是否可以在Java中扩展迭代器的功能？ [英] Is it possible to extend the functionality of an iterator in Java?

问题描述

我想知道是否有办法扩展迭代器接口的功能。假设我们有一个实现Iterable接口的Class（在上面的例子中，我没有添加myFunction的Iterator接口的重写函数）。

I was wondering if there is a way to extend the functionality of the iterator interface. Suppose that we have a Class that implements the Iterable interface (in the example above, instead of the overridden functions of the Iterator interface I have added myFunction).

public class MyClass implements Iterable{

    @Override
    public Iterator iterator() {
        return new Iterator() {
            @Override
            public boolean hasNext() {
                throw new UnsupportedOperationException("Not supported yet.");
            }

            @Override
            public Tuple next() {
                throw new UnsupportedOperationException("Not supported yet.");
            }

            @Override
            public void remove() {
                throw new UnsupportedOperationException("Not supported yet.");
            }
            public void myFunction(){

            }
        };
    }
}

如果我将此代码放在另一个函数中，我会得到编译错误（找不到符号），我想知道为什么会发生这种情况。

If I put this code in another function I get compilation error ("cannot find symbol") and I was wondering why this happens.

public void anotherFunction(){
    MyClass a = new MyClass();
    a.iterator().myFunction();
}

推荐答案

是的，当然。您可以创建另一个界面：

Yes, of course. You could create another interface:

interface MyBetterIterator extends Iterator
{
    void myFunction();
}

然后让方法返回你的类型：

then make the method return your type:

public class MyClass implements Iterable{

    @Override
    public MyBetterIterator iterator() {
...
    }
}

此功能称为返回类型协方差，在Java 5。

The feature is called "return type covariance", introduced in Java 5.

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