Question

● Change the Deck class into a Singleton class.

● Change the main method to get the Deck instance rather than creating a new object.

● The program should print all 52 cards in random order

import java.util.*;

enum Suit {
SPADES,
HEARTS,
CLUBS,
DIAMONDS
}

class Card {
public Card(Suit s, int n) {
suit = s;
if((n < 2) || (n > 14)) {
throw new IllegalArgumentException( );
}
number = n;
}

public void print( ) {
switch(number) {
case 11:
System.out.print("Jack");
break;
case 12:
System.out.print("Queen");
break;
case 13:
System.out.print("King");
break;
case 14:
System.out.print("Ace");
break;
default:
System.out.print(number);
break;
}
System.out.print(" of ");
switch(suit) {
case SPADES:
System.out.println("spades.");
break;
case HEARTS:
System.out.println("hearts.");
break;
case CLUBS:
System.out.println("clubs.");
break;
case DIAMONDS:
System.out.println("diamonds.");
break;
}
}

private Suit suit;
private int number;
}

class Deck {
public Deck( ) {
cards = new ArrayList<Card>( );

// build the deck
Suit[] suits = {Suit.SPADES, Suit.HEARTS, Suit.CLUBS, Suit.DIAMONDS};
for(Suit suit: suits) {
for(int i = 2; i <= 14; i++) {
cards.add(new Card(suit, i));
}
}

// shuffle it!
Collections.shuffle(cards, new Random( ));
}

public void print( ) {
for(Card card: cards) {
card.print( );
}
}

private List<Card> cards;
}

public class SingletonExercise {
public static void main(String args[]) {
Deck deck = new Deck( );
deck.print( );
}
}

Answer 1

import java.util.*;

enum Suit {
   SPADES,
   HEARTS,
   CLUBS,
   DIAMONDS
}

class Card {
   public Card(Suit s, int n) {
       suit = s;
       if((n < 2) || (n > 14)) {
           throw new IllegalArgumentException( );
       }
       number = n;
   }

   public void print( ) {
       switch(number) {
           case 11:
           System.out.print("Jack");
           break;
           case 12:
           System.out.print("Queen");
           break;
           case 13:
           System.out.print("King");
           break;
           case 14:
           System.out.print("Ace");
           break;
           default:
           System.out.print(number);
           break;
       }
       System.out.print(" of ");
       switch(suit) {
           case SPADES:
           System.out.println("spades.");
           break;
           case HEARTS:
           System.out.println("hearts.");
           break;
           case CLUBS:
           System.out.println("clubs.");
           break;
           case DIAMONDS:
           System.out.println("diamonds.");
           break;
       }
   }

   private Suit suit;
   private int number;
}

class Deck {

   private static Deck instance = null;

   private Deck( ) {
       cards = new ArrayList<Card>( );

// build the deck
       Suit[] suits = {Suit.SPADES, Suit.HEARTS, Suit.CLUBS, Suit.DIAMONDS};
       for(Suit suit: suits) {
           for(int i = 2; i <= 14; i++) {
               cards.add(new Card(suit, i));
           }
       }

// shuffle it!
       Collections.shuffle(cards, new Random( ));
   }

   public static synchronized Deck getInstance()
   {
       if(instance == null)
           instance = new Deck();
       return instance;
   }

   public Object clone() throws CloneNotSupportedException {
       throw new CloneNotSupportedException("Clone is not allowed.");
}

   public void print( ) {
       for(Card card: cards) {
           card.print( );
       }
   }

   private List<Card> cards;
}

public class SingletonExercise {
   public static void main(String args[]) {
       Deck deck = Deck.getInstance();
       deck.print( );
   }
}