使用泛型时无法解析方法

Question

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){

}

}

Answer 1

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!