1.Itr 类的概述

Itr 类是 Iterator 接口的内部类，它实现了 Iterator 接口，并且提供了一种迭代访问集合中元素的方法。它的构造函数需要一个 Collection 类型的参数，而且只能在 Iterator 接口中调用，不能在外部类中调用。

2.Itr 类的实现

Itr 类实现了 Iterator 接口，它提供了 hasNext() 和 next() 方法，用于访问集合中的元素。hasNext() 方法用于检测集合中是否还有元素，next() 方法用于获取下一个元素。此外，Itr 类还实现了 remove() 方法，用于删除集合中的元素。

3.Itr 类的代码实现

123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112
public class Itr implements Iterator<E> {
    int cursor;       // index of next element to return
    int lastRet = -1; // index of last element returned; -1 if no such
    int expectedModCount = modCount;
    final ArrayList<E> list;
    
    Itr(ArrayList<E> list) {
        this.list = list;
    }
    public boolean hasNext() {
        return cursor != size;
    }
    @SuppressWarnings("unchecked")
    public E next() {
        checkForComodification();
        int i = cursor;
        if (i >= size)
            throw new NoSuchElementException();
        Object[] elementData = list.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();
        try {
            list.remove(lastRet);
            cursor = lastRet;
            lastRet = -1;
            expectedModCount = list.modCount;
        } catch (IndexOutOfBoundsException ex) {
            throw new ConcurrentModificationException();
        }
    }
    final void checkForComodification() {
        if (list.modCount != expectedModCount)
            throw new ConcurrentModificationException();
    }
}
Java