Calling a recursive method from another class that reverses a linked list

Question

I have currently have 2 classes, Images and ImageNode. Inside the ImageNode class I have a recursive method that reverses the linked list. I believe my code is correct for that method, however i'm confused as to how I should be calling this method inside my Images class.

ImageNode method ---

 public ImageNode reverseUsingPrevious(ImageNode previous) {
    if(previous == null) return previous;

    ImageNode next = previous.getNext();

    if(next == null) return previous;

    previous.setNext(null);
    ImageNode rev = reverseUsingPrevious(next);
    next.setNext(previous);
    return rev;
}

Images method ----

private void reverseRec() {
    cursor.reverseUsingPrevious(head);
//the cursor is the currently selected image(node), head is the start of the linked list
}

I'm not 100% sure what I should be parsing into reverseUsingPrevious method.

"I believe my code is correct" So what is your question? What does not work? — user1907906
– user1907906, Commented Sep 19, 2014 at 9:43
I believe my reverseUsingPrevious is correct but not my reverseRec() method... that method is causing the problem — Dan_ENZ
– Dan_ENZ, Commented Sep 19, 2014 at 9:45
Please specify: is it a double linked list? Please post the ImageNode's class attributes. Did your task explicitly demand a recursive methods as solution? — SME_Dev
– SME_Dev, Commented Sep 19, 2014 at 9:47
You need to put a lot more info in this question. I'd suggest you remove all the stuff about images and nodes etc.. and think about what, fundametally, you are having problems with and ask that question. I wont vote you down since you are new, but you are asking for it. — HellishHeat
– HellishHeat, Commented Sep 19, 2014 at 10:13
My apologies, I will re-evaluate my problem and try explain it a bit better. Thanks — Dan_ENZ
– Dan_ENZ, Commented Sep 19, 2014 at 10:15

Lone nebula · Accepted Answer · 2014-09-19 10:43:14Z

1

Update the head by adding head = before the cursor.reverseUsingPrevious(head);.

Extra tip:

Even though the method reverseUsingPrevious probably works as it is, it doesn't call any methods or variables on the local object at all (apart from the call to reverseUsingPrevious), so it could just as well have been static.

But rather than making it static, you could drop the parameter (ImageNode previous), and replace every instance of previous with this.

Now, instead of calling reverseUsingPrevious(node), you put the node in front instead: node.reverseUsingPrevious().

answered Sep 19, 2014 at 10:43

Lone nebula

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1 Comment

Dan_ENZ Over a year ago

Thanks, I knew I was close, thanks for understanding what I was trying to get across. I do believe it could be better but It does the job I need it to do... Thanks for the tip, will keep that in mind.

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