CODEWITHSUNDEEP
javagenerics
learningtocode
learningtocode

Reputation: 765

compareTo(K) in java.lang.Comparable<K> cannot be applied to (java.lang.Comparable)

I am trying to define a generic class which can work with any data type with Comparable interface defined.

The error message is compareTo(Key) in java.lang.Comparable<Key> cannot be applied to (java.lang.Comparable) on line 22

I suspect this has to do with my TreeNode class declaration, but I cannot figure out what it is.

Warnings [unchecked] unchecked call to TreeNode(Key) as a member of the raw type findLargestKElementsInTree.TreeNode on line 16

    class findLargestKElementsInTree<Key extends Comparable<Key>>{
      TreeNode root;

      int count=1;

      public void insert(Key k)
      {
       this.insert(k,root,root);

      }
      private void insert(Key k, TreeNode node,TreeNode parent)
      {
        if(this.root==null)
         root=new TreeNode(k);
        if(node==null)
        {
          node=new TreeNode(k);
          if(parent != null)
          {
           if(k.compareTo(parent.data)<0)
             parent.left=node;
           else
             parent.right=node;
          }
        }
        else
        {
          if(node.data.compareTo(k)>0)
             insert(k,node.left,node);
          else if(node.data.compareTo(k)<0)
             insert(k,node.right,node);
          else
            return;
        }
      }



      public void printK(int k)
      {
        postOrderK(root,k);
      }
      /*
       *       42
       *    40
       * 20    25
       *    10
       *      5
       * 
       * 
       * 
       * */
      public void postOrderK(TreeNode n,int k)
      {
       if(n==null) 
         return;
       if(n.right!=null)
         postOrderK(n.right,k);
       if(count <= k)
       {
         System.out.println(count+" largest number "+n.data);
         count++;
       }
       postOrderK(n.left,k);


      }

       public class TreeNode<Key extends Comparable<Key>>{
         Key data;
         TreeNode left;
         TreeNode right;
         TreeNode(Key d)
         {
           this.data=d;
           this.left=null;
           this.right=null;
         }
       }

       public static void main(String[] args)
       {
         findLargestKElementsInTree<Integer> tree=new findLargestKElementsInTree<Integer>();
         tree.insert(20);
         tree.insert(40);
         tree.insert(10);
         tree.insert(5);
         tree.insert(42);
         tree.insert(25);
         tree.printK(7);

       }

     }

I have looked at other questions on stack overflow which seem to be helping out with similar problem, but the solution suggested is to have a generic class, I think I already have that.

Thanks in advance!

Upvotes: 0

Views: 2574

Answers (2)

Marko Topolnik
Marko Topolnik

Reputation: 200168

Look at your method's signature:

private void insert(Key k, TreeNode node, TreeNode parent) {

Your node and parent parameters have the raw TreeNode type, but TreeNode is a generic class. Fix it by parameterizing as appropriate:

private void insert(Key k, TreeNode<Key> node, TreeNode<Key> parent) {

Same for the root, left, and right instance variables.

Upvotes: 4

Eran
Eran

Reputation: 393836

I think what you are missing is declaring the root instance to use the generic type TreeNode<Key> instead of the raw type TreeNode: 

class findLargestKElementsInTree<Key extends Comparable<Key>>{
  TreeNode<Key> root;
  ...

You should probably replace every place that has the raw type TreeNode with TreeNode<Key>.

Upvotes: 1

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