简单复习一下ArrayList的扩容原理

    public boolean add(E e) {
        ensureCapacityInternal(size + 1);  // Increments modCount!!
        elementData[size++] = e;
        return true;
    }

    private void ensureCapacityInternal(int minCapacity) {
        if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
            minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
        }
 
        ensureExplicitCapacity(minCapacity);
    }

    private void ensureExplicitCapacity(int minCapacity) {
        modCount++;
 
        // overflow-conscious code
        if (minCapacity - elementData.length > 0)
            grow(minCapacity);
    }

    private void grow(int minCapacity) {
        int oldCapacity= this.elementData.length;
        int newCapacity= oldCapacity + (oldCapacity >> 1);
        if (newCapacity - minCapacity < 0) {
            newCapacity = minCapacity;
        }
 
        if (newCapacity - MAX_ARRAY_SIZE > 0) {
            newCapacity = hugeCapacity(minCapacity);
        }
 
        this.elementData = Arrays.copyOf(this.elementData, arg2);
    }