Priority Queue cannot be applied to given types

Question

I am new with working with priority queues and have formatted this code wrong, and I want to have my priority be a straight line distance to a city however I don't beleive I passed this information to the queue correctly. Looking at the API I need to set the SLD as a the comparator

public PriorityQueue(int initialCapacity, Comparator comparator)

Creates a PriorityQueue with the specified initial capacity that orders its elements according to the specified comparator.

but this isn't clear to me.

public static void GreedySearchMap(map Romania) {
    boolean done = false;

    city current;

    int numsteps = 10;
    int cursteps;
    int choice;
    int numconnections;
    int totaldist;

    cursteps = 0;
    current = Romania.Arad;
    totaldist = 0;

    /*create queue*/
    PriorityQueue<city> q = new PriorityQueue<city>(city city,int SLD);         
    q.offer(current);
    current.visited = true;

    while (!done) {
        System.out.printf("Step %d, In %s, Distance\t%d\n", cursteps,
                current.getname(), totaldist);

        if (current.getname() == "Bucharest")
            done = true;
        else {

            current = q.poll();
            cursteps++;
            numconnections = current.getconnections();

            for (int i = 0; i < numconnections; i++) {
                choice = i;
                if (current.getcity(choice).visited == false) {
                    //totaldist += current.getdist(choice);
                    q.offer(current.getcity(choice), current.getSLD());
                    current.visited = true;
                }
            }
        }
    }

    System.out.printf("-----------------------\n");
}

My error is:

P:\csci395\hw4>javac GS.java
GS.java:85: error: method offer in class PriorityQueue<E> cannot be applied to g
iven types;
                                                            q.offer(current.
getcity(choice), current.getSLD());
                                                             ^
  required: city
  found: city,int
  reason: actual and formal argument lists differ in length
  where E is a type-variable:
    E extends Object declared in class PriorityQueue
 1 error

if (current.getname() == "Bucharest") Don't compare Strings with '=='. Use .equals() instead. Best practice is using it like this: "stringLiteral".equals(stringVariable) because you can avoid having a NullPointerException. — RaptorDotCpp
city city,int SLD is how parameters are declared, while new PriorityQueue<city>(city city,int SLD) is constructor invocation (not definition). It should be new PriorityQueue<city>(someInteger, anInstanceOfCaparator). The argurments someInteger, anInstanceOfCaparator must be of types as required by the constructor signature. — Bhesh Gurung

RaptorDotCpp RaptorDotCpp · Accepted Answer · 2013-04-15T19:23:42

First of all, give classes a capital name. 'city city' could generate compiler errors. Secondly, your error message tells you what is wrong.

You should give a Comparator to your PriorityQueue. An int is not even a class object, it's of a primitive type. Look up Java Comparators (java.lang.Comparator) for more information.

Priority Queue cannot be applied to given types

2 Answers