expectedModCount && i < size; i++) {
            @SuppressWarnings("unchecked")
            final E element = (E) elementData[i];
            if (filter.test(element)) {
                removeSet.set(i);
                removeCount++;
            }
        }
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }

        //删除符合条件的元素，左移
        final boolean anyToRemove = removeCount > 0;
        if (anyToRemove) {
            final int newSize = size - removeCount;
            for (int i=0, j=0; (i < size) && (j < newSize); i++, j++) {
                i = removeSet.nextClearBit(i);
                elementData[j] = elementData[i];
            }
            for (int k=newSize; k < size; k++) {
                elementData[k] = null;  // Let gc do its work
            }
            elementCount = newSize;
            if (modCount != expectedModCount) {
                throw new ConcurrentModificationException();
            }
            modCount++;
        }

        return anyToRemove;
    }
//支持lambda表达式,对全部元素进行替换操作
    @Override
    @SuppressWarnings("unchecked")
    public synchronized void replaceAll(UnaryOperator<E> operator) {
        Objects.requireNonNull(operator);
        final int expectedModCount = modCount;
        final int size = elementCount;
        for (int i=0; modCount == expectedModCount && i < size; i++) {
            elementData[i] = operator.apply((E) elementData[i]);
        }
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
        modCount++;
    }
// Arrays.sort 排序
    @SuppressWarnings("unchecked")
    @Override
    public synchronized void sort(Comparator<? super E> c) {
        final int expectedModCount = modCount;
        Arrays.sort((E[]) elementData, 0, elementCount, c);
        if (modCount != expectedModCount) {
            throw new ConcurrentModificationException();
        }
        modCount++;
    }

    /**
     * Creates a <em><a href="Spliterator.html#binding">late-binding</a></em>
     * and <em>fail-fast</em> {@link Spliterator} over the elements in this
     * list.
     *
     * <p>The {@code Spliterator} reports {@link Spliterator#SIZED},
     * {@link Spliterator#SUBSIZED}, and {@link Spliterator#ORDERED}.
     * Overriding implementations should document the reporting of additional
     * characteristic values.
     *
     * @return a {@code Spliterator} over the elements in this list
     * @since 1.8
     */
    @Override
    public Spliterator<E> spliterator() {
        return new VectorSpliterator<>(this, null, 0, -1, 0);
    }

    /** Similar to ArrayList Spliterator */
    static final class VectorSpliterator<E> implements Spliterator<E> {
        private final Vector<E> list;
        private Object[] array;
        private int index; // current index, modified on advance/split
        private int fence; // ⑴ until used; then one past last index
        private int expectedModCount; // initialized when fence set

        /** Create new spliterator covering the given  range */
        VectorSpliterator(Vector<E> list, Object[] array, int origin, int fence,
                          int expectedModCount) {
            this.list = list;
            this.array = array;
            this.index = origin;
            this.fence = fence;
            this.expectedModCount = expectedModCount;
        }

        private int getFence() { // initialize on first use
            int hi;
            if ((hi = fence) < 0) {
                synchronized(list) {
                    array = list.elementData;
                    expectedModCount = list.modCount;
                    hi = fence = list.elementCount;
                }
            }
            return hi;
        }

        public Spliterator<E> trySplit() {
            int hi = getFence(), lo = index, mid = (lo + hi) >>> 1;
            return (lo >= mid) ? null :
                new VectorSpliterator<E>(list, array, lo, index = mid,
                                         expectedModCount);
        }

        @SuppressWarnings("unchecked")
        public boolean tryAdvance(Consumer<? super E> action) {
            int i;
            if (action == null)
                throw new NullPointerException();
            if (getFence() > (i = index)) {
                index = i + 1;
                action.accept((E)array[i]);
                if (list.modCount != expectedModCount)
                    throw new ConcurrentModificationException();
                return true;
            }
            return false;
        }

        @SuppressWarnings("unchecked")
        public void forEachRemaining(Consumer<? super E> action) {
            int i, hi; // hoist accesses and checks from loop
            Vector<E> lst; Object[] a;
            if (action == null)
                throw new NullPointerException();
            if ((lst = list) != null) {
                if ((hi = fence) < 0) {
                    synchronized(lst) {
                        expectedModCount = lst.modCount;
                        a = array = lst.elementData;
                        hi = fence = lst.elementCount;
                    }
                }
                else
                    a = array;
                if (a != null && (i = index) >= 0 && (index = hi) <= a.length) {
                    while (i < hi)
                        action.accept((E) a[i++]);
                    if (lst.modCount == expectedModCount)
                        return;
                }
            }
            throw new ConcurrentModificationException();
        }

        public long estimateSize() {
            return (long) (getFence() - index);
        }

        public int characteristics() {
            return Spliterator.ORDERED | Spliterator.SIZED | Spliterator.SUBSIZED;
        }
    }
}

Vector使用案例

subList() 用法

/**
 * Created by Genge on 2016-06⑴9.
 */
public class Solution {
    public static void main(String[] args) {
        Vector<String> vector = new Vector<String>();
        vector.add("Genge");
        vector.add("Hello");
        vector.add("World");
        System.out.println("处理前的结果：");
        Iterator<String> iterator = vector.iterator();
        while (iterator.hasNext()) {
            System.out.println(iterator.next());
        }

        List<String> sublist = vector.subList(1, 2);

        sublist.clear();

        sublist.add("SB");
        sublist.add("Huangdou");

        System.out.println("处理后结果：");
        Iterator<String> iter = vector.iterator();
        while (iter.hasNext()) {
            System.out.println(iter.next());
        }
    }
}

结果图以下:

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