How would I create a new object from a class using a for loop in java?

Question

I have a class named Card and I have this for loop:

int i;
for (i = 0; i < 13; i++) {
    Card cardNameHere = new Card();
}

What I want to do is create new instances based on the for loop. So for example, I would like the names to be card1, card2, card3, etc. The number would come from the for loop.

I have tried this and it does not seem to work:

int i;
for (i = 0; i < 13; i++) {
    Card card[i] = new Card();
}

Can anyone tell me what I am doing wrong?

Thanks.

So I am using the solution from Hovercraft Full Of Eels, but I have another problem.

I am using cardList.add(new Card()); , and when I try to use Card(i) to set the name, java won't let me do it. Using it without i works fine, but how do I access it so I can call another method on it such as setId. I would like to call cardName.setId();

The 2nd approach is going down the right path, but you want to declare an *Array of Cards*, say `Card[] cards = new Card[13]` outside the loop. Then you can assign each (new) card to the array, `cards[i] = new Card()` in the loop. — user2246674, Sep 30 '13 at 23:12
You seem to be trying to use variable variables. It's much better to use a collection and access each element by index. — George Brighton, Sep 30 '13 at 23:13

Hovercraft Full Of Eels · Accepted Answer · 2013-10-01T00:00:39.880

Create your array before the loop, and fill it inside the loop. Better to use an ArrayList though.

List<Card> cardList = new ArrayList<Card>();
for (i = 0; i < MAX_CARD; i++) {
  cardList.add(new Card());
  // or new Card(i) as the case may be
}

If you're filling a deck of cards, and you have your Suit and Rank enums nicely created, then:

List<Card> cardList = new ArrayList<Card>();
for (Suit suit: Suit.values()) {
  for (Rank rank: Rank.values()) { 
    cardList.add(new Card(suit, rank));
  }
}

Edit
You state in comment:

So I am using cardList.add(new Card()); , and when I try to use Card(i) to set the name, java won't let me do it. Using it without i works fine, but how do I access it so I can call another method on it such as setId. I would like to call the cardName.setId();

Card(i) doesn't make sense as you can't treat the Card class as if it were a method -- again I'm not even sure what to make of it, what you're trying to do here. If you need to extract a Card from the ArrayList, you will need to call the get(...) method on the ArrayList, here called cardList. Better still would be to set the Card properties in its constructor as I show in my 2nd code snippet.

Everyone has helped me so far, but this answer is closest to what I am working on. I already have an ArrayList but did not know that this could be done. Thank you. — jdc987, Sep 30 '13 at 23:15

score 5 · Answer 2 · answered Sep 30 '13 at 23:14

In Java, variable names have to be known at compile-time. Even in other languages like JavaScript, where that is not true, it is a good idea to not try to dynamically create variables at runtime.

This is exactly what arrays are meant to solve: when you have items of a known type, but unknown quanity at compile time. You need to declare the card as an array: Card[] cards

Card[] cards = new Card[13];
for (int i = 0; i < cards.length; i++) {
    cards[i] = new Card();
}

Notice I changed the for loop to loop through to cards.length, which is figured out at runtime, so that 13 does not have to be hard-coded in both places.

How would I create a new object from a class using a for loop in java?

2 Answers2

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