ArrayList的源码分析
/**
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- Default initial capacity.
- 初始化容量为10
*/
private static final int DEFAULT_CAPACITY = 10;
private static final Object[] 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 = {};
/**- 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
/** - The size of the ArrayList (the number of elements it contains).
@serial
*/
private int size;
//最大数组大小
private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;
//默认实例为一个空数组
public ArrayList() {
this.elementData = DEFAULTCAPACITY_EMPTY_ELEMENTDATA;
}
//添加元素
public boolean add(E e) {
//确定容量
ensureCapacityInternal(size + 1); // Increments modCount!!
elementData[size++] = e;
return true;
}private void ensureCapacityInternal(int minCapacity) {
ensureExplicitCapacity(calculateCapacity(elementData, minCapacity));
}private void ensureExplicitCapacity(int minCapacity) {
modCount++;// overflow-conscious code //超过扩容 if (minCapacity - elementData.length > 0) grow(minCapacity);
}
private void grow(int minCapacity) {
// overflow-conscious code
int oldCapacity = elementData.length;
//扩容方式 旧容量+旧容量右移一位
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);
}
//循环清除
public void clear() {
modCount++;// clear to let GC do its work for (int i = 0; i < size; i++) elementData[i] = null; size = 0;
}
//删除 --很巧妙的删除
public E remove(int index) {
rangeCheck(index);modCount++; E oldValue = elementData(index); //获得需要移动的位数 int numMoved = size - index - 1; if (numMoved > 0) //进行复制,最后一位会保留下来 System.arraycopy(elementData, index+1, elementData, index, numMoved); //数组大小减少一位,最后一位赋值为空 elementData[--size] = null; // clear to let GC do its work return oldValue;
}
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