JDK源码阅读——ArrayList(2)

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public Iterator<E> iterator() {    return new Itr();}private 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;    public boolean hasNext() {        return cursor != size;    }    @SuppressWarnings("unchecked")    public E next() {        checkForComodification();        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();        try {            ArrayList.this.remove(lastRet);            cursor = lastRet;            lastRet = -1;            expectedModCount = modCount;        } catch (IndexOutOfBoundsException ex) {            throw new ConcurrentModificationException();        }    }    @Override    @SuppressWarnings("unchecked")    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++]);        }        // update once at end of iteration to reduce heap write traffic        cursor = i;        lastRet = i - 1;        checkForComodification();    }    final void checkForComodification() {        if (modCount != expectedModCount)            throw new ConcurrentModificationException();    }}

iterator()方法新建并返回一个ArrayList的迭代器，该迭代器是个内部类，扩展了Iterator< E >接口。迭代器分别使用两个int型变量cursor和lastRet分别指向下一个返回的元素和最近返回的元素。
迭代器中用得最多的方法是hasNext()和next()。hasNext()将cursor与ArrayList的size进行比较，若相等说明无下一个元素，则返回false，否则返回true；next()首先比较cursor与size，若cursor>=size则抛出异常，否则返回cursor所指向的元素并将cursor赋给lastRet，然后cursor++。
remove方法则删除lastRet所指向的元素，即上一个返回的元素，并将lastRet赋给cursor，同时lastRet = -1。

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