Type argument T is not within bounds of type-varia

问题:

This question already has an answer here:

• Java generics issue: Class “not within bounds of type-variable” error. 1 answer

I'm implementing a generic AVL tree but I'm having some compilation error.

My AVL Tee has to deal with Node<T> of type T.

In the example, the type is Event class.I want to compare the node.

But each type of data has to be compared differently, for that, i'm passing the comparison to the data itself to do the comparison.

I tried to make the Node implementing the Comparable Interface and the same thing to Event Class.

My code structure looks as follow:

The Tree Structure:

public class AvlTree<T extends Comparable<T>> {

private Node<T> root;

public AvlTree() {
    root = null;
}
 //other method to insert dellete operation in the tree

    }

The node Structure:

public class Node<T extends Comparable<T>> implements Comparable<T> {
        private T data;
        private Node<T> left;
        private Node<T> right;

        public Node() {
        }
         @Override
        public int compareTo(T t) {
          return this.data.compareTo(t);
        }
     }

The event Class that will be put in a node Object:

public class Event implements Comparable<Event>{
    private Point point;
    public Event() {
    }
    @Override
    public int compareTo(Event t) {
      return 1;
    }
    }

The code that gave me a compilation error is when i'm declaring an AvlTree :

private  AvlTree<Node<Event>> treeOfEvents;

Error:

type argument Node<Event> is not within bounds of type-variable T
where T is a type-variable:
T extends Comparable<T> declared in class AvlTree

回答1:

your Node has to implement Comparable like here:

public class Node<T extends Comparable<T>> implements Comparable<Node<T>> {

as your AvlTree expects something as generic Type which implements Comparable for exactly that type