我需要使用什么方法将生产者转换为生成者

Question

Assume I have a loop that produces items:

for (int i = 0; true; i++) {
    ComplexObject co = new ComplexObject(i);
    System.out.println(co);
}

The standard behaviour would be to print a description about the objects, but that does not make that much sense for a real application.

I wish to write a custom iterator (generator) now via which I can obtain the elements.

So I need to write the next() method in such a way that it will return one ComplexObject on every next() call, so it is like one step in a loop.

How would I go about doing that? What general mechanism would you advise me to use?

Keep in mind that I dumbed down the real issue to make it explainable, in reality it is of course not as easy as I have stated here and that is why I need to achieve the exact same mechanism that I have asked.

Regards.

ps. (small rant) What is this bleep about only being allowed to post 6 questions per 24-hour period?

Answer 1

For the example you've given above, you'd need to save some state each time an element was retrieved in order to know what sort of state the next element should have.

Here's an example which does precisely that. I have not tested this, but it should clearly demonstrate what I'm suggesting.

public class ComplexObjectIterator implements Iterator<ComplexObject>{
    //track start, so you can tell how many elements were retrieved if you want.
    private final int start;
    private final int end;
    private int position;

    public ComplexObjectIterator(int start, int end){
        if(start>end) throw new Exception("Start must be less "+
            "than or equal to end.");
        this.start = start;
        this.end = end;
        this.position = start;
    }

    public boolean hasNext(){
        return position < end;
    }

    public ComplexObject next(){
        if(position >= end) 
            throw new Exception("No more elements");
        ComplexObject obj = new Complexobject(this.position);
        position+=1;
        return obj;
    }

    public void remove(){
        if(position >= end)
            throw new Exception("No more elements");
        position+=1;
    }
}

If you truly want an endless iterator, this code can easily be changed to provide that kind of behavior.

Note that iterators are typically used to return elements from an underlying data structure. Because here you have no underlying structure, I'd create a new interface called Generator for your purposes to prevent confusing anyone looking at your code.

Far as the limit on questions, its probably there to prevent malicious users from attacking the site with an overload of questions. Not that you're doing that, just offering a possible explanation.