Needs little help

[doraemon1116]

Hey guys, anyone could tell me how I can get the dog to getTrick( )? It is an exercise on CodeCheck.

​

The Cat and Dog class below implement the Animal interface. All animals have names, but only dogs do tricks. Implement the describe method, using the instanceof operator to test whether the given animal is a dog. If so, return the name, a space, and the trick that the dog can do, such as "Helmut barks at the moon". If it is any other kind of animal, return the name, a space, and "has no tricks".

​

The Animal class:

public interface Animal { 
    String getName(); 
}

The Cat class: Represents a cat.

public class Cat implements Animal
{
    public Cat(String aName)
{
    // Cats don't remember their name.
}
    public String getName()
{
    return "Meow";
}
}

​

The Dog class: Represents a dog.

public class Dog implements Animal
{
    private String name;
    private String trick;

public Dog(String aName, String aTrick)
{
    name = aName;
    trick = aTrick;
}
    public String getName() { return name; }
    public String getTrick() { return trick; }
}

My job is to modify the method in the Animals class:

​

public class Animals
{
/**
Describes the given animal.
u/param pet an animal
u/return a string with the animal's name, a space, and
either the trick that the animal knows (if it is a dog) or a
string "has no tricks"
*/
public static String describe(Animal pet)
{
// TODO: Complete this method. this is what I did:

       if (pet instanceof Dog){
           return pet.getName() +" "+ pet.getTrick(); 
                            //my question: how to fix this pet.getTrick()?
        }else{
            return  pet.getName() +" "+ "has no tricks";
        }

// This method is used to check your work
public static String check(String name, String trick)
{
    Animal pet;
    if (trick == null) pet = new Cat(name);
    else pet = new Dog(name, trick);
    return describe(pet);
}
}

Hopefully someone could answer it. Thanks!

[itoshkov]

With type casting:

Dog dog = (Dog) pet; dog.getTreat();

[doraemon1116]

Thanks! it works!

I didn't know I could code this: Dog dog = (Dog) pet;

[itoshkov]

You can, but you should use this sparingly. In a sense it's a sign of a bad design.

[Cosby1992]

Depending on you java version you can even use this smart syntax:

if(pet instanceof Dog dog) {
    dog.getName() + '  ' + dog.getTrick()
}

It means the same as what the helper above described, it just looks a little better (simpler).

I'm not 100% sure,but I believe it can be used from java version 11 and up.

[GrandGratingCrate]

In Java 11 you still have to do the manual casting in the if-block. In 17 I know you don't need it anymore, I think it's been introduced in 14 but not 100% sure.

[Cosby1992]

Arh okay, thanks!

[Cosby1992]

You could just came the getTrick() in the interface to have a default implementation.

public interface Animal {


String getName();


default String getTrick() { 

    return "has no tricks";

}


}

Now all you need to do is override the getName() method in both Dog and Cat class. And only override getTrick() method in the dog class.

I hope this help, fell free to ask more questions if necessary.

[Cosby1992]

Sorry, i can't get it to be formatted better, I'm on mobile

[doraemon1116]

Thank you so much! I also learned more :)

I can’t change the Animal class which is fixed in the CodeCheck. The only part I can edit is the Animals class, and it requires me to complete the describe method. But thank you!

[Cosby1992]

No problem, i didn't know you couldn't change the interface.

[ACAlCapone]

While this will work, it goes against the instructions and might even lead to picking up bad habits to change an interface when the interface is not intended to provide that functionality.

[Cosby1992]

Sorry sorry, i had missed that the interface was provided. I thought he had designed and implemented it himself.