如何根据对象的条件从java中的数组列表返回（和删除）对象

Question

For class I need to make a card game (bridge).

I have a Card class which defines all the attributes of a card, and a Deck class which generates the 52 cards. Also have a Hand class which randomly distributes cards from the deck to the four hands.

Now I need to make a method which takes as input a player's hand and the target suit, and returns the highest ranking card of that suit. I have:

private Card highestRankofSuit(ArrayList<Card> hand, char suit)
{
    ArrayList<Card> cardsOfSuit = null;
    for(int i = 0; i < hand.size(); i++)
    {
        if (hand.get(i).getSuit() == suit)
        {
            cardsOfSuit.add(hand.get(i));
        }
    }
    return cardsOfSuit(max(Card.getBridgeRank()));  //This is wrong because it only returns one int

}

What can I do to return the desired card? Also, I will also need to know how to remove a specific Card object from an ArrayList (based on info about the Card such as its rank and suit, but not knowing beforehand its position in the ArrayList).

First time posting here, thanks for all your help!

Answer 1

To return the relevant card you need to loop through all the cards from this suit and find the maximum one, as well as the index of this max card. Once you've checked all of them, return the card with the highest value. I think this is what you want (since you haven't provided all your code).

int max = -1;
int maxCardIndex = -1;
int i;
for(i = 0; i < cardsOfSuit.size(); i++) {
    int cardVal = cardsOfSuit.get(i).getBridgeRank();
    if( cardVal > max) {
       maxCardIndex = i;
    }
}
return cardsOfSuit.get(maxCardIndex);

For the removal of a card, just loop through all cards in the hand and check the details of the card, then remove it if your requirements are met. (You'll need to update this but it gives an example).

for(int i = 0; i < hand.size(); i++) {
    Card currentCard = hand.get(i);
    /* Check for what conditions you want to match in this if statement */
    if(currentCard.foo = "bar") {
       hand.remove(i);
    }
}

Answer 2

private Card highestRankofSuit(ArrayList<Card> hand, char suit){
  ArrayList<Card> cardsOfSuit = null;
  int maxIndex = 0;
  int maxCardNum = 0;

for(int i = 0; i < hand.size(); i++)// for loop1{
            if (hand.get(i).getSuit() == suit) {
                if(hand.get(i).getNumberOnCard() > maxCardNum){
                      maxIndex = i;
                      maxCardNum = hand.get(i).getNumberOnCard();
                }
            }
        }
return hand.get(maxIndex);

}

• Check if the card is of the correct suit
• Check if its number is higher than the current maximum number found
• if it is: save the index of the card in the hand ArrayList AND save the value of the number on the card so that if can be compared to the next card

Answer 3

The first alteration I would make is to use a for-each loop which iterates through the arraylist so you don't have to make so many get calls. We really need to see what the getBridgeRank() method does. Are you also using wanting to use the Math.max() method or your own max method?

private Card highestRankofSuit(ArrayList<Card> hand, char suit)
{
    ArrayList<Card> cardsOfSuit = null;
    for(Card c : habd)
    {
        if (c.getSuit() == suit)
            cardsOfSuit.add(c);
    }
    return cardsOfSuit(max(Card.getBridgeRank())); 
}

Answer 4

If you're using java 8, take a look at java.util.Stream

private Card highestRankofSuit(ArrayList<Card> hand, char suit) {
        Optional<Card> max = hand.stream().
                filter(card -> card.getSuit() == suit).
                max((o1, o2) -> Integer.compare(o1.getBridgeRank(), o2.getBridgeRank()));

        return max.orElse(null); //may return null
}

For removing the cards which match a condition (do not require java 8)

Iterator<Card> iterator = hand.iterator();
        while (iterator.hasNext()) {
            Card card =  iterator.next();
            //Change the following condition depending on your needs
            if(card.getSuit()=='I'){
                iterator.remove();
            }
        }

If you have already the Card that you want to remove you can just use ArrayList#remove(Object)

hand.remove(cardToRemove);