Type mismatch: cannot convert from Object to Class object

Question

How should I enqueue an object given that this object has several parameters and I need these parameters.

Eg:- BFS--> I need to enqueue and dequeue the current position but it gives me an error msg.

To be more specific :

                               /*Start = new Pos(i, j, 0);*/
public static int search(char[][] maze, Pos source) {
            MyQueue SP = new Queue();
            // pushes source to Q
            SP.enqueue(source);
            // marks source as visited
            visited[source.xPos][source.yPos] = true;
            // enters main loop - checks if Q is nonempty
            while (!SP.isEmpty()) {
                // gets next element off of queue
                Pos current = SP.dequeue(); //<< Here is the error "Type mismatch: cannot convert from Object to Pos"
                // gets neighbors of current
                ArrayList<Pos> neighbors = getNeighbors(maze, current);
                for (Pos neighbor : neighbors) {
                    // checks for exit
                    if (maze[neighbor.xPos][neighbor.yPos] == 'E') {
                        EX = neighbor.xPos;
                        EY = neighbor.yPos;
                        return neighbor.dist;
                    }
                            Q.enqueue(neighbor);
                }
            }
            // exit is not reachable
            return 0;
        }

Where Pos as follwoing :

public class Pos {
public int xPos, yPos, dist;

public Pos(int xPos, int yPos, int dist) {
    this.xPos = xPos;
    this.yPos = yPos;
    this.dist = dist;
}
}

For more illustration of my queue implementation :

public interface MyQueue {
    public void enqueue(Object item);
    public Object dequeue();
    public boolean isEmpty();
    public int size();
    public Object peek();
}

When I print dequeued elements , something like this appears "project.Pos@55f96302".

Finally, how "in general" could add an object of a class to linked list?

@SotiriosDelimanolis I am trying to keep track of all nodes visited and print them eg: while(!Parent.isEmpty()){ System.out.print(Parent.dequeue() + " "); } — user3672907
– user3672907, Commented May 25, 2014 at 3:19

Alexandre Santos · Accepted Answer · 2014-05-25 03:23:34Z

1

To enqueue, you add an object to the queue. This one object will hold all parameters you need to add.

To dequeue, simply do Pos current = SP.dequeue();

The error you are receiving it is because your queue holds Objects. You should make it to hold Pos objects.

public interface MyQueue {
    public void enqueue(Object item);
    public Object dequeue();
    public boolean isEmpty();
    public int size();
    public Object peek();
}

Take a look at the source code of java.util.AbstractQueue for an example of Queues.

To address your last question, the value "project.Pos@55f96302" is displayed because your object Pos doesn't have a toString() method, such as:

public class Pos {
    public int xPos, yPos, dist;

    public Pos(int xPos, int yPos, int dist) {
        this.xPos = xPos;
        this.yPos = yPos;
        this.dist = dist;
    }

    public String toString() {
        return "print here the values of xPos, yPos, and dist";
    }
}

answered May 25, 2014 at 3:23

Alexandre Santos

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3 Comments

user3672907 Over a year ago

Sorry for inconvenience , but how could I implement that method? public String toString() { return "print here the values of xPos, yPos, and dist"; } whenever I typed that it gives me an error .. Changes made successfully as you stated and no errors yet except one I am facing now.

user3672907 Over a year ago

Thanks .. Fixed it as stated , but now I just retreive xPos & yPos using "Integer.toString(arg0 , arg1)" what if I want to return dist also?

Alexandre Santos Over a year ago

return "xPos="+xPos+", yPos="+yPos+", dist="+dist;

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