ArrayList源码学习（1.1）

public class ArrayList<E> {
    //默认容量
    private static final int DEFAULT_CAPACITY = 10;
    //初始化数组
    private static final Object[] EMPTY_ELEMENTDATA = {};
    //初始化存储数组
    transient Object[] elementData;
    //包含的元素个数
    private int size;

    //无参构造 空集合
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

    //有参构造 根据参数初始化大小    
    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);
        }
    }

    //去掉集合中的空元素
     public void trimToSize() {
        modCount++;
        //如果集合的大小小于它存储实体数组的长度，就按照集合的大小截取数组非空部分。
        //类似于字符串的去空格
        if (size < elementData.length) {
            elementData = (size == 0)
              ? EMPTY_ELEMENTDATA
              : Arrays.copyOf(elementData, size);
        }
    }

    //增加元素
     public boolean add(E e) {
        //需要的最小容量为当前元素个数+1，调用确认内部容量方法。
        ensureCapacityInternal(size + 1); 
        elementData[size++] = e;
        return true;
    }

    //内部确认需要的容量private
     private void ensureCapacityInternal(int minCapacity) {
         //如果当前数组还没有元素存在，就用默认大小来初始化数组
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }

        ensureExplicitCapacity(minCapacity);
    }
    //确认具体容量数值
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        //内存溢出考量代码
        //如果最小需要的size大于数组当前长度的话，就继续grow
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

    private void grow(int minCapacity) {
        // overflow-conscious code
        //数组的旧长度
        int oldCapacity = elementData.length;
        //新长度为1.5倍旧长度
        int newCapacity = oldCapacity + (oldCapacity >> 1);

        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        //按照需要创建新数组
        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 ://list最大容量依然是Integer.MAX_VALUE 
            MAX_ARRAY_SIZE; 
    }


}