ArrayList add方法

ArrayList

DEFAULT_CAPACITY 默认大小：10
add()添加元素

public boolean add(E e) {
     
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }
    
private static int calculateCapacity(Object[] elementData, int minCapacity) {
     
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
     
            return Math.max(DEFAULT_CAPACITY, minCapacity);
        }
        return minCapacity;
    }
    
private void ensureCapacityInternal(int minCapacity) {
     
        ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
    }

private void ensureExplicitCapacity(int minCapacity) {
     
        modCount++;

        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity); // 容量不够时进行扩容
    }


private void grow(int minCapacity) {
     
        // overflow-conscious code
        int oldCapacity = elementData.length;
        int newCapacity = oldCapacity + (oldCapacity >> 1);// 每次扩容1.5倍
        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);
    }