Java: Implementing Comparable Issue

Question

I'm new here and was looking for some advise on my code. I'm trying to make it possible for an arrayList ArrayList<patient> heartPatientArray = new ArrayList<patient>(); //heart patients ArrayList<patient> heartPatientArray = new ArrayList<patient>(); //heart patients to be able to be sorted on a patient's arrivalTime .

Code:

    class patient implements Comparable
{
    int typeSickness; //1 for heart 2 for gastro 3 for bleeding
    double arrivalTime; //what time they arrived   SORT BY
    int deathTime; // what time they are set to balk or die
    int status; //0 for being cared for, 1 to n for location in line, -1 if dead
    int personalNumberInLine; //personal number in line updated everytime someone enters the line
    double timeSpentInQueue; //total time before they either died or were able to be treated
    int idOfPerson; //unique id the person gets when entering the queue
    boolean isAlive;

    public patient(int sickness, double arrival, int ID) { //sets the patients sickness, time arrived, and ID
        typeSickness=sickness;
        arrivalTime=arrival;
        idOfPerson = ID;
    }
    public int getTypeSickness() {
        return typeSickness;
    }
    public void setTypeSickness(int typeSickness) {
        this.typeSickness = typeSickness;
    }
    public double getArrivalTime() {
        return arrivalTime;
    }
    public void setArrivalTime(double arrivalTime) {
        this.arrivalTime = arrivalTime;
    }
    public int getDeathTime() {
        return deathTime;
    }
    public void setDeathTime(int deathTime) {
        this.deathTime = deathTime;
    }

    public int getStatus() {
        return status;
    }
    public void setStatus(int status) {
        this.status = status;
    }
    public int getNumberInLine() {
        return personalNumberInLine;
    }
    public void setNumberInLine(int numberInLine) {
        this.personalNumberInLine = numberInLine;
    }
    @Override
    public int compareTo(patient one) {
        if (this.getArrivalTime() < one.getArrivalTime()) {
            return -1;
        }
        else if(this.getArrivalTime() > one.getArrivalTime()){
            return 1;
        }

        return 0;
    }

some code edited out for time's sake

I've tried styling it after some code I found online but I'm getting an error on compareTo(patient one) of Remove Override Notation, and an error on class patient implements Comparable telling me I must make the class abstract.

After I implement the compareTo correctly, how would I go about sorting the heartPatientArray ?

Answer 1

You are implementing the raw form of the Comparable interface. Because of this, compareTo takes an Object , which explains why you are getting an error attempting to implement the interface.

Instead, pass your class as the type parameter.

class patient implements Comparable<patient>

Then your compareTo method, as is, will implement Comparable<patient> properly.

Typically, Java naming conventions would say to capitalize your class name.

class Patient implements Comparable<Patient>

You can sort your list with:

Collections.sort(heartPatientArray);

If you'd like to sort it in reverse order, you can specify that with:

Collections.sort(heartPatientArray, Comparator.reverseOrder());

In general, you can sort it however you want by passing an instance of Comparator<Patient> , implementing Comparator 's compare method, taking care to pass a type parameter to Comparable like we are now doing for Comparable . Then pass an instance of Comparator<Patient> as the second argument to Collections.sort .

Answer 2

Replace

class patient implements Comparable

with

class patient implements Comparable<patient>

otherwise you need to implement compareTo(Object o) in your class.

When you have instances of a Comparable class, you can just add them to an ArrayList and use the method Collections.sort .

Answer 3

So, basically what you want is to be able to compare between 2 patient objects. The way it is now, you are being able to compare between a patient and some other object. To ensure, that you are only comparing patient objects, you would need to change

class patient implements Comparable

to

class patient implements Comparable<patient>

The way you have down already is not wrong in any way (except for the compareTo param). You can, of course, compare a patient to some other object. If you wish to pursue that way,

@Override
public int compareTo(Object obj) {
    // you would want to see if the `Object` is of `patient` type
    if( !(obj instanceof patient) )
        return -1;    // `obj` IS NOT OF TYPE `patient`; PICK YOUR RETURN VALUE; IDEALLY THROW AN EXCEPTION
    patient one = (patient) o;
    if (this.getArrivalTime() < one.getArrivalTime()) {
        return -1;
    }
    else if(this.getArrivalTime() > one.getArrivalTime()){
        return 1;
    }

    return 0;
}

Then, you can sort it by calling Collections.sort(..) or something.