ArrayList源碼學習（1.1）

public class ArrayList<E> {
    //默認容量
    private static final int DEFAULT_CAPACITY = 10;
    //初始化數組
    private static final Object[] EMPTY_ELEMENTDATA = {};
    //初始化存儲數組
    transient Object[] elementData;
    //包含的元素個數
    private int size;

    //無參構造 空集合
    public ArrayList() {
        this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
    }

    //有參構造 根據參數初始化大小    
    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++;
        //如果集合的大小小於它存儲實體數組的長度，就按照集合的大小截取數組非空部分。
        //類似於字符串的去空格
        if (size < elementData.length) {
            elementData = (size == 0)
              ? EMPTY_ELEMENTDATA
              : Arrays.copyOf(elementData, size);
        }
    }

    //增加元素
     public boolean add(E e) {
        //需要的最小容量爲當前元素個數+1，調用確認內部容量方法。
        ensureCapacityInternal(size + 1); 
        elementData[size++] = e;
        return true;
    }

    //內部確認需要的容量private
     private void ensureCapacityInternal(int minCapacity) {
         //如果當前數組還沒有元素存在，就用默認大小來初始化數組
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }

        ensureExplicitCapacity(minCapacity);
    }
    //確認具體容量數值
    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;

        // overflow-conscious code
        //內存溢出考量代碼
        //如果最小需要的size大於數組當前長度的話，就繼續grow
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

    private void grow(int minCapacity) {
        // overflow-conscious code
        //數組的舊長度
        int oldCapacity = elementData.length;
        //新長度爲1.5倍舊長度
        int newCapacity = oldCapacity + (oldCapacity >> 1);

        if (newCapacity - minCapacity < 0)
            newCapacity = minCapacity;
        if (newCapacity - MAX_ARRAY_SIZE > 0)
            newCapacity = hugeCapacity(minCapacity);
        //按照需要創建新數組
        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; 
    }


}