CODEWITHSUNDEEP
javagenericstree
SeekingAlpha
SeekingAlpha

Reputation: 7817

Cannot Resolve Method when using generics

I am trying to implment a tree for my project.

This tree will contain nodes which are different board states after some move.

Right now my project is structured like so:

                               src
            Agent      Support              Test               Threes
        Tree.java      Some class.java      some class          Board.java

I want my tree to store these Board objects kept in package src.Threes. However in my Tree class it is not letting me access my public board methods.

I am confident that I am just missing some really basic thing but I cannot figure this out after spending time hunting down what I am missing.

Please see my Tree.java code below:

package src.Agent;


import java.util.ArrayList;
import src.Threes.Board; // unused import
import java.util.List;


public class Tree<Board> {

    private Node<Board> root;

public Tree(Board RootData){
    root = new Node<Board>(RootData);
    //root.data = RootData;
    //root.children = new ArrayList<Node<Board>>(); // maximum length of 4


}





public static class Node<Board>{
    private Board data;
    private Node<Board> parent;
    private List<Node<Board>> children;

    public Node(Board board){
        data = board;
        children = new ArrayList<Node<Board>>();

    }

    private boolean addChild(Board board){
        return !board.gameOver(); // Cannot resolve method gameOver() (public method in Board).
    }




}

public static void main(String[] args){

}

}

Upvotes: 2

Views: 3931

Answers (1)

Jon Skeet
Jon Skeet

Reputation: 1502076

This is the problem:

public static class Node<Board>

That's declaring a generic class called Node, and Board is a type parameter. Within Node, the identifier Board refers to the type parameter called Board, not the type Board itself.

It looks like you don't really want it to be generic at all, so you can just change it to:

public static class Node {
    ...
}

Then change every time you use Node<Board> to just Node within the rest of the code.

Likewise, I suspect you don't want Tree to be generic.

If you do want Tree and Node to be generic, you should declare them like this:

public static class Node<T> {
    private T data;
    private Node<T> parent;
    private List<Node<T>> children;
    ...
}

... but then you can't refer to Board-specific members within Node. You could constrain T to be Board or a subtype:

public static class Node<T extends Board> {
    private T data;
    private Node<T> parent;
    private List<Node<T>> children;
    ...
}

... and at that point your gameOver etc calls will work - but that would be an odd mix of being Board-specific and generic at the same time. I wouldn't expect a Node or Tree class to have any concept of "game over". Separate your concerns!

Upvotes: 2

Related Questions