ArrayList中的一些小细节@JDK8

ArrayList中的一些小细节@JDK8

protected transient int modCount = 0;

当int发生整形溢出的时候会从重新开始，这样保证了在有限的操作次数内，对于不同操作的版本号一定会不相同

int k = Integer.MAX_VALUE;

for (; ; ) {

    System.out.println(k++);

    try {

        Thread.sleep(1000);

    } catch (Exception e) {

    }

}

输出：

private static final Object[] EMPTY_ELEMENTDATA = {};

和

private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};

两个居然一模一样

查看一下注释

/**

 * Shared empty array instance used for default sized empty instances. We

 * distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when

 * first element is added.

 */

中文翻译：

还是不太明了

接着往下看:

remove方法:

public boolean remove(Object o) {

    if (o == null) {

        for (int index = 0; index < size; index++)

            if (elementData[index] == null) {

            	//仅仅移除第一个对象

                fastRemove(index);

                return true;

            }

    } else {

        for (int index = 0; index < size; index++)

            if (o.equals(elementData[index])) {

                //仅仅移除第一个对象

                fastRemove(index);

                return true;

            }

    }

    return false;

}

fastRemove方法：

private void fastRemove(int index) {

    modCount++;

    int numMoved = size - index - 1;

    if (numMoved > 0)

        System.arraycopy(elementData, index+1, elementData, index,

                         numMoved);

    elementData[--size] = null; // clear to let GC do its work

}

grow方法

    private void grow(int minCapacity) {

        // overflow-conscious code

        int oldCapacity = elementData.length;

        int newCapacity = oldCapacity + (oldCapacity >> 1);

        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);

    }

去除空闲的区域

public void trimToSize() {

    modCount++;

    if (size < elementData.length) {

        elementData = (size == 0)

          ? EMPTY_ELEMENTDATA

          : Arrays.copyOf(elementData, size);

    }

}