ArrayList和Vector异同点

ArrayList和Vector异同点

相同点：

底层都是数组

代码语言：javascript复制

//ArrayList
transient Object[] elementData;

//Vector
protected Object[] elementData;

默认大小都是10

代码语言：javascript复制

//Vector
public Vector() {
    this(10);
}
//ArrayList
private static final int DEFAULT_CAPACITY = 10;
public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
            this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: " 
                                               initialCapacity);
        }
}

不同点

线程安全

代码语言：javascript复制

//ArrayList线程不安全，例如
public boolean add(E e) {
        ensureCapacityInternal(size   1);  // Increments modCount!!
        elementData[size  ] = e;
        return true;
}
//Vector线程安全，例如，加了synchronized关键字
public synchronized boolean add(E e) {
        modCount  ;
        ensureCapacityHelper(elementCount   1);
        elementData[elementCount  ] = e;
        return true;
}

扩容倍数

代码语言：javascript复制

//ArrayList  1.5倍
private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity   (oldCapacity >> 1);//1.5倍扩容
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        // minCapacity is usually close to size, so this is a win:
        elementData = Arrays.copyOf(elementData, newCapacity);
}
//Vector 2倍扩容
private void grow(int minCapacity) {
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity   ((capacityIncrement > 0) ?
                                         capacityIncrement : oldCapacity);//2倍扩容
        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        elementData = Arrays.copyOf(elementData, newCapacity);
}

arraylist vector 数组 线程安全

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