正文
java之ArrayList.add
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ArrayList添加
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
elementData[size++] = e ：e为传入的需要存储的元素，elementData 是ArrayList中存放元素的数组缓存区，当ArrayList初始化时长度为0，当存放第一个元素时，长度为10
/**
* The array buffer into which the elements of the ArrayList are stored.
* The capacity of the ArrayList is the length of this array buffer. Any
* empty ArrayList with elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA
* will be expanded to DEFAULT_CAPACITY when the first element is added.
*/
transient Object[] elementData; // non-private to simplify nested class access
ensureCapacityInternal(size + 1) :size为ArrayList的长度，表示当前集合中的元素数量
private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}
private static int calculateCapacity(Object[] elementData, int minCapacity) {
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
return Math.max(DEFAULT_CAPACITY, minCapacity);
}
return minCapacity;
}
minCapacity：表示最小容量，calculateCapacity（）方法中逻辑：如果向集合中添加元素时elementData为长度为零的数组，则设置为初始容量为DEFAULT_CAPACITY=10
private void ensureExplicitCapacity(int minCapacity) {
modCount++;
// overflow-conscious code
if (minCapacity - elementData.length > 0)
grow(minCapacity);
}
modCount：修改次数，判断使用最小容量减去当前数组的长度是否大于零，如果大于零则表示需要扩容，反之当前容量不需要扩容
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
int newCapacity = oldCapacity + (oldCapacity >> 1);
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);
}
grow()为扩容方法，传入当前容量值，获取当前数组缓存区的长度，根据当前缓冲区长度进行计算扩容，扩容的数量是当前缓存区长度的1.5倍。最后使用Arrays.copyOf方法进行数组扩容
