Java Strings object in ArrayList

Question

In my MainActivity I have this lines of code:

    //data.getFirstUserInput()-1 is equal to user input.
     deck.setCardNumberEmpty(data.getFirstUserInput()-1);

       System.out.println("\n Cards on table");
                 ArrayList<Deck> deck= deck.getCards();
                  Collections.sort(cards);
                  for (Deckc: deck
           System.out.print((format("%10s","\033[F[ " + c.getOneSpecificNumber())+ " ]"));}

This prints out my random card numbers. But the problem is they are not numerically sorted,

Any idea what I can do?

Card Class

public class Card {

    private String cardLetter;
    private String cardNumber;
    private String nullValue;

    public Card(String cardLetter, String cardNumber, String nullValue){
        this.cardLetter = cardLetter;
        this.cardNumber = cardNumber;
        this.nullValue = nullValue;
    }

  public String getOneSpecificNumber() { return cardNumber;}
  public void setCardNumber(String x){  cardNumber = x;  }


private ArrayList<Deck> deck = new ArrayList();
public Deck(){
                   char A  = 'A';
    int repeats = 2, numOfCards = 8;
    for ( int i = 0; i<numOfCards;i++){
        for (int j = 0; j<repeats; j++){
            cards.add(new Card((char) ( A + i ) + "",i+1,""));
        }
    }
}

ninja.coder · Accepted Answer · 2016-03-27 13:41:09Z

5

In order to sort the cards Array as per the cardNumber your Card class has to implement the Comparable and override compareTo().

Here is the code snippet:

public class Card implements Comparable<Card> {

    private String cardLetter;
    private String cardNumber;
    private String nullValue;

    public Card(String cardLetter, String cardNumber, String nullValue){
        this.cardLetter = cardLetter;
        this.cardNumber = cardNumber;
        this.nullValue = nullValue;
    }

    public int compareTo(Card c) {
        if(StringUtils.isEmpty(this.cardNumber) || 
           StringUtils.isEmpty(c.cardNumber)) return -1;
        return Integer.parseInt(this.cardNumber) - Integer.parseInt(c.cardNumber);
    }

    public String getOneSpecificNumber() { return cardNumber; }

    public void setCardNumber(String x) {  cardNumber = x; }
}

StringUtils is part of Apache Commons Lang3, if you do not want to include it in your project then you can do something like this:

if(null == this.cardNumber || "".equals(this.cardNumber) ||
       null == c.cardNumber || "".equals(c.cardNumber)) return -1;

Now you just have to do this in order to sort:

Collections.sort(cards);

Example:

System.out.println("\n Cards on table");
List<Card> cards = deck.getCards();
Collections.sort(cards);
for (Card c: cards) {
    System.out.print((format("%10s","\033[F[ " + c.getOneSpecificNumber())+ " ]"));
}

edited Mar 27, 2016 at 13:41

answered Mar 27, 2016 at 13:09

ninja.coder

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12 Comments

user3506 Over a year ago

public int compareTo(Card c){ return this.cardNumber - c.cardNumber; } I'm not sure what this piece of code does, but It gives me an error. "Bad operand types for binary operator'-' first type: String second type: String

user3506 Over a year ago

Exception in thread "main" java.lang.NumberFormatException: For input string: "" Any idea why I could get this error? Tried ovveride the annotation but It's the same problem

ninja.coder Over a year ago

@user3506 You have null or blank values in cardNumber. Add a check to prevent exception. I have updated the answer using the StringUtils. Decide the return order appropriately in such cases.

user3506 Over a year ago

I guess your last updated answer is the check right? Or am I suppose to add an nullPointerException in order to prevent following error for the isEmpty method? "Cannot find symbol" "Symbol"method isEmpty(String)" "location class StringUtils"

ninja.coder Over a year ago

@user3506 Yes, the updated answer includes the check. If you want to use StringUtils then you'll have to include the Apache Commons Lang3 JAR: mvnrepository.com/artifact/org.apache.commons/commons-lang3/3.4 Alternatively you can do something like this: if(null == this.cardNumber || "".equals(this.cardNumber))

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