ArrayList源码学习

//默认的Arraylist
    private static final int DEFAULT_CAPACITY = 10;


    //一个空的数组
    private static final Object[] EMPTY_ELEMENTDATA = {};


    //默认初始化的空数组
    private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};


    //缓存数组
    transient Object[] elementData; 


    //list的目前容量
    private int size;
  
//最大容量
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//看的出来，ArrayList的基础还是数组。
//初始化
    public ArrayList(int initialCapacity) {
        if (initialCapacity > 0) {
    //指定容量的数组
            this.elementData = new Object[initialCapacity];
        } else if (initialCapacity == 0) {
   //默认一个空的数组
this.elementData = EMPTY_ELEMENTDATA;
        } else {
            throw new IllegalArgumentException("Illegal Capacity: "+
                                               initialCapacity);
        }
    }
    public ArrayList() {
    //一个空数组
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }
    public ArrayList(Collection<? extends E> c) {
        elementData = c.toArray();
        if ((size = elementData.length) != 0) {
            // 进行元素复制
            if (elementData.getClass() != Object[].class)
                elementData = Arrays.copyOf(elementData, size, Object[].class);
        } else {
            this.elementData = EMPTY_ELEMENTDATA;
        }
    }
  
//添加元素
    //添加元素
public boolean add(E e) {
ensureCapacityInternal(size + 1);  // Increments modCount!!
elementData[size++] = e;
return true;
}

    public void add(int index, E element) {
        rangeCheckForAdd(index);
        ensureCapacityInternal(size + 1);  // Increments modCount!!
//元素复制
        System.arraycopy(elementData, index, elementData, index + 1,size - index);
        elementData[index] = element;
        size++;
    }
  
//统计容量
private static int calculateCapacity(Object[] elementData, int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
   取默认容量和传入的容量的最大值
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }
  
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;
        //当前需要的容量大于现有容量就扩容
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }
private void grow(int minCapacity) {
        //原有的容量
        int oldCapacity = elementData.length;
//扩容为原来的两倍
        int newCapacity = oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0)
    //
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
    //容量有上界
            newCapacity = hugeCapacity(minCapacity);
        //元素拷贝
        elementData = Arrays.copyOf(elementData, newCapacity);
    }
//在查找元素的时候也是最简单的for循环
public int indexOf(Object o) {
        if (o == null) {
            for (int i = 0; i < size; i++)
                if (elementData[i]==null)
                    return i;
        } else {
            for (int i = 0; i < size; i++)
                if (o.equals(elementData[i]))
                    return i;
        }
        return -1;
    }
  
    //删除包含c的元素
public boolean removeAll(Collection<?> c) {
        Objects.requireNonNull(c);
        return batchRemove(c, false);
    }
//保留c中元素
public boolean retainAll(Collection<?> c) {
        Objects.requireNonNull(c);
        return batchRemove(c, true);
    }