package xin.rtime.collections.list;import java.util.Arrays;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.NoSuchElementException;// 模拟ArrayList的实现
public class ArrayList<E> {private transient int modCount = 0;    // 修改次数private transient Object[] elementData; // 数据集合private static final Object[] EMPTY_ELEMENTDATA = {}; // 默认空数组private int size; // 数组实际个数private static final int DEFAULT_CAPACITY = 10; // 默认长度private static final int MAX_ARRAY_SIZE = Integer.MAX_VALUE - 8;  // 数组最大长度// 默认构造函数public ArrayList() {elementData = EMPTY_ELEMENTDATA; // 默认等于空集合
    }// 初始化指定长度public ArrayList(int initialCapacity) {if (initialCapacity < 0) // 长度小于0 抛异常throw new IllegalArgumentException("Illegal Capacity: " + initialCapacity);this.elementData = new Object[initialCapacity]; // new一个指定长度的对象数组
    }// 添加元素public boolean add(E e) {ensureCapacityInternal(size + 1);elementData[size++] = e; // 放置添加的元素return true;}// 删除元素public boolean remove(E e) {if (e == null) {for (int index = 0; index < size; index++)if (elementData[index] == null) {  // 删除 null
                    fastRemove(index);return true;}} else {for (int index = 0; index < size; index++)if (e.equals(elementData[index])) {   // eqals比较
                    fastRemove(index);return true;}}return false;}private void fastRemove(int index) {modCount++;int numMoved = size - index - 1;      // 当前size - index - 1    数组从0开始if (numMoved > 0)System.arraycopy(elementData, index+1, elementData, index,numMoved);   // system arraycopyelementData[--size] = null; // clear to let GC do its work   gc回收
    }public E remove(int index) {rangeCheck(index);modCount++;E oldValue = elementData(index);int numMoved = size - index - 1;if (numMoved > 0)System.arraycopy(elementData, index+1, elementData, index,numMoved);elementData[--size] = null; // clear to let GC do its workreturn oldValue;}// 获取元素public E get(int index) {rangeCheck(index);   // index校验return elementData(index);}@SuppressWarnings("unchecked")E elementData(int index) {return (E) elementData[index];}private void rangeCheck(int index) {if (index >= size)throw new IndexOutOfBoundsException(outOfBoundsMsg(index));}private String outOfBoundsMsg(int index) {return "Index: "+index+", Size: "+size;}// 返回元素个数public int size() {return size;}// 判断当前容量是否能否装下元素private void ensureCapacityInternal(int minCapacity) {if (elementData == EMPTY_ELEMENTDATA) // 空集合minCapacity = Math.max(DEFAULT_CAPACITY, minCapacity); // 10 传入的
ensureExplicitCapacity(minCapacity);}// 提供外部遍历public Iterator<E> iterator() {return new Itr();}private class Itr implements Iterator<E> {int cursor;       // index of next element to return    游标int lastRet = -1; // index of last element returned; -1 if no such    最后元素下标int expectedModCount = modCount;  // 当前数组修改次数public boolean hasNext() {return cursor != size;  // 当前游标是否等于size
        }@SuppressWarnings("unchecked")public E next() {checkForComodification();   // 检查数组是否被操作过int i = cursor;if (i >= size)throw new NoSuchElementException();Object[] elementData = ArrayList.this.elementData;if (i >= elementData.length)throw new ConcurrentModificationException();cursor = i + 1;return (E) elementData[lastRet = i];}public void remove() {if (lastRet < 0)throw new IllegalStateException();checkForComodification();  // 检查集合是否被操作过try {ArrayList.this.remove(lastRet);cursor = lastRet;lastRet = -1;expectedModCount = modCount;} catch (IndexOutOfBoundsException ex) {throw new ConcurrentModificationException();}}final void checkForComodification() {if (modCount != expectedModCount)throw new ConcurrentModificationException();}}// 判断容量 扩容private void ensureExplicitCapacity(int minCapacity) {modCount++;  // 修改+1if (minCapacity - elementData.length > 0) // 当前长度 大于 数组长度
            grow(minCapacity);}public void add(int index, E element) {rangeCheckForAdd(index);ensureCapacityInternal(size + 1);  // Increments modCount!!System.arraycopy(elementData, index, elementData, index + 1,size - index);elementData[index] = element;size++;}private void rangeCheckForAdd(int index) {if (index > size || index < 0)   // index 超出 size  或者  index 小于0 ---> 数组越界throw new IndexOutOfBoundsException(outOfBoundsMsg(index));}public E set(int index, E element) {rangeCheck(index);   // 校验index是否满足
E oldValue = elementData(index);elementData[index] = element;return oldValue;}/**<<      :     左移运算符，num << 1,相当于num乘以2>>      :     右移运算符，num >> 1,相当于num除以2>>>    :     无符号右移，忽略符号位，空位都以0补齐*/// 扩容private void grow(int minCapacity) {int oldCapacity = elementData.length; // 当前数组长度int newCapacity = oldCapacity + (oldCapacity >> 1);  // 新容量大小 = 原来长度 + 原来长度 右移一位，除以2if (newCapacity - minCapacity < 0)  // 新长度 - 传的长度 小于  0newCapacity = minCapacity;   //
        if (newCapacity - MAX_ARRAY_SIZE > 0)  // 当前长度超出最大容量newCapacity = hugeCapacity(minCapacity);// minCapacity is usually close to size, so this is a win:elementData = Arrays.copyOf(elementData, newCapacity);   // 拷贝原来数据
    }// 判断容量private int hugeCapacity(int minCapacity) {if (minCapacity < 0) // overflowthrow new OutOfMemoryError();return (minCapacity > MAX_ARRAY_SIZE) ?Integer.MAX_VALUE :MAX_ARRAY_SIZE;}}