Question

Quick question i imagine, but i’m having trouble getting a clear answer from googling.

So i have 3 objects. Card, Deck, Player.
Both Deck and Player have an array of cards and both are declared in main.

Can i do the following in main() to get a reference to a card from deck into player?

player.getcard(deck.draw())

deck.draw() returns a Card and getcard is: player.getcard(Card card)

And yes, I’m coming from c++.

Answer 1

Short answer: yes, assuming that getcard actually puts its parameter into some private field in the Player class.

Long(er) answer: In Java, there are only two things available to you – primitives and references. The primitives are the numeric types, characters, and booleans. Everything else is an object, and all objects are references. So, when you write

Foo f = new Foo();

a new object of type Foo is created and on the (garbage-collected) heap, and a reference, which you can also think of as a “pointer,” is placed on the stack. The Java language gives you few real ways to examine that reference, though (you can’t cast it to a pointer or a long, for example) so you can just think of it as an opaque handle.

So, when you write

player.getcard(deck.draw())

the call

deck.draw()

returns a reference to an object of type Card, and that object is passed to the player.getcard method. Then, if the Player class looks something like

public class Player {
    private List<Card> cards;
    // ...
    public void getcard(Card card) {
        cards.add(card);
    }
}

then later calls to methods in Player that access the cards private field will see that the return value of deck.draw() has been added to cards.