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I'm running into some trouble with nested classes on a project for school. Currently, I'm trying to write a method to insert an item into a ragged array data structure. It uses an object created by a nested class to keep track of the 2d array location in order to get the indexes to insert at. However, I am getting the error "The method findEnd(E) is undefined for the type RaggedArrayList.ListLoc" on the line:

insertLoc.findEnd(item)

I have searched extensively both on stackoverflow as well as around the web and have not found the answer yet. If I have missed it and this is redundant (there are a lot of "method undefined for type questions", I know) then I apologize.

Here is the relevant code >>

nested class for ListLoc object:

private class ListLoc {
  public int level1Index;
  public int level2Index;

  public ListLoc() {}

  public ListLoc(int level1Index, int level2Index) {
     this.level1Index = level1Index;
     this.level2Index = level2Index;            
  }

  public int getLevel1Index() {
     return level1Index;
  }

  public int getLevel2Index() {
     return level2Index;
  }

  // since only used internally, can trust it is comparing 2 ListLoc's
  public boolean equals(Object otherObj) {
     return (this == otherObj);
  }
}

Method to find the last index of a matching item (not part of ListLoc nested class):

private ListLoc findEnd(E item){
  E itemAtIndex;

  for (int i = topArray.length -1; i >= 0; i--) {
     L2Array nextArray = (L2Array)topArray[i];

     if (nextArray == null) {
        continue;

     } else {

        for (int j = nextArray.items.length -1; j >= 0; j--) {
           itemAtIndex = nextArray.items[j];
           if (itemAtIndex.equals(item)) {
              return new ListLoc(i, j+1);
           }
        }
     }
  }

  return null;

}

Method attempting to add a new value to the ragged array:

boolean add(E item){
  ListLoc insertLoc = new ListLoc();
  insertLoc.findEnd(item);

  int index1 = insertLoc.getLevel1Index();
  int index2 = insertLoc.getLevel2Index();

  L2Array insertArray = (L2Array)topArray[index1];
  insertArray.items[index2] = item;

  return true;

}

Thanks for any input.

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3
  • Don't bother adding the homework tag anymore. :) We're not using it. I've already removed it for you. Commented Oct 8, 2012 at 17:51
  • 3
    Well at quick glance I would say it is because your method is private, or that the scope is wrong (the method is not in the correct location). You say that the method is not in ListLoc, but you are calling it like it is. Commented Oct 8, 2012 at 17:52
  • Didn't realize the homework tag wasn't used anymore. Sorry. Thanks for the feedback Commented Oct 8, 2012 at 18:06

4 Answers 4

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I'm going to bet that changing this:

ListLoc insertLoc = new ListLoc();
insertLoc.findEnd(item);

To this:

ListLoc insertLoc = findEnd(item);

Will fix your problem.

You're trying to call findEnd on the ListLoc class, but if you actually look at ListLoc, it's not defined there. When you tried to call findEnd on the insertLoc object, it fails because insertLoc is an instance of ListLoc, which we already said doesn't contain findEnd.

That being said, I'm going to bet that findItem is actually declared in the same class as the add method (let's just call it MyList), so you wanted to actually call MyList.findEnd, not the non-existent ListLoc.findEnd.

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2 Comments

Yup. That did it. Obviously, I'm still learning. Scope continues to be a challenge for me. I appreciate the help.
One way to think of it for this scenario is that the . accessor on objects help to define the scope. When you said insertLoc.findEnd, the . says, "look for non-static methods and fields in the class of insertLoc (the ListLoc class) and invoke or access them for the insertLoc object." For accessing methods and fields in the same class, remember that our call to findEnd is exactly the same as if we called this.findEnd (try it!), so it's also defining the scope. But here, the variable is this, and it ultimately gives us the class that defines add. Hope that helps :)
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You pretty much answered your own question.. You're trying to call findEnd on a ListLoc object, but ListLoc doesn't define a findEnd method. You need to either

a) Add an implementation for findLoc to ListLoc or

b) Call findLoc on the proper object (you haven't provided information about the other class so I can't say too much about it)

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Method to find the last index of a matching item (not part of ListLoc nested class):

Right - it's not part of ListLoc... but when you call it here:

ListLoc insertLoc = new ListLoc();
insertLoc.findEnd(item);

... you're trying to call it as if it is part of the class. It isn't, so you can't call it like that.

Either move it into ListLoc, or change the way you're calling the method.

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I am not sure if I am reading this correct, but from your explanation is looks like the findEnd method is defined outside of your class, therefore ListLoc indeed doesn't have a method by that name...

Where is your private ListLoc findEnd(E item) defined?

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