OOP-Java。 从主将Animal对象添加到Class中的Arraylist中

Question

Adding a second Animal, resets the animals Arraylist to index 0. So it holds the last entered animal. I also putted the UML design below, so it might be more understandable what I'm trying.

public class Cage {
    private int placeNr;
    private ArrayList<Animal> animals = new ArrayList<Animal>();

    public Cage(int place) {
        this.placeNr = place;
    }

    public int getCageNr() {
        return this.placeNr;
    }


    public void putAnimal(Animal animal) throws DuplicateNameException {
        if(!duplicatedAnimal(animal.getName())) {
            animals.add(animal);
        }
    }
}

At this point I'm confused. How do I add an Animal class in the an Arraylist located in Cage and stack my Animals in it.

private static void addAnimal() {
    Animal newAnimal;
    Cage cage;
    try {
        System.out.println("Name: ");
        String name = sc.next();
        System.out.println("Type: ");
        String type = sc.next();
        System.out.println("birthYear: ");
        int birthYear = sc.nextInt();
        System.out.println("Cage number: ");
        int cageNumber = sc.nextInt();

        cage = new Cage(cageNumber);
        newAnimal = new Animal(name, type, birthYear);
        cage.putAnimal(newAnimal);
    } catch (DuplicateNameException dne) {
        dne.getMessage();
    } catch (InputMismatchException ime) {
        System.out.println("Wrong input");
    }
}

If someone can push me in the right direction it will be awesome thanks!

UML: enter image description here

Answer 1

Every time you call addAnimal you will create a new Cage object and add the new animal to that cage. To add several animals to the same cage the addAnimal method can not be static and cage needs to be a member of some class (AnimalKeeper?)

Something like this

public class AnimalKeeper {
  private Cage cage;

  public Cage getCage() {
      return cage;
  }

  public addAnimalToCage(Animal animal) {
      //the same method as above minus the user input
      //which needs to be done somewhere else
  }
}

Answer 2

I tried my best to figure out what you meant exactly, refactor your code to smth like this

class DuplicateNameException extends Exception {

    private String message;

    public DuplicateNameException(String message){
        this.message = message;
    }

    public String getMessage(){
        return this.message;
    }

}

class Animal {
    private String name;

    public Animal(String name) {
        this.name = name;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}


class Cage {
    private int placeNr;

    private ArrayList<Animal> animals = new ArrayList<Animal>();

    public Cage(int place) {
        this.placeNr = place;
    }

    public int getCageNr() {
        return this.placeNr;
    }


    public void putAnimal(Animal animal) throws DuplicateNameException {
        if(!duplicatedAnimal(animal.getName())) {
            animals.add(animal);
        } else {
            throw new DuplicateNameException(animal.getName());
        }
    }

    private boolean duplicatedAnimal(String name) {
        for (Animal animal : animals)
            if (animal.getName().equals(name))
                return true;

        return false;
    }

    public static void main(String[] args) {
        Animal newAnimal;
        Cage cage;
        try {
            cage = new Cage(1);
            newAnimal = new Animal("Dog");
            cage.putAnimal(newAnimal);
            cage.putAnimal(new Animal("not dog"));
            cage.putAnimal(new Animal("Dog"));
        } catch (DuplicateNameException dne) {
            System.out.println(dne.getMessage());
        }
    }
} 

Note: with this code you need to consider cases with animals name written in lower case and upper case ( equals will return false in this case) use toLowerCase() or toUpperCase() to normelize the name to common ground

another option you can take is to use HashMap object, this structure type has duplication elimination build in, you will have to override the hashCode() function of Animal so the map will know how to hash each object, like

@Override
public int hashCode() {
  return this.name.hashCode()
}