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My assignment is to create a simple Appointment superclass with three ( Daily, OneTime , Monthly) subclasses.

then I need to ask user to enter different appointments and store them in an ArrayList through a method called add. user should select the type of the appointment too.

I am new to polymorphism and try to find a polymorphic solution instead of using instanceof Operator.

Is it possible in my case?

Could you help me to have a better understanding of polymorphism please?

femchi
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    For what exactly do you need `instanceof`? It is generally a not so good idea to use `instanceof`. If you tell us a little bit more about what you are trying to check, we can help you. – Turing85 Jun 30 '15 at 19:57

4 Answers4

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You could start with the Java Tutorial here: https://docs.oracle.com/javase/tutorial/java/IandI/polymorphism.html

Kevin Hooke
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You won't need the instanceof operator at all. Make an Appointment class and make each time (Daily, OneTime, Monthly) extend appointment so they can use it's variables and methods.

Example:

public Daily extends Appointment

From there you should be able to make a main class to test what you've made and store the values in an ArrayList. For example:

List<Appointment> arrayList = new ArrayList<Appointment>();
arrayList.add("supply subclass object that you've created here");

Continue to add until all subclasses have been added to your appointment arraylist. Hope this helps.

unsensibled
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If you only need to store/add all the subtypes in an ArrayList , then you can choose the type parameter (the Class type within '<' and '>') as the superclass ie Appointment. So you can do List<Appointment> apps = new ArrayList<Appointment>();

now you can store all the subtypes as follows :-

apps.add(new Daily()); apps.add(new OneTime()); apps.add(new Monthly());

If you want to get any object from this ArrayList you can also assign it in a refrence variable of parent type ie Appointment as Appointment a = apps.get(0);

And finally if you want to call any overriden method on this a variable it will automatically call the overriden method of the actual subtype, by the property of Polymorphism.

Also if you want to somewhere specifically check the class of Appointment reference variable you can use getClass() method and compare it with the subclaases. So i am not sure why & where you want to use instanceof. Hope this might clear your queries a bit.

AnkeyNigam
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Actually, it would be even better if you use interfaces. Interface specifies contract (i.e. what should the class be and what should it be able to do), and helps to avoid problems related to inheritance e.g. dependency on superclass methods. And still lets you inherit other classes. Overall - interfaces are more flexible.

I would code:

public Daily implements Appointment

and then just as @unsensibled mentioned:

List<Appointment> arrayList = new ArrayList<>();
Appointment daily = new Daily();
arrayList.add(daily);
Piotrek Hryciuk
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