java基础：Vector

#Java篇/基础

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