CODEWITHSUNDEEP
javagenericscompiler-errorsjava-8stack
Giacomo
Giacomo

Reputation: 571

Incompatible types initializing stacks of generic types in Java

I am trying to program a Stack structure on Java. My code looks as follows:

class Stack<T>{
  private static class Node<T>{
    private T data;
    private Node<T> next;

    public Node(T data){
      this.data = data;
    }
  }
  private Node<T> top;

  public Stack(){
    top = null;
  }
  public Stack(Node<T> top){
    this.top = top;
  }

  public static void main(String []args){
    Node<Integer> stackNode = new Node<Integer>(1);
    Stack<Node<Integer>> myStack = new Stack<Node<Integer>>(stackNode);
  }
}

in the main method, I first initialize a node called stackNode with the Integer 1, this works. What I then try to do, is initializing my Stack with the stackNode as top node. This is not working, when I compile I get the error:

    Stack.java:56: error: incompatible types: Node<Integer> cannot be converted to Node<Node<Integer>>
        Stack<Node<Integer>> myStack = new Stack<Node<Integer>>(stackNode);
Note: Some messages have been simplified; recompile with
    -Xdiags:verbose to get full output 1 error

Upvotes: 3

Views: 300

Answers (2)

azro
azro

Reputation: 54148

You use Stack<Node<Integer>> and Stack<T> which makes T=Node<Integer>, but in the constructor you have Node<T> so it would require a Node<Node<Integer>> and you give a Node<Integer>

You need to set same for both (and may use <> (diamond operator) for clarity) :

Node<Integer> stackNode = new Node<>(1);
Stack<Integer> myStack = new Stack<>(stackNode);

Upvotes: 3

Mureinik
Mureinik

Reputation: 311188

The Stack and the Node should have the same type:

Node<Integer> stackNode = new Node<Integer>(1);
Stack<Integer> myStack = new Stack<Integer>(stackNode);

BTW, using the <> syntax introduced in Java 7 could clean up the code a bit:

Node<Integer> stackNode = new Node<>(1);
Stack<Integer> myStack = new Stack<>(stackNode);

Upvotes: 5

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