Overriding function with exact same content causes error

The title may be a bit misleading but I was not sure how to word this.

I have 2 classes, BinarySearchTree and HashTreeSet.

I am currently using HashTreeSet to implement a variant of BinarySearchTree using different sorts, compares and such.

Info:

• BinarySearchTree is fully functional
• HashTreeSet extends BinarySearchTree
• Both classes contains at the bottom a Node-class which represents each node in the tree

I have one problem and one problem only so far: HashTreeSet complains about my find(T target) function, saying the return-type Node<T> is incompatible with BinarySearchTree<T>.find(T).

BinarySearchTree implements the method find(T target).

I wanted to change some of the find-code in the HashTreeSet class, so I copied the function over, but now it complains about some return-statement.

I'll post parts of the code to avoid clutter, let me know if you want the full versions:

HashTreeSet

public class HashTreeSet<T extends Comparable<T>> extends BinarySearchTree<T> implements SimpleSet<T> {
  /*
   * Other functions
   */


  The error is highlighted here, see error message below
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           V 
  public Node<T> find(T target) {
    Node<T> current = findAgain(target, root);

    if( current == null )
      return null;

    return current;
  }
  private Node<T> findAgain(T target, Node<T> next){
    // Stuff
  } 
  class Node<T extends Comparable<T>> {
    // Stuff
  }
}

BinarySearchTree

public class BinarySearchTree<T extends Comparable<T>> implements SimpleSet<T> {

  /*
   * Other functions
   */
  public Node<T> find(T target) {
    Node<T> current = findAgain(target, root);

    if( current == null )
      return null;

    return current;
  }
  private Node<T> findAgain(T target, Node<T> next){
    // Stuff
  } 
  class Node<T extends Comparable<T>> {
    // Stuff
  }
}

Error

The return type is incompatible with BinarySearchTree.find(T)

When I attempt to QuickFix it, it changes the return-statement from Node<T> to treestuff.Node<T> but it still remain red and uncompilable. treestuff is the package in which both of these files are contained.