1、查看ArrayList的add方法,場景假設,一個list長度是10,目前有5個元素
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
size是目前的元素個數等於5。ensureCapacityInternal(size + 1)進行判斷是否有增加1個元素的空間。
2、進行判斷,目前minCapacity=6.elementData是此時的數組。
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);
}
如果增加元素後的數組長度比數組長度大,就進行擴容。
3、擴容原來數組長度的1.5倍,創建新的數組,把原來的數組數據copy到新的數組裏面。
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);
}