Java 继承与泛型

Question

Can somebody explain (like for dummies) the following examples of inheritance in Java:

1) public class Dog <T extends Animal> {....
2) public class Buldog extends Dog<DogFood, DogCommands> {....
3) public class Buldog<T extends DogFood, K extends DogCommands> extends Animal implements LivingBeign, LivingThing<T,K> { ....

Answer 1

1) public class Dog <T extends Animal> {...

There will be an generic type In your Dog class which is inherit variables and methods from class (probably an abstract class Animal) This T must have and animal property.. For example assume you have a class Mammalian. We know that all mammalian are animal so they have what all animals have, and they can what all animals can.

So yo can call this as

public Dog<Mammalian> myDog = ...

There is a different situation.

2) public class Buldog extends Dog<DogFood, DogCommands> {....

So your dog class should be written like

/** T refers the food, and K refers commands*/
public class Dog<T,K> {....

So when you want to extend your class with Bulldog, you can leave generic or specify those generic types..

3) public class Buldog<T extends DogFood, K extends DogCommands> extends Animal implements LivingBeign, LivingThing<T,K> { ....

This is also as easy as above codes. The difference that you are desiring subclass of DogFood, which can be anyting, it can be Pap or Milk or Meat, and some subclass of DogCommands for example SitCommand, PlayCommand.. And as you are creating Buldog you know that It is Animal, so you don't want to write animal's property and methods again and since in Java you can't multiple inherit, you want also the other interfaces methods in your class..

I hope it is more understandable now.