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

 

实例变量

//保存元素的容器protected Object[] elementData;//元素的数量protected int elementCount;//容器扩容时的增量protected int capacityIncrement;

 

4个构造器

//初始容量和容器扩容增量的构造器public Vector(int initialCapacity, int capacityIncrement) {        super();        if (initialCapacity < 0)            throw new IllegalArgumentException("Illegal Capacity: "+                                               initialCapacity);        this.elementData = new Object[initialCapacity];        this.capacityIncrement = capacityIncrement;}//只有初始容量的构造器,默认使用容器扩容增量为0,表示不指定,那么扩容时会变成原容量的2倍public Vector(int initialCapacity) {        this(initialCapacity, 0);}不指定初始容量,那么默认初始容量为10public Vector() {        this(10);}//使用c构造Vectorpublic Vector(Collection
      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);}

 

扩容方法

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 void grow(int minCapacity) {        // overflow-conscious code        int oldCapacity = elementData.length;        int newCapacity = oldCapacity + ((capacityIncrement > 0) ?                                         capacityIncrement : oldCapacity);//如果capacityIncrement为0,那么newCapacity为oldCapacity * 2        if (newCapacity - minCapacity < 0)            newCapacity = minCapacity;        if (newCapacity - MAX_ARRAY_SIZE > 0)            newCapacity = hugeCapacity(minCapacity);        elementData = Arrays.copyOf(elementData, newCapacity);}

 

设置容量

public synchronized void setSize(int newSize) {        modCount++;        if (newSize > elementCount) {
   //如果新容量大于旧容量,扩容            ensureCapacityHelper(newSize);        } else {
   //否则,将超过新容量的部分都设置为null,注意容量没变,只是超出newSize的元素变成null            for (int i = newSize ; i < elementCount ; i++) {                elementData[i] = null;            }        }        elementCount = newSize;}

 

2个迭代器，一个从头迭代到尾，一个从尾迭代到头

private class Itr implements Iterator
     
       {//正向迭代器,cursor为0        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
       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();        }}
     

 

final class ListItr extends Itr implements ListIterator
     
       {//从index到头迭代        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
       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();        }}
     

 

//index指定从哪个位置开始往前迭代public synchronized ListIterator
     
       listIterator(int index) {        if (index < 0 || index > elementCount)            throw new IndexOutOfBoundsException("Index: "+index);        return new ListItr(index);}
     

 

Vector是线程安全的，它的方法使用synchronized修饰，如果不需要线程安全，推荐使用ArrayList代替。