Can't use abstract method

Question

I have an abstract class with abstract method "Action"

public abstract class BaseAnt {
    public BaseAnt(String name, int food, int water) {
        /.../
    }

    public abstract void action ();   
}

The class worker extends it:

   public class WorkerAnt extends BaseAnt {
    public WorkerAnt() {
        /.../
    }

    public void action() {
        AppStat.FOOD += mAge*0.1 + 10;
    }
}

And I'm trying to make loop

    public ArrayList<BaseAnt> antsArray;
        for (int i = 0; i < AppStat.antList.size(); i++) {
        if (AppStat.antList.get(i).getName() == "Worker") {
            AppStat.antList.get(i).action();
        }
    }

But I can't call the method action! How to fix it?

Error:

The method action() is undefined for the type BaseAnt

What do you mean with "I can't call"? Do you get a compilation error? Do you get an exception when running? Is the method simply not called? — isnot2bad, Nov 11 '13 at 16:48
You have made an error by writing `== "Worker"` when you should have `.equals("Worker")`. However, this is not the cause of your compiler error. — Kevin Panko, Nov 11 '13 at 17:04
for one, your comparison are flawed, which is what i was pointing at. as for the undefined method, the only explanation i see so far is that you are using a different BaseAnt class, and have a import issue. — njzk2, Nov 11 '13 at 17:06

ioreskovic · Answer 1 · 2013-11-11T17:11:13.257

Strings in Java are compared in this manner:

String foo = "foo";
String bar = "bar";
String foo2 = "foo";

foo.compareTo(bar); // false
foo.compareTo(foo2); // true

When you compare (foo == foo2), you're actually comparing references, which is a no-no, in your case.

Edit: I've just written a tiny test example:

import java.util.ArrayList;
import java.util.List;


public class BaseAntQuestion {

    public static void main(String[] args) {
        new BaseAntQuestion();
    }

    public BaseAntQuestion() {
        List<BaseAnt> ants = new ArrayList<>();

        for (int i = 0; i < 10; i++) {
            ants.add(new WorkerAnt());
        }

        for (BaseAnt ant : ants) {
            ant.action();
        }
    }

    public abstract class BaseAnt {
        public abstract void action();
    }

    public class WorkerAnt extends BaseAnt {

        @Override
        public void action() {
            System.out.println("Action!!!");
        }

    }

}

And it works just fine.

Can you please post the AppStat class? My gut is telling me you may have conflicing BaseAnt imports there.

Oh, thnx, but now problem in other. I cant call method action — Sunstrike, Nov 11 '13 at 16:50

score 0 · Answer 2 · answered Nov 11 '13 at 17:10

I think you are using and accessing your abstract class fine in the code you have posted.

I would suggest that the problem is somewhere in your AppStat class. In particular look at AppStat.antList and look to see if you may have accidentally created or referenced a different BaseAnt class.

As mentioned by others there is a problem with the way you are comparing strings, which you will want to look at, but that is not what is causing the error you are seeing.

Can't use abstract method

2 Answers2