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public final class Card implements Comparable{
  private String suit;
  private int rank;

  public Card(String s, int r) {
    if (s == null)
      throw new NullPointerException();
    suit = s;
    rank = r;
  }

  public boolean equals(Object o) {
    if (o instanceof Card) {
      Card c=(Card)o;
      return suit.equals(c.suit) && (rank == c.rank); // good
    }
    return false;
  }

  // this method fulfills its contract
  public int compareTo(Object o) {
    if (o instanceof Card) {
      Card c=(Card)o;
      if( suit.equals(c.suit) &&
          (c.rank >= rank + Integer.MIN_VALUE) &&
          (c.rank <= rank + Integer.MAX_VALUE) ) 
        return c.rank - rank;
      return suit.compareTo(c.suit);
    }
    throw new ClassCastException();
  }

  public static void main(String[] args) {
    Card a = new Card("Clubs", 2);
    Card b = new Card("Clubs", 10);
    Card c = new Card("Hearts", 7);
    System.out.println(a.compareTo(b)); // returns 0
    System.out.println(a.compareTo(c)); // returns a negative number
    System.out.println(b.compareTo(c)); // returns a negative number
  }
}