Help with comparing generic types

post solved

I am no expert in things like this, far from it, but shouldn't the object held by your list implement the Comparable interface? I think that you declare this something like so:

Code:

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public class OrderedList<E extends Comparable<E>> implements List<E>, Iterable<E> {
  //....

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(I used List here rather than ListInterface since I have no idea what ListInterface is).

Yes, but for this project I was given the test program and was told not to change it. implementing the Comparable interface causes an error in the test program.

Bound mismatch: The type T is not a valid substitute for the bounded parameter <E extends Comparable<E>> of the type OrderedList<E>

I think that I have solved the problem. But now I can't get my add method to work. Here is what I am using:

Code:

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when I run the program it adds the first item to the list then it gives me the following error:

Exception in thread "main" java.lang.NullPointerException
at java.lang.Character.compareTo(Unknown Source)
at TestOrderedList$1.compare(TestOrderedList.java:24)
at TestOrderedList$1.compare(TestOrderedList.java:1)
at OrderedList.add(OrderedList.java:34)
at TestOrderedList.test0(TestOrderedList.java:30)
at TestOrderedList.main(TestOrderedList.java:7)

Incorrect code:

Code:

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                for (int i = 0; add == true;i++)
                        if (compare(newEntry,list[i])>=0){
                                list[size] = newEntry;
                                add = true;}
                       
                        size++;
               
                return true;

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1. add is ALWAYS true, it never changes to false.
2. list[size] = newEntry;. YOu should to insert new element in ith position.