How ArrayList increase 2017-07-14 05:46
As we all know ArrayList use array to store the items. The length of array is fixed. When the array can't hold all items it will increase. I want to know how ArrayList increases the length. I found the source code(JDK1.8) like following.
/**
* Increases the capacity to ensure that it can hold at least the
* number of elements specified by the minimum capacity argument.
*
* @param minCapacity the desired minimum capacity
*/
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);
}
The "minCapacity" is the min length which can hold all items. When we add an item into the ArrayList which length is 10. The "minCapacity" is 10 + 1 = 11. oldCapacity >> 1 means to get the half of the length. So the logic is when the space is not enough the space will increase 0.5 times.