在Java中的两个类之间共享对象

Question

How do I share an object between two similar classes? For example,I would like to have two players in a game: Human and Computer They will be sharing a Deck class which has a variable : ArrayList cardList The human and computer object needs to access the cardList at the same time to draw cards during the gameplay.

The cardList arraylist is passed to either the Human or Computer as an argument in the constructor to add cards to their own hand ArrayList.Is it possible to return the changed cardList arraylist after I have taken some cards to add to hand arraylist?

Sorry if my explanation was confusing

Answer 1

ArrayList is a mutable container. If you pass it to both objects on construction, any mutation that occurs on it will be reflected at any other reference. Basically what I'm saying is: Pass the ArrayList to both Objects, make changes in either object and the changes will be available in the other object and vise-versa.

https://docs.oracle.com/javase/8/docs/api/java/util/ArrayList.html

Answer 2

This is already the case. If you have three classes Human, Computer and Deck.

Human :

public class Human {
    private Deck commonDeck;
    private card currentCard;

    public Human(Deck deck) {
        commonDeck = deck;
    }

    public pickCard() {
        currentCard = commonDeck.removeLastCard();
    }
}

Computer:

public class Computer {
    private Deck commonDeck;
    private card currentCard;

    public Computer(Deck deck) {
        commonDeck = deck;
    }

    public pickCard() {
        currentCard = commonDeck.removeLastCard();
    }
}

Deck:

public class Deck {
    private List<Card> cards;

    public Deck(){
        cards = new ArrayList<Card>();
        /*populate the list*/
    }

    public Card removeLastCard() {
        return cards.remove(cards.size() - 1);
    }
}

Then when in your main you do :

public static void main() {
    Deck deck = new Deck();
    Human human = new Human(deck);
    Computer computer = new Computer(deck);
    //human and computer share the same deck object

    human.pickCard(); //human will remove a card from the list deck.cards
    //The deck object in computer is the same as in human
    //So coputer will see that a card has been removed
}

As explained in the code comments, human and computer objects share the same deck object. They share the same reference to an instance of Deck. So whatever you do to deck in human, will be seen in computer.