CODEWITHSUNDEEP
javaobjectlinked-list
user3753722
user3753722

Reputation: 163

How to make linked list function return specific class object instead of "Object" in Java?

I'm new to java. unvisited and visited are linked lists with elements that are Node class objects, how can I make this method return a Node class object instead of an "Object"? I need to be able to use the output from this function to move onto the next unvisited puzzle state but I can't access the puzzle state within the Node class, and if I try to make the function return a Node it says it's a type mismatch (even though every single element in the list is a Node...). Please help, thank you. 

/**
 * Removes last visited puzzle state from unvisited queue and adds it to the visited list. 
 * Returns next puzzle state to visit from unvisited queue. 
 */
public Object nextState() {
    // if unvisited is empty, return null (no solution)
    if (unvisited.size() == 0) { 
        return null;
    }
    // remove visited node from unvisited list & add to beginning of visited list
    visited.addFirst(unvisited.removeFirst());
    // visit next unvisited node
    Object first = unvisited.getFirst();
    return first;
}

Upvotes: 0

Views: 941

Answers (2)

pratim_b
pratim_b

Reputation: 1210

public Node nextState() {
// if unvisited is empty, return null (no solution)
    if (unvisited.size() == 0) { 
        return null;
    }
    // remove visited node from unvisited list & add to beginning of visited list
    visited.addFirst(unvisited.removeFirst());
    // visit next unvisited node
    Object first = unvisited.getFirst();
    if(first instance of Node){
        return (Node) first;
    }
    return null;
}

The problem is your unvisited.getFirst() is returning an object of type Object. So you need to cast it to Node type and return it. 'instance of' is a preventive measure, you can avoid it if you think it always returns an objet of type Node

Upvotes: 0

06needhamt
06needhamt

Reputation: 1605

change the return type of the function to Node instead of object like so

public Node nextState() {
// if unvisited is empty, return null (no solution)
    if (unvisited.size() == 0) { 
        return null;
    }
    // remove visited node from unvisited list & add to beginning of visited list
    visited.addFirst(unvisited.removeFirst());
    // visit next unvisited node
    Node first = unvisited.getFirst();
    return first;

Upvotes: 1

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