*Arraylist源码分析：*

*DEFAULT_CAPACITY*** = 10；默认容量大小 ，如果没有向集合中添加任何元素的时候，集合的容量是0.添加一个元素之后，容量就变成10了。

Object[] *elementData* *存放元素的数组*

*Size* *集合的大小*

*Add() 添加操作*

*下面是比较重要的源码*

public boolean add(E e) {
    ensureCapacityInternal(size + 1);  // Increments modCount!!  size=0
    elementData[size++] = e;
    return true;
}
private void ensureCapacityInternal(int minCapacity) { //现在 minCapacity=1 
    ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
private void ensureExplicitCapacity(int minCapacity) {
    modCount++;

    // overflow-conscious code
    if (minCapacity - elementData.length > 0)//1-0>0 条件成立
        grow(minCapacity);
}
private void grow(int minCapacity) {
    // overflow-conscious code
    int oldCapacity = elementData.length;
    int newCapacity = oldCapacity + (oldCapacity >> 1);//0
    if (newCapacity - minCapacity < 0)
        newCapacity = minCapacity;//newCapacity =1
    if (newCapacity - MAX_ARRAY_SIZE > 0) 1-(Integer.MAX_VALUE - 8;)>0不成立
        newCapacity = hugeCapacity(minCapacity);
    // minCapacity is usually close to size, so this is a win:
    elementData = Arrays.copyOf(elementData, newCapacity);//赋值elementData 数组长度为1
}

*结论：ArrayList每次进行扩容都是原来的1.5倍。视频讲解https://www.bilibili.com/video/BV1zD4y1Q7Fw?p=12*