JDK源码分析(5)Vector

JDK版本

Vector简介

/**
 * The {@code Vector} class implements a growable array of
 * objects. Like an array, it contains components that can be
 * accessed using an integer index. However, the size of a
 * {@code Vector} can grow or shrink as needed to accommodate
 * adding and removing items after the {@code Vector} has been created.
 *
 * <p>Each vector tries to optimize storage management by maintaining a
 * {@code capacity} and a {@code capacityIncrement}. The
 * {@code capacity} is always at least as large as the vector
 * size; it is usually larger because as components are added to the
 * vector, the vector's storage increases in chunks the size of
 * {@code capacityIncrement}. An application can increase the
 * capacity of a vector before inserting a large number of
 * components; this reduces the amount of incremental reallocation.
 *
 * <p><a name="fail-fast">
 * The iterators returned by this class's {@link #iterator() iterator} and
 * {@link #listIterator(int) listIterator} methods are <em>fail-fast</em></a>:
 * if the vector is structurally modified at any time after the iterator is
 * created, in any way except through the iterator's own
 * {@link ListIterator#remove() remove} or
 * {@link ListIterator#add(Object) add} methods, the iterator will throw a
 * {@link ConcurrentModificationException}.  Thus, in the face of
 * concurrent modification, the iterator fails quickly and cleanly, rather
 * than risking arbitrary, non-deterministic behavior at an undetermined
 * time in the future.  The {@link Enumeration Enumerations} returned by
 * the {@link #elements() elements} method are <em>not</em> fail-fast.
 *
 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
 * as it is, generally speaking, impossible to make any hard guarantees in the
 * presence of unsynchronized concurrent modification.  Fail-fast iterators
 * throw {@code ConcurrentModificationException} on a best-effort basis.
 * Therefore, it would be wrong to write a program that depended on this
 * exception for its correctness:  <i>the fail-fast behavior of iterators
 * should be used only to detect bugs.</i>
 *
 * <p>As of the Java 2 platform v1.2, this class was retrofitted to
 * implement the {@link List} interface, making it a member of the
 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
 * Java Collections Framework</a>.  Unlike the new collection
 * implementations, {@code Vector} is synchronized.  If a thread-safe
 * implementation is not needed, it is recommended to use {@link
 * ArrayList} in place of {@code Vector}.
 *
 * @author  Lee Boynton
 * @author  Jonathan Payne
 * @see Collection
 * @see LinkedList
 * @since   JDK1.0
 */

首先,Vector 是一个可增长的数组(和 ArrayList 类似),能够用索引直接找到元素,Vector 的容量可增可减

其次,Vector 使用变量 capacitycapacityIncrement 来进行容量的管理,关于容量和大小的说法,之前也提到过,容量是最多能够容纳多少元素,而大小是目前容纳了多少元素。capacity 指的就是容量,是永远大于或等于 Vector 的大小的,不过容量通常是大于 Vector 的大小的,因为它扩容的方式有点特殊,下文提及,在插入大量数据之前,最好能进行适当的扩容,避免了再分配的时间浪费

Vector 是线程安全的,它所有的方法都加上了 synchronized 关键字。

源码分析

package java.util;

public class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
	 //保存Vector中的数据的数组
    protected Object[] elementData;

	 // 实际数据的长度
    protected int elementCount;

	 //容量增长系数
    protected int capacityIncrement;

    /** use serialVersionUID from JDK 1.0.2 for interoperability */
	//Vector的版本序号
    private static final long serialVersionUID = -2767605614048989439L;

	 // Vector有参构造函数,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: "+
		//新建一个数组,数组容量是initialCapacity										initialCapacity);
        this.elementData = new Object[initialCapacity];
        //设置容量增长系数
		this.capacityIncrement = capacityIncrement;
    }

	 // Vector有参构造函数,容量大小的构造函数
    public Vector(int initialCapacity) {
        this(initialCapacity, 0);
    }

	 //Vector无参构造函数,默认容量为10
    public Vector() {
        this(10);
    }
	
	 //Vector有参构造函数,指定集合的Vector构造函数
    public Vector(Collection<? extends E> c) {
        //获取“集合(c)”的数组,并将其赋值给elementData
		elementData = c.toArray();
        //设置数组长度
		elementCount = elementData.length;
        // c.toArray might (incorrectly) not return Object[] (see 6260652)
        
		if (elementData.getClass() != Object[].class)
            elementData = Arrays.copyOf(elementData, elementCount, Object[].class);
    }

    // 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);
    }

    // 将当前容量值设为 = 实际元素个数  
    public synchronized void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (elementCount < oldCapacity) {
            elementData = Arrays.copyOf(elementData, elementCount);
        }
    }

    // 确定Vector的容量
    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);
    }

    //设置最大数组长度
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;

    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;
    }

    // 设置容量值为 newSize  
    public synchronized void setSize(int newSize) {
        modCount++;
        if (newSize > elementCount) {
			// 若 "newSize 大于 Vector容量",则调整Vector的大小。 
            ensureCapacityHelper(newSize);
        } else {
			// 若 "newSize 小于/等于 Vector容量",则将newSize位置开始的元素都设置为null  
            for (int i = newSize ; i < elementCount ; i++) {
                elementData[i] = null;
            }
        }
        elementCount = newSize;
    }

    // 返回“Vector的总的容量”  
    public synchronized int capacity() {
        return elementData.length;
    }

    // 返回“Vector的实际大小”,即Vector中元素个数 
    public synchronized int size() {
        return elementCount;
    }

    // 判断Vector是否为空 
    public synchronized boolean isEmpty() {
        return elementCount == 0;
    }

    // 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");
            }
        };
    }

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

    // 从index位置开始向后查找元素(o)。  
    // 若找到,则返回元素的索引值;否则,返回-1  
    public synchronized int indexOf(Object o, int index) {
        if (o == null) {
			// 若查找元素为null,则正向找出null元素,并返回它对应的序号  
            for (int i = index ; i < elementCount ; i++)
                if (elementData[i]==null)
                    return i;
        } else {
			// 若查找元素不为null,则正向找出该元素,并返回它对应的序号
            for (int i = index ; i < elementCount ; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

    // 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);
    }

    // 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) {
			// 若查找元素为null,则反向找出null元素,并返回它对应的序号
            for (int i = index; i >= 0; i--)
                if (elementData[i]==null)
                    return i;
        } else {
			// 若查找元素不为null,则反向找出该元素,并返回它对应的序号 
            for (int i = index; i >= 0; i--)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }

    // 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);
    }

    // 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);
    }

    // 获取Vector中的最后一个元素。  
    // 若失败,则抛出异常!  
    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++;
        // Let gc do its work
		// 将Vector中的全部元素设为null 
        for (int i = 0; i < elementCount; i++)
            elementData[i] = null;

        elementCount = 0;
    }
	
	//@SuppressWarnings注解用于抑制编译器产生警告信息。
    // 克隆函数
    public synchronized Object clone() {
        try {
            @SuppressWarnings("unchecked")
                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(e);
        }
    }

    // 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
    @SuppressWarnings("unchecked")
    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;
    }

    // Positional Access Operations

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

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

        return 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);

        E oldValue = elementData(index);
        elementData[index] = element;
        return 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);
        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Vector
    public void clear() {
        removeAllElements();
    }

    // Bulk Operations

    // 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;
    }

    //从文件中读取数据,放到Vector中
    private void readObject(ObjectInputStream in)
            throws IOException, ClassNotFoundException {
        ObjectInputStream.GetField gfields = in.readFields();
        int count = gfields.get("elementCount", 0);
        Object[] data = (Object[])gfields.get("elementData", null);
        if (count < 0 || data == null || count > data.length) {
            throw new StreamCorruptedException("Inconsistent vector internals");
        }
        elementCount = count;
        elementData = data.clone();
    }

    // java.io.Serializable的写入函数
    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();
    }

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

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

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

    //迭代器内部类
    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;
        }

        @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();
        }
    }

    /**
     * An optimized version of AbstractList.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;
        }
    }

    @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();
        }
    }

    @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);
        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();
        }

        // shift surviving elements left over the spaces left by removed elements
        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;
    }

    @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++;
    }

    @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; // -1 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;
        }
    }
}

posted @ 2018-12-20 00:35  Tu9oh0st  阅读(269)  评论(0编辑  收藏  举报