Vector源码详解

       Vector和ArrayList类似，也是基于动态数组实现的。Vector是JDK1.0引入了，它的很多实现方法都加入了同步语句，因此是线程安全的（其实也只是相对安全，有些时候还是要加入同步语句来保证线程的安全），可以用于多线程环境。Vector实现了Serializable接口，因此它支持序列化，实现了Cloneable接口，能被克隆，实现了RandomAccess接口，支持快速随机访问。

    

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


public class Vector<E>
    extends AbstractList<E>
    implements List<E>, RandomAccess, Cloneable, java.io.Serializable
{
    //Vector基于此数组实现
    protected Object[] elementData;
    
    //实际元素的数量
    protected int elementCount;

    //增长系数
    protected int capacityIncrement;

    //版本序列号
    private static final long serialVersionUID = -2767605614048989439L;

    //指定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);
        this.elementData = new Object[initialCapacity];
        this.capacityIncrement = capacityIncrement;
    }

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

    //构造函数，默认容量是10
    public Vector() {
        this(10);
    }

    //包含指定集合的构造函数
    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);
    }

    //将Vector中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Vector的容量值设为其实际元素个数
    public synchronized void trimToSize() {
        modCount++;
        int oldCapacity = elementData.length;
        if (elementCount < oldCapacity) {
            elementData = Arrays.copyOf(elementData, elementCount);
        }
    }

    //确保Vector的容量
    public synchronized void ensureCapacity(int minCapacity) {
        if (minCapacity > 0) {
            modCount++;
            ensureCapacityHelper(minCapacity);
        }
    }

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

    //建议为Vector分配的最大容量
    private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
    
    
    private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        //当容量增量系数大于0时，容量按增量系数来增加
        //否则(容量增量系数小于等于0)，容量增加一倍
        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;
    }

    //设置实际元素数量为指定值
    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;
    }

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

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

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

    //返回Vector对应的Enumeration
    public Enumeration<E> elements() {
        return new Enumeration<E>() {
            int count = 0;
            //判断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");
            }
        };
    }

    //判断Vector中是否包含指定对象
    public boolean contains(Object o) {
        return indexOf(o, 0) >= 0;
    }

    //从前往后查找，返回指定对象在Vector中的索引值 
    //如果Vector不包含该对象，则返回-1
    public int indexOf(Object o) {
        return indexOf(o, 0);
    }

    //从index位置开始往后查找指定元素
    //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) {
            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;
    }

    //从末尾往前查找，返回指定对象的索引值
    //若找不到，则返回-1
    public synchronized int lastIndexOf(Object o) {
        return lastIndexOf(o, elementCount-1);
    }

    //从index位置开始，由后往前依次查找对象(o)
    //若找到，则返回该对象的索引值，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;
    }

    //返回Vector中index位置的元素
    //若index越界，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
    public synchronized E firstElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(0);
    }

    //返回Vector中的最后一个元素
    public synchronized E lastElement() {
        if (elementCount == 0) {
            throw new NoSuchElementException();
        }
        return elementData(elementCount - 1);
    }

    //设置index位置的元素为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 与ArrayList类似
    }

    //在Vector中index位置处插入指定元素
    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++;
    }

   //在Vector中加入指定元素
    public synchronized void addElement(E obj) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = obj;
    }

    //从Vector中移除指定元素
    //移除成功，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;
    }

    //清除掉Vector中的所有元素
    public synchronized void removeAllElements() {
        modCount++;
        // Let gc do its work
        for (int i = 0; i < elementCount; i++)
            elementData[i] = null;

        elementCount = 0;
    }

    //对Vector对象进行克隆
    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);
        }
    }

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

   
    @SuppressWarnings("unchecked")
    //返回Vector的模板数组
    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;
    }

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

    //返回Vector中index位置处的数组
    public synchronized E get(int index) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

        return elementData(index);
    }

    //设置Vector中index位置为指定的元素
    public synchronized E set(int index, E element) {
        if (index >= elementCount)
            throw new ArrayIndexOutOfBoundsException(index);

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

    //将指定元素添加到Vector中
    public synchronized boolean add(E e) {
        modCount++;
        ensureCapacityHelper(elementCount + 1);
        elementData[elementCount++] = e;
        return true;
    }

    //从Vector删除指定对象
    public boolean remove(Object o) {
        return removeElement(o);
    }

    //在Vector的index位置添加指定对象
    public void add(int index, E element) {
        insertElementAt(element, index);
    }

    //删除并返回index位置的元素
    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();
    }

    //判断Vector中是否包含指定集合
    public synchronized boolean containsAll(Collection<?> c) {
        return super.containsAll(c);
    }

    //将指定集合添加到Vector中
    public synchronized boolean addAll(Collection<? extends E> c) {
        modCount++;
        Object[] a = c.toArray();
        int numNew = a.length;
        ensureCapacityHelper(elementCount + numNew);
        System.arraycopy(a, 0, elementData, elementCount, numNew);
        elementCount += numNew;
        return numNew != 0;
    }

    //从Vector中删除指定集合的全部元素
    public synchronized boolean removeAll(Collection<?> c) {
        return super.removeAll(c);
    }

    //Vector中只保留指定集合的全部元素(其他的元素都删除)
    public synchronized boolean retainAll(Collection<?> c) {
        return super.retainAll(c);
    }

    //从index位置开始，将集合添加到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;
    }

    //判断两个对象是否相等
    public synchronized boolean equals(Object o) {
        return super.equals(o);
    }

    //返回hash值
    public synchronized int hashCode() {
        return super.hashCode();
    }

   //返回字符串
    public synchronized String toString() {
        return super.toString();
    }

    
    public synchronized List<E> subList(int fromIndex, int toIndex) {
        return Collections.synchronizedList(super.subList(fromIndex, toIndex),
                                            this);
    }

    //移除Vector中指定范围内的元素
    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;
    }

    //
    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ListIterator
    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);
    }

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

    
    //An optimized version of AbstractList.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;
        }

        @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();
            }
        }
        //fail-fast机制
        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++;
    }
    
    
}

总结

1.Vector的很多方法是synchronized的，除此之外与ArrayList基本是相似的。

2.Vector因为是同步的，所以效率比ArrayList要低。