Arraylist insights

[Jon Camilleri]

java.util
Class ArrayList<E>

1. This class is "unsynchronized" mean in the Java context?

Source: http://download.oracle.com/javase/6/docs/api.

2. "public int hashCode()

This method returns the hash code value for the object on which this method is invoked. This method returns the hash code value as an integer and is supported for the benefit of hashing based collection classes such as Hashtable, HashMap, HashSet etc. This method must be overridden in every class that overrides the equals method."

Why?
Does an ArrayList use hashCode() when processing?
How will my hashCode() algorithm affect the performance (memory use, efficiency of algorithms, CPU usage) of processing the ArrayList?

Source: http://www.technofundo.com/tech/java/equalhash.html.

3. I am not sure how to implement a hashCode() method for my Card class, which is extended by a Deck class.

package poker;
public class Card {

	public Card() {
		/*	null method */
	}
	public Card(Suit suit, Rank rank) {
        this.suit = suit;
        this.rank = rank;

    }

	public Card(short _suit, short _cardnumber)
	{
		switch (_suit) {
		case 1 :
			this.suit = Suit.CLUBS;
			break;
		case 2 :
			this.suit = Suit.DIAMONDS;
			break;
		case 3 :
			this.suit = Suit.HEARTS;
			break;
		case 4 :
			this.suit = Suit.SPADES;
			break;
		default :
			break;
		}

		switch (_cardnumber) {
		case 1 :
			this.rank = Rank.ACE;
			break;
		case 2 :
			this.rank = Rank.TWO;
			break;
		case 3 :
			this.rank = Rank.THREE;
			break;
		case 4 :
			this.rank = Rank.FOUR;
			break;
		case 5 :
			this.rank = Rank.FIVE;
			break;
		case 6 :
			this.rank = Rank.SIX;
			break;
		case 7 :
			this.rank = Rank.SEVEN;
			break;
		case 8 :
			this.rank = Rank.EIGHT;
			break;
		case 9 :
			this.rank = Rank.NINE;
			break;
		case 10 :
			this.rank = Rank.TEN;
			break;
		case 11 :
			this.rank = Rank.JACK;
			break;
		case 12 :
			this.rank = Rank.QUEEN;
			break;
		case 13 :
			this.rank = Rank.KING;
			break;
		default : break;
		}
	}

	@Override
    public String toString() {
        return rank.toString() + " of " + suit.toString();
    }

	@Override
	public boolean equals (Object other) {
		if (other == null) return false;
		if (!(other instanceof Card)) return false;

		if (this == other) return true;
		
		if (getClass() != other.getClass()) return false;
		
		Card card = (Card) other;
		return  card.suit == this.suit &&
				card.rank == this.rank;	
	}

protected enum Suit {
        CLUBS("Clubs"), DIAMONDS("Diamonds"), HEARTS("Hearts"), SPADES("Spades");

        private String name;
        Suit(String name) { this.name = name; }
        public String getName() { return name; }
    }

    protected enum Rank {
        ACE("Ace"), TWO("Two"), THREE("Three"), FOUR("Four"), FIVE("Five"),
        SIX("Six"), SEVEN("Seven"), EIGHT("Eight"), NINE("Nine"), TEN("Ten"),
        JACK("Jack"), QUEEN("Queen"), KING("King");

        private String name;
        Rank(String name) { this.name = name; }
        public String getName() { return name; }
    }

    protected Suit getSuit() {
        return this.suit;}

    protected Rank getRank() {
        return this.rank;
    }

    protected Suit suit;
    protected Rank rank;

}

package poker;
import java.awt.Image;

public class Deck extends Card {

	public Deck() {

		short iCount = 0;
			for (short suit = 1; suit <= 4; suit++){
				for (short rank = 1; rank <= 13; rank++) {
					this.deckOfCards.add(new Card(suit, rank));
					iCount++;
				}}
		this.readIcons();

	}

	public Deck (boolean _shuffled)
	{
		this();
		if (_shuffled == true)
		{
			Collections.shuffle(deckOfCards, new Random());
		}

	}
		public ArrayList<Card> getDeckOfCards() {return this.deckOfCards;}

		public ArrayList<Image> getCardIcons() {return this.CardIcons;}

		public Card getTopCard() {
			Card _cardRemoved = deckOfCards.get(1);
			deckOfCards.remove(1);
			return _cardRemoved;
		}

		public static final short MAX_CARDS_IN_DECK = 52;
		
		@Override
	    public String toString() {
	        return "Call .getDeckOfCards(), which returns ArrayList<Card>";
	    }

		@Override
		public boolean equals (Object other) {
			if (other == null) return false;
			if (!(other instanceof Deck)) return false;

			if (this == other) return true;
			
			if (getClass() != other.getClass()) return false;
			
			Card card = (Card) other;
			return  card.suit == this.suit &&
					card.rank == this.rank;	
		}
	
		private void readIcons(){

	    	String _filename;

	    	//read images from files
	    	Image _image = null;
	    	File _file = null;
	    	InputStream _is = null;
	    	for (int i = 1; i < MAX_CARDS_IN_DECK + 1; i++) {
	    	try {

	    		/* Security information: filenames should not be altered manually by an Administrator, and,
	    		 should be available within the same directory where the source code runs. */

	    			if (i < 10) {_filename = "0" + Integer.toString(i);}
	    			else {_filename = Integer.toString(i);}

	    			String _temp = _filename;
	    			_filename = _temp + ".GIF";

	    			//NOTE: Relative path might change when implementing?
	    			_filename = System.getProperty("user.dir") + "\\img\\" + _filename;

	    		_file = new File(_filename);

	    		//read from an input stream
	    		_is = new BufferedInputStream (new FileInputStream(_filename));

	    		_image = ImageIO.read(_is);
	    		if (_file.exists()) {
	    		CardIcons.add(_image);
	    		System.out.println("DEBUG: " + _filename + " loaded.");
	    		}
	    	}
	    	catch (IOException e) { System.out.println(e.getMessage()); }
	    	}
	    }

		private ArrayList<Image> CardIcons = new ArrayList<Image>();
		private ArrayList<Card> deckOfCards = new ArrayList<Card>();
}

[Campbell Ritchie]

We have already seen that Deck extends Class is incorrect use of inheritance. A Deck "is-not-a" Card.
There are several good references about the equals() method:

for example, if you google for Effective Java Joshua Bloch Methods inherited from Object, you might find a sample chapter from the 1st edition, which has lots about the equals() method it. you might find it here.

Angelika Langer's website. That actually appears on the Google search I told you about above

Odersky Spoon and Venners: you will find a link to their work on our FAQ.

Unsynchronized means that multiple threads can gain access to its methods simultaneously. Look in the documentation for ArrayList and the Java™ tutorials for more details.
No, an array list doesn't use a hash code as a routine.

[Jon Camilleri]

Campbell Ritchie wrote:We have already seen that Deck extends Class is incorrect use of inheritance. A Deck "is-not-a" Card.
There are several good references about the equals() method:

for example, if you google for Effective Java Joshua Bloch Methods inherited from Object, you might find a sample chapter from the 1st edition, which has lots about the equals() method it. you might find it here.

Angelika Langer's website. That actually appears on the Google search I told you about above

Odersky Spoon and Venners: you will find a link to their work on our FAQ.

Unsynchronized means that multiple threads can gain access to its methods simultaneously. Look in the documentation for ArrayList and the Java™ tutorials for more details.
No, an array list doesn't use a hash code as a routine.

Thanks I will surely go through the documentation since I am training; any idea how to represent a set of 52 cards as an object and avoid extending the Card class?

[Manjula Weerasinghe]

"Deck" is-not-a "Card" as Ritchie has pointed out. So it is not a good design to extend "Card" class for creating "Deck" class. We use extending of classes for representing "IS-A" relationship between two classes.
Relationship between "Deck" and "Card" is, "Deck" has-a (list of)"Card".
That means, "Deck" class has a reference to list of instances of "Card" class.
In your "Deck" class, you have already implemented that relationship using

private ArrayList<Card> deckOfCards = new ArrayList<Card>();

As I see, "extends Card" part in your existing class is also not required for any functionality of your current code. No harm will be done if you removed that part. But I didn't read all of your code, there may be few other changes also needs to do if you remove "extends Card" part.

[Jon Camilleri]

Manjula Weerasinghe wrote:"Deck" is-not-a "Card" as Ritchie has pointed out. So it is not a good design to extend "Card" class for creating "Deck" class. We use extending of classes for representing "IS-A" relationship between two classes.
Relationship between "Deck" and "Card" is, "Deck" has-a (list of)"Card".
That means, "Deck" class has a reference to list of instances of "Card" class.
In your "Deck" class, you have already implemented that relationship using

private ArrayList<Card> deckOfCards = new ArrayList<Card>();

As I see, "extends Card" part in your existing class is also not required for any functionality of your current code. No harm will be done if you removed that part. But I didn't read all of your code, there may be few other changes also needs to do if you remove "extends Card" part.

Thank you, you are right, however the implication that I would have to factor out the code currently within the Deck class within the main() method (and will eventually be moved to some calling program when I get to the UI design stage) seems like spaghetti to me, what is your advice?

package poker;
import java.awt.Image;
import java.io.BufferedInputStream;
import java.io.File;
import java.util.*;
import java.io.*;
import javax.imageio.ImageIO;

[b]import org.apache.log4j.Logger;
import org.apache.log4j.BasicConfigurator;
import org.apache.log4j.NDC;[/b] //not working either

public class Deck extends Card {

	public Deck() {

		short iCount = 0;
			for (short suit = 1; suit <= 4; suit++){
				for (short rank = 1; rank <= 13; rank++) {
					this.deckOfCards.add(new Card(suit, rank));
					iCount++;
				}}
		this.readIcons();

	}

	public Deck (boolean _shuffled)
	{
		this();
		if (_shuffled == true)
		{
			Collections.shuffle(deckOfCards, new Random());
		}

	}
		public ArrayList<Card> getDeckOfCards() {return this.deckOfCards;}

		public ArrayList<Image> getCardIcons() {return this.CardIcons;}

		public Card getTopCard() {
			Card _cardRemoved = deckOfCards.get(1);
			deckOfCards.remove(1);
			return _cardRemoved;
		}

		public static final short MAX_CARDS_IN_DECK = 52;
		
		@Override
	    public String toString() {
	        return "Call .getDeckOfCards(), which returns ArrayList<Card>";
	    }

		@Override
		public boolean equals (Object other) {
			if (other == null) return false;
			if (!(other instanceof Deck)) return false;

			if (this == other) return true;
			
			if (getClass() != other.getClass()) return false;
			
			Card card = (Card) other;
			return  card.suit == this.suit &&
					card.rank == this.rank;	
		}
	
		private void readIcons(){

	    	String _filename;

	    	//read images from files
	    	Image _image = null;
	    	File _file = null;
	    	InputStream _is = null;
	    	for (int i = 1; i < MAX_CARDS_IN_DECK + 1; i++) {
	    	try {

	    		/* Security information: filenames should not be altered manually by an Administrator, and,
	    		 should be available within the same directory where the source code runs. */

	    			if (i < 10) {_filename = "0" + Integer.toString(i);}
	    			else {_filename = Integer.toString(i);}

	    			String _temp = _filename;
	    			_filename = _temp + ".GIF";

	    			//NOTE: Relative path might change when implementing?
	    			_filename = System.getProperty("user.dir") + "\\img\\" + _filename;

	    		_file = new File(_filename);

	    		//read from an input stream
	    		_is = new BufferedInputStream (new FileInputStream(_filename));

	    		_image = ImageIO.read(_is);
	    		if (_file.exists()) {
	    		CardIcons.add(_image);
	    		_logger.info("DEBUG: " + _filename + " loaded.");
	    		}
	    	}
	    	catch (IOException e) { System.out.println(e.getMessage()); }
	    	}
	    }

		private ArrayList<Image> CardIcons = new ArrayList<Image>();
		private ArrayList<Card> deckOfCards = new ArrayList<Card>();
		private static Logger _logger = Logger.getLogger(poker.Deck.class);
}

I also have another little problem after having tried to rig in Apache logging services to the code.

[Stephan van Hulst]

I didn't see this thread before I answered you in your other thread here: http://www.coderanch.com/t/535373/java/java/cannot-read-Collection-custom-class#2428780

As has been proposed earlier in this thread, you should study the resources to find out more about the working of equals() and hashCode().

Thank you, you are right, however the implication that I would have to factor out the code currently within the Deck class within the main() method (and will eventually be moved to some calling program when I get to the UI design stage) seems like spaghetti to me, what is your advice?

What exactly strikes you as spaghetti? It seems like a perfectly reasonable implication.

[Jon Camilleri]

Stephan van Hulst wrote:I didn't see this thread before I answered you in your other thread here: http://www.coderanch.com/t/535373/java/java/cannot-read-Collection-custom-class#2428780

As has been proposed earlier in this thread, you should study the resources to find out more about the working of equals() and hashCode().

Thank you, you are right, however the implication that I would have to factor out the code currently within the Deck class within the main() method (and will eventually be moved to some calling program when I get to the UI design stage) seems like spaghetti to me, what is your advice?

What exactly strikes you as spaghetti? It seems like a perfectly reasonable implication.

Okay thanks, so I just have to re-factor out the code from my Deck into the Poker class, which is basically my "mother" class for processing the game.

[Stephan van Hulst]

Sounds like a good idea to me. I would also put the Dealer code in the Poker class, and trash Dealer as well.