CODEWITHSUNDEEP
javapolymorphism
pramiezequel
pramiezequel

Reputation: 41

Polymorphism 1 Superclass 4 Subclass

Let's says I have 5 classes, 1 superclass and 4 subclasses. My superclass is Animal and has Species and Charateristic, these 2 will be inherited to my subclasses.

4 subclasses are: Lion, Eagle, Bee, and Whale ( these 4 subclasses extend Animal ). These subclasses will have methods Voice() and Walk().

The question is, that my mentor told its student:

case 1. If this program is running it is launched, there will be a menu that shows that 4 subclasses / Animal objects.

case 2. After the user has chosen an animal, for example: Eagle. Then it shows what voice and movement an eagle has.

case 3. If the user chooses exit, then terminate the program.

In this case, we will use switch + case, right? But then my question is how do I call these 4 subclasses from my superclass?

If I add public static void main inside each of the subclasses, then these 4 subclasses become a main method, and I'm unable to set or create it with switch case. Or do I have to create another class that extends those 4 subclasses and call it?

Thank you, I hope you've understood what I mean :)

Upvotes: 0

Views: 121

Answers (2)

EmDroid
EmDroid

Reputation: 6066

You should access the subclass methods through virtual method calls (on a reference typed to the superclass). You can use Factory design pattern as well. Can be something like this:

int choice;
// read the choice, if exit chosen then exit

// getAnimal returns the actual animal instance
// (either a new instance or an existing one from internal registry)
// can select by switch() inside
Animal *animal = getAnimal(choice); // or Animal::getAnimal(choice), etc.

if (animal == null) {
    System.err.println("Invalid choice");
} else {
    // will call the methods on the actual specific animal retrieved by getAnimal()
    animal.Voice();
    animal.Walk();
}

Neither Animal nor the animal kinds should have main() - only the actual application which handles the entire logic (that could be the Animal class as well, but maybe better to create a separate class for the application itself).

EDIT: This is how the getAnimal() method could look like:

Animal * getAnimal(int choice)
{
    switch (choice)
    {
    case 1:
        return new Lion();
    case 2:
        return new Eagle();
    // etc.
    default:
        // invalid choice
        return null;
    }
}

Upvotes: 1

shnplr
shnplr

Reputation: 230

At some point you have to create your animal instances

Animal a1 = new Lion();
Animal a2 = new Eagle();
System.out.println(a1.Species());
System.out.println(a2.Species());

Create a separate class to control your program containing main e.g.

public class MyClass {
  public static void main(String[] args) {
    int opt = 1; // TODO - use args
    switch (opt) {
      case 1: 
        Lion obj = new Lion();
        System.out.println("Voice: " + obj.Voice() + ", Walk: " + obj.Walk();
        break;
      case 2:
        Eagle obj = new Eagle();
        System.out.println("Voice: " + obj.Voice() + ", Walk: " + obj.Walk();
        break;
 // etc
    }
  }
}

Upvotes: 1

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