CODEWITHSUNDEEP
java
user69514
user69514

Reputation: 27629

Remove element from linked list JAVA

OK here is my problem. I have a linked list of card objects.

I have the following method

  public void removeCard(Card card){
        cards.remove(card);

  }

if I create Card c = new Card(5,C); for example

and there is a card with the exact same values 2, and C in the linked list (cards).

If I call the method CardPile.remove(card)
I dont get any errors, but the element that's equal to the parameter card is not removed. Any ideas why this is not happening?

import java.util.LinkedList;

public class CardPile {

    final char [] suit = {'C','D','H','S'};
    final char [] rank = {'A','2','3','4','5','6','7','8','9','T','J','Q','K'};

    LinkedList<Card> cards;


    public CardPile(){
            cards = new LinkedList<Card>();
    }


    public void addCard(Card card){
            cards.addLast(card);
    }
    public void removeCard(Card card){
            cards.remove(card);

    }
    public void removeSpecial(Card card){
            LinkedList<Card> temp = new LinkedList<Card>();
            for(int i=0; i<cards.size(); i++){
                    if(cards.get(i).equals(card)){
                            temp.add(cards.get(i));

                    }
            }
            cards = temp;
    }

    public void listCards(){
            for(int i=0; i<cards.size(); i++){
                    System.out.print(cards.get(i).toString()+" ");
            }
            System.out.println();
    }

    public boolean isEmpty(){
            if(cards.size()==0)
                    return true;
            else
                    return false;
    }

    public Card drawCard(){
            return cards.removeLast();
    }

    public boolean hasCard(Card card){
            int index = 0;
            boolean contained = false;
            if(cards.size()==0){
                    System.out.println("error, cards size is 0");
                    return false;
            }
            else{
                    while(index<cards.size() && !contained){
                            if(cards.get(index).isEqual(card)){
                                    System.out.println("Card found");
                                    contained=true;
                            }
                            index++;
                    }
            }

            return contained;
    }
}

Upvotes: 1

Views: 6733

Answers (4)

michaelliu
michaelliu

Reputation: 1697

Has your Card class implemented equals and hashCode methods? Whenever logic equality is desired other than identity equality (i.e. two references point to the same object), programmer should override these two methods. The default implementation in java.lang.Object does only identity equality check.

Upvotes: 0

Journeyman Programmer
Journeyman Programmer

Reputation: 1366

I bet the Card class doesn't override equals() and hashcode() method.

The default implementation by Object class simply checks "==", i.e. if two variables point to the same object instance. You need to override equals() and hashcode() to provide proper equal-ness check. See excellent discussion on the topic here - http://java.sun.com/developer/Books/effectivejava/Chapter3.pdf

With proper equals() and hashcode(), your code can be further simplied. For example, the hasCard() method can simply call List method contains().

Upvotes: 8

sandro
sandro

Reputation: 11

chances are the equals method in the card class is using just a '==' operator. Make sure that comparisons are being done so that two objects with identical face/suit values are considered equal.

Upvotes: 1

starblue
starblue

Reputation: 56752

Probably they are not equal then.

Check the equals() method on Card.

Upvotes: 1

Related Questions