Java Community | Help. Code. Learn.•2w ago

java basics help

For this example:

public class Animal {
public void makeSound (){
   System.out.println("animal sounds");
   }
 }

public class Cat extends Animal{
public void makeSound (){
   System.out.println("meow");
   }
 }

public class Dog extends Animal{
public void makeSound (){
   System.out.println("woof");
   }
 }

public class test {
Animal dog = new Dog();
Animal cat = new Cat();
}

public class Animal {
public void makeSound (){
   System.out.println("animal sounds");
   }
 }

public class Cat extends Animal{
public void makeSound (){
   System.out.println("meow");
   }
 }

public class Dog extends Animal{
public void makeSound (){
   System.out.println("woof");
   }
 }

public class test {
Animal dog = new Dog();
Animal cat = new Cat();
}

I dont understand why we do this: Animal dog = new Dog(); Animal cat = new Cat(); Why not just do something like, Dog dog = new Dog();, Cat cat = new Cat(); Also why CAN we do this and why doesnt it throw an error, because ive seen it happen that the left hand side of the initialization was sometimes an interface? One thing that I found online was thit helps with abstraction, like for the method below. But why does it even make a difference at all, since Dog dog = new Dog(); is still an Animal so the method should it accept it too right? public void handleSound (Animal animal) { animal.makeSound(); }

13 Replies

JavaBot•2w ago

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ayylmao123xdd•2w ago

you can do both but most of the time its best to just do

Dog dog = new Dog()

Dog dog = new Dog()

and just like in the example at the bottom that you added passing an animal instead of a specific class like dog and cat means you can use this method for all animals

mjstxOP•2w ago

Ahh ok, so doing Animal dog = new Dog(); doesnt have any technical benefits, but just makes it clearer for the programmer/reader that dog implements/extends the Animal class. Is that right?

ayylmao123xdd•2w ago

basically yes however if you do animal dog then you only get the methods the animal has but for example if you got an extra method in the dog class then you wont be able to call it because you got an animal as reference so unless you know your method will receive different types of animal its best to use that specific type so dog cat etc search the strategy design pattern it can explain a lot

Kyo-chan•2w ago

Actually it is best to use the type that does the least, so that your program doesn't make any use of members that aren't needed, and stays free to replace one choice of class with another, without any change. I'm not sure what you think is the strategy pattern

ayylmao123xdd•2w ago

https://refactoring.guru/design-patterns/strategy/java/example

Strategy in Java / Design Patterns

Strategy pattern in Java. Full code example in Java with detailed comments and explanation. Strategy is a behavioral design pattern that turns a set of behaviors into objects and makes them interchangeable inside original context object.

ayylmao123xdd•2w ago

this here shows how casting to a different class can give you more methods if needed or way different ones but yes if its a generic method like changing animal name then if your animal class has a name field then theres no need to know what kind of a specific class it is like dog or cat

Kyo-chan•2w ago

.... That example shows no such thing. Design patterns usually do not cast anytjing in their typical examples.

ayylmao123xdd•2w ago

well if you need a specific method for like a dog or a cat you need to cast to that from the animal in the strategy but if you have a method for all animals then you dont need casting

Kyo-chan•2w ago

....... The point of strategy pattern is you don't need to do that. There would be no pattern if you did that, just ad hoc code.

ayylmao123xdd•2w ago

you do depending on the case want me to write an example

Divyanshu•2w ago

JavaBot•2w ago

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