ArrayList
Last updated
Last updated
public boolean add(E e) {
// 确保数组容量足够大
ensureCapacityInternal(size + 1);
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)
// 扩容
grow(minCapacity);
}private void grow(int minCapacity) {
// 获去老数组的容量
int oldCapacity = elementData.length;
// 扩容,容量增加一半
// oldCapacity >> 1,相当于除以2
int newCapacity = oldCapacity + (oldCapacity >> 1);
if (newCapacity - minCapacity < 0)
newCapacity = minCapacity;
if (newCapacity - MAX_ARRAY_SIZE > 0)
newCapacity = hugeCapacity(minCapacity);
// copy到新数组
elementData = Arrays.copyOf(elementData, newCapacity);
}public void add(int index, E element) {
// 校验index是否超出数组容量
rangeCheckForAdd(index);
// 确保数组容量足够大
ensureCapacityInternal(size + 1);
// 将index后的元素整体后移一位
System.arraycopy(elementData, index, elementData, index + 1,
size - index);
elementData[index] = element;
size++;
}/**
* System类的静态native方法
* 实现数组之间的复制
* @param src 源数组
* @param srcPos 源数组要复制的起始位置
* @param dest 目标数组
* @param destPos 目标数组放置的起始位置
* @param length 复制的长度
*/
public static native void arraycopy(Object src, int srcPos,
Object dest, int destPos,
int length);