Agfdhyk

How to use the methods of a subclass of a superclass in another class in which I created a ArrayList?

I created a ArrayList of a superclass in another class. This superclass has three subclasses, each with their own methods. How do I use those methods?

And also, how can I use the instance variables of those subclasses?

Because you used the name of the superclass as your generic type, you are using the interface that the superclass provides in the ArrayList.

You can add subclass types to the list, but you cannot safely use unique methods introduced in the subclasses without first checking exactly which subclass the object is, then making a cast to the subclass.

Here is an example:

public class A {



    public void methodFromA() {

        System.out.println("From class A");

    }



}





public class B extends A {



    public void methodFromB() {

        System.out.println("From class B");

    }



}



public class C extends A {



    public void methodFromC() {

        System.out.println("From class C");

    }



}

and here are these classes in use, using an ArrayList with the superclass type:

public static void main(String args) {



    List<A> myList = new ArrayList<>();



    A object1 = new A();

    B object2 = new B();

    C object3 = new C();



    myList.add(object1);

    myList.add(object2);

    myList.add(object3);



    for (A object : myList) {

        object.methodFromA();



        if (object instanceof B) {

            B castedObject = (B) object;

            castedObject.methodFromB();

        }

        else if (object instanceof C) {

            C castedObject = (C) object;

            castedObject.methodFromC();

        }

    }

}

the resulting output:

From class A

From class A

From class B

From class A

From class C

As far as using instance variables, they should be accessed by public getters and setters, used after checking and casting, as demonstrated above.

First of all if you are not able to call super class method which will reflect to concrete subclass it means your design isn't good, you should thing it again.

But, anyway you can get item from arraylist and check it using instanceof like:

if (item instanceof FirstSubClass){

   FirstSubClass f = (FirstSubClass) item;

   f.methodInFirst();

} else if (...)

   .....