ArrayList中迭代器(Iterator)源码解析

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package java.util;
import java.util.function.Consumer;
public interface Iterator<E> {
boolean hasNext();
E next();
default void remove() {
throw new UnsupportedOperationException("remove");
}
default void forEachRemaining(Consumer<? super E> action) {
Objects.requireNonNull(action);
while (hasNext())
action.accept(next());
}
}

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private class Itr implements Iterator<E> {
int cursor;
// 下一个元素的索引位置
int lastRet = -1; // 上一个元素索引的位置
//modCount用于记录ArrayList集合的修改次数,赋、值给expectedModCount 用于checkForComodification()方法判断ArrayList在迭代过程中是否发生修改
int expectedModCount = modCount;
Itr() {}	//无参构造方法
//通过判断curso的值和size是否相等来判断集合中是否还有可供访问的元素
public boolean hasNext() {
return cursor != size;
}
public E next() {
checkForComodification(); //判断集合的修改次数是否合法
int i = cursor; //记录索引位置
if (i >= size)
throw new NoSuchElementException(); //如果获取元素大于集合元素个数，则抛出异常
Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length)
throw new ConcurrentModificationException();
cursor = i + 1; //cursor + 1
return (E) elementData[lastRet = i]; //lastRet + 1 且返回cursor处元素
}
public void remove() {
if (lastRet < 0)
throw new IllegalStateException();
checkForComodification();
try {
ArrayList.this.remove(lastRet);//调用ArrayList的remove方法
cursor = lastRet;	//将上一次索引赋值给下一次索引，即cursor位置前移
lastRet = -1;	//重置lastRet
expectedModCount = modCount;//将ArrayList的modCount赋值给expectedModCount 这样就不会报错
} catch (IndexOutOfBoundsException ex) {
throw new ConcurrentModificationException();
}
}
//函数式接口实现
public void forEachRemaining(Consumer<? super E> consumer) {
Objects.requireNonNull(consumer);
final int size = ArrayList.this.size;
int i = cursor;
if (i >= size) {
return;
}
final Object[] elementData = ArrayList.this.elementData;
if (i >= elementData.length) {
throw new ConcurrentModificationException();
}
while (i != size && modCount == expectedModCount) {
consumer.accept((E) elementData[i++]);
}
cursor = i;
lastRet = i - 1;
checkForComodification();
}
//修改异常检查
final void checkForComodification() {
if (modCount != expectedModCount)//通过对比ArrayList的modCount值和Iterator的expectedModCount的值是否相等，来判断是否修改异常
throw new ConcurrentModificationException();
}
}