Vector实现了AbstractList抽象类和List接口,和ArrayList一样是基于Array存储的

Vector 是线程安全的,在大多数方法上存在synchronized关键字

//Vector存放的元素,初始化默认长度为10

protected Object[] elementData;

//元素个数

protected int elementCount;

//每次扩容大小,默认为0

protected int capacityIncrement;

//构造函数，无指定初始化大小和无扩容大小

public Vector() {

    this(10);

}

//构造函数，指定初始化大小和无扩容大小

public Vector(int initialCapacity) {

    this(initialCapacity, 0);

}

//构造函数，指定初始化大小和扩容大小

public Vector(int initialCapacity, int capacityIncrement) {

    super();

    if (initialCapacity < 0)

        throw new IllegalArgumentException("Illegal Capacity: "+

                                           initialCapacity);

    this.elementData = new Object[initialCapacity];

    this.capacityIncrement = capacityIncrement;

}

//构造函数,Collection集合

public Vector(Collection<? extends E> c) {

    elementData = c.toArray();

    elementCount = elementData.length;

    if (elementData.getClass() != Object[].class)

        elementData = Arrays.copyOf(elementData, elementCount, Object[].class);

    }

//确保扩容的最小容量

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);

}

//扩容

private void grow(int minCapacity) {

    int oldCapacity = elementData.length;

    //当扩容大小为0的时候,扩容为原来的2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;

}

• ensureCapacity(int minCapacity)方法确保Vector的最小长度,当扩容2倍小于minCapacity时,扩容到minCapacity大小,minCapacity不能小于0
• 最大长度为2的31次方-1

设置大小

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;

}

• 超过大小的被设置为Null

public synchronized void copyInto(Object[] anArray) {

    System.arraycopy(elementData, 0, anArray, 0, elementCount);

}

public synchronized void trimToSize() {

    modCount++;

    int oldCapacity = elementData.length;

    if (elementCount < oldCapacity) {

        elementData = Arrays.copyOf(elementData, elementCount);

    }

}

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;

}

是否为空

public synchronized boolean isEmpty() {

    return elementCount == 0;

}

设置索引上的元素

public synchronized void setElementAt(E obj, int index) {

    if (index >= elementCount) {

        throw new ArrayIndexOutOfBoundsException(index + " >= " +

                                                 elementCount);

    }

    elementData[index] = obj;

}

添加元素

 public synchronized void addElement(E obj) {

    modCount++;

    ensureCapacityHelper(elementCount + 1);

    elementData[elementCount++] = obj;

}

• 扩容

插入元素

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++;

}

• 扩容
• 数组拷贝向索引后移动
• 删除为向前移动

删除元素

public synchronized boolean removeElement(Object obj) {

    modCount++;

    int i = indexOf(obj);

    if (i >= 0) {

        removeElementAt(i);

        return true;

    }

    return false;

}

• 只能删除第一个