ArrayList源码解析
作者:互联网
ArrayList是List集合的一个实现类,它可以快速查询元素。ArrayList的查找时通过索引下标进行查找,所以ArrayList的查找快,当从ArrayList的中间位置插入或者删除元素时,需要对数组进行复制、移动、代价比较高。因此,它适合随机查找和遍历,不适合插入和删除。ArrayList线程不安全。
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
//当构建一个无参构造器时,ArrayList会默认构造一个长度为10且空的数组。
/**
* Default initial capacity.
*/
private static final int DEFAULT_CAPACITY = 10;
/**
* Constructs an empty list with an initial capacity of ten.
*/
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
/**
* Shared empty array instance used for default sized empty instances. We
* distinguish this from EMPTY_ELEMENTDATA to know how much to inflate when
* first element is added.
*/
private static final Object[] DEFAULTCAPACITY_EMPTY_ELEMENTDATA = {};
public boolean add(E e) {
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}
private void ensureCapacityInternal(int minCapacity) {
// elementData和DEFAULTCAPACITY_EMPTY_ELEMENTDATA默认为空数组
if (elementData == DEFAULTCAPACITY_EMPTY_ELEMENTDATA) {
// DEFAULT_CAPACITY和 minCapacity做比较,把大的数字赋值给minCapacity,由于是第一次添加元素所以返回默认的容量大小,它为10
minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity);
}
ensureExplicitCapacity(minCapacity);
}
private void ensureExplicitCapacity(int minCapacity) {
modCount++;//当前对象操作次数
// overflow-conscious code
if (minCapacity - elementData.length > 0)//当前元素长度为零
grow(minCapacity);//扩容
}
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;//将当前元素长度赋值给oldCapacity
int newCapacity = oldCapacity + (oldCapacity >> 1);// newCapacity的值是oldCapacity的1.5倍
if (newCapacity - minCapacity < 0)//第一次添加元素newCapacity为0
newCapacity = minCapacity;// newCapacity为10
// private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
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);//给元素进行扩容,如果是第一次添加元素需要将elementData的容量扩容到10,才能进行添加元素
}
private static int hugeCapacity(int minCapacity) {
if (minCapacity < 0) // overflow
throw new OutOfMemoryError();
return (minCapacity > MAX_ARRAY_SIZE) ?
Integer.MAX_VALUE :
MAX_ARRAY_SIZE;
}
标签:int,ArrayList,elementData,newCapacity,private,minCapacity,解析,源码 来源: https://blog.csdn.net/weixin_42206497/article/details/115728175