用Java命名对象和继承

Question

I am learning Java and like to do it through examples. This is about inheritance and variables.

Animal.java

package inheritance; 
public class Animal {
    String name;

    public Animal (){
        System.out.println("A new animal has been created!");
    }

    public Animal (String name){
        System.out.println(name + " has been created!");
    }

    public void sleep() {
        System.out.println ("An animal sleeps...");
    }

    public void speak(){
        System.out.println("An animal *speaks*");
    }

    public void eat() {
        System.out.println ("An animal eats...");
    }

}

Dog.java

package inheritance;

public class Dog extends Animal {

    public Dog(){
        super();
    }

    public Dog(String name){
        super();
        System.out.println(name + " has been created!");
    }

    public void sleep(){
        System.out.println("A dog sleeps...");
    }

    public void speak(){
        System.out.println("A dog *barks*");
    }

    public void speak(String name){
        System.out.println(name + " *barks*");
    }

    public void eat() {
        System.out.println("A dog eats...");
    }

}

Zoo.java

package inheritance;

import java.util.ArrayList;
import java.util.List;

public class Zoo {

    public static void main(String[] args)
    {
        Dog ruffruff = new Dog();
        Dog Fido = new Dog("Fido");

        System.out.println();

        List<Animal> Animals = new ArrayList<Animal>();
        Animals.add(ruffruff);
        Animals.add(Fido);

        for (Animal AnAnimal:Animals) //for each structure.
        {
            AnAnimal.speak();
            AnAnimal.sleep();
        }
        Fido.speak("Fido");
    }
}

Output:

A new animal has been created!

A new animal has been created!

Fido has been created!

A dog barks

A dog sleeps...

A dog barks

A dog sleeps...

Fido barks

Desired Output:

A new animal has been created!

Fido has been created!

A dog barks

A dog sleeps...

Fido barks

Fido sleeps...

Questions:

How can I name a dog ONCE. So I want to name Fido ONCE in this code. Also I know I can say: Fido.speak("Fido"); But that messes up the array. Also seems illogical.

Why Array?

I have several others Cow, Bird, etc. I want a generic print out and then a name set to the object when I desire a name to be added.

Thanks for reading and your time! :)

------------------------------After Patricia's tips-----------------------------

package inheritance;

public class Animal {
    protected String name = "";

    public Animal (){
        System.out.println("A new animal is born!");
    }

    public Animal (String name){
        this.name = name;
        System.out.println("A " + name + " is born!");
    }

    public void sleep() {
        if (name.isEmpty())
        {
            System.out.println("An animal sleeps...");
        }
        else
        {
        System.out.println ("A " + name + " sleeps...");
        }
    }

    public void speak() {
        if (name.isEmpty())
        {
            System.out.println("An animal speaks...");
        }
        else
        {
        System.out.println ("A " + name + " speaks...");
        }
    }

    public void eat() {
        if (name.isEmpty())
        {
            System.out.println("An animal eats...");
        }
        else
        {
        System.out.println ("A " + name + " eats...");
        }
    }
}

Answer 1

I would change one of your constructors:

public Dog(String name){
    super();
    System.out.println(name + " has been created!");
}

to

public Dog(String name){
    super(name);
    System.out.println(name + " has been created!");
}

so that the Animal has a name, and then use the name in the message.