methods

[blueduiker]

Hey guys so in a class that I have to make called Card, I need to make a method called compareTo(). How do I instantiate the parameter which is Card c?

/*returns 1 if this card has higher value,
	  returns -1 if c has higher value,
	  returns 0 if they have equal value */
		public int compareTo (Card c) {
			Card c = new Card(c.

		}

[masijade]

The "parameter" is an already instantiated Card Object. You need only compare it's values to the values from "this".

[blueduiker]

public class Card {
	
	//Instance Data
		public static String []  theRanks = {"Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King", "Ace"};
		public static String [] theSuits = {"Hearts", "Clubs", "Diamonds", "Spades"};
		private int value;
		int suitNum;
		int rankNum;
  
	//Constructor - value is between 0-51 inclusive
		public Card (int val) {
			value = val;
			suitNum= val / 13;
			rankNum = val % 13;
		}
   
		
	//toString Method
		public String toString() {
			String s = getRank() + " of " + getSuit();
			return s;
		}
 
		
	//returns the card's Rank Number 
		public int getRankNum() {
			return rankNum;
		}
 
		
	//returns card's Suit Number
		public int getSuitNum() {
			return suitNum;
		}
 
	
	//return cards Rank in String form
		public String getRank() {
			return theRanks [rankNum];
		}
		
		
	//returns
		public String getSuit() {
			return theSuits [suitNum];
		}
 
		
	/*returns 1 if this card has higher value,
	  returns -1 if c has higher value,
	  returns 0 if they have equal value */
		public int compareTo (Card c) {
			Card c = new Card(c.

		}  
}

[blueduiker]

Sorry, what is "this"?
Is it the card that was made in my constructor class originally?

[r035198x]

You don't need to instantiate it. The parameter indicates that the method is going to be passed an already instantiated Card so the method has one less thing to worry about.

[masijade]

"this" is, of course, the object instance on which compareTo is called. It is the "current" instance of the object, so to say. The way that method will be called is as follows:

Card a = new Card();
Card b = new Card();
int result = a.compareTo(b);

so the compareTo method of "a" will be called. So, any reference to "this" in that method will refer to the values in "a" (in that instance).

[blueduiker]

Ok, I think I got it.
Thanks everyone!

[blueduiker]

+1 rep for everyone

[blueduiker]

does this look right for the compareTo() method?

/*returns 1 if this card has higher value,
	  returns -1 if c has higher value,
	  returns 0 if they have equal value */
		public int compareTo(Card c) {
			int result = 9001;
			
			if (getRankNum() > c.getRankNum())
				result = 1;
			if (getRankNum() < c.getRankNum())
				result = -1;
			if (getRankNum() == c.getRankNum())
				result = 0;
			
			return result;
		}

[masijade]

Not terribly effecient, but it will work.

[blueduiker]

ok, thanks

[m00nchile]

Just a tip. compareTo() doesn't need to return specific values, just a range, negative if the first object is lesser, positive if it's greater, or 0 if the two objects are equal. So to simplify, and optimize, your example, you could simply do:

public int compareTo(Card c) {
       return getRankNum() - c.getRankNum();
}

So, instead of 6 calls to the getRankNum() method, you now only have 2, and when you call the compareTo() method in your program, instead of

if(a.compareTo(b) == -1) //testing, if a is less than b

you now do this:

if(a.compareTo(b) < 0)

Another benefit to this way of comparing the cards is, you know how far apart they are, if you happen to need this information.

[JosAH]

... also, given your code, better compare the Card's 'value' because their rank doesn't take a Card's suit in account.

kind regards,

Jos