Using custom Exceptions

Question

I was wondering how I would use a custom made exception with another class. For example I am making a Card class and an invalidCardException. How can I use the methods from the Card class inside of the exception class and vice versa?

Here's an example of my card class. I need to be able to access the getSuitDesignator in my exception class.

    public class Card {
    private int cardID;  //I chose to use a single variable that could mathematically be used to transform from and to the value and suit
    //However a far simpler method would have simply stored the value and suit exactly as given by the constructor

private final int NUMBER_OF_SUITS = 4;  //By using these constants we can alter the characteristics of the cards
private final int CARDS_PER_SUIT = 13;
private final char [] CARD_SUIT_CHARS = {'H', 'S', 'C', 'D'};  //Great idea from Melissa Bruno
private final String [] CARD_SUIT_NAMES = {"Heart", "Spade", "Club", "Diamond"};
private final String [] CARD_VALUE_NAMES = {"Ace", "Two", "Three", "Four", "Five", "Six", "Seven", "Eight", "Nine", "Ten", "Jack", "Queen", "King"};



//  private Card(): creates a blank card with no suit and no value
// 1: First method set written and tested
private Card()
{
}

// Card(char suit, int value)  : creates a card of the specified suit (H, S, C, D) and value (1-13)
// 1: First method set written and tested
public Card(char inCardSuit, int inCardValue)
{
int suitSequence;

for(suitSequence = 0; suitSequence < this.NUMBER_OF_SUITS; suitSequence++)
{
if(this.CARD_SUIT_CHARS[suitSequence] == inCardSuit)
{
break;  //Suit found
}
}

this.cardID = (suitSequence * this.CARDS_PER_SUIT) + (inCardValue - 1);
}

//char getSuitDesignator() : returns char designator of card suit
// 4: Fourth method set written and tested 
public char getSuitDesignator()
{
int suitSequence = this.cardID / this.CARDS_PER_SUIT; //int Math to get the suit - originally had / and % flipped - found and fixed during testing
return this.CARD_SUIT_CHARS[suitSequence];
}

//int getValue() : returns card value (1-13)
// 4: Fourth method set written and tested 
public int getValue()
{
int cardValue = this.cardID % this.CARDS_PER_SUIT; //int Math to get the suit
return cardValue + 1; //Adding 1 to translate to a 1-13 card value (did not do this at first - found and fixed during testing)

}


//String getSuitName() : returns String name of card suit
// 2: Second method set written and tested (also altered toString to use this method
public String getSuitName()
{
int suitSequence = this.cardID / this.CARDS_PER_SUIT; //int Math to get the suit
return this.CARD_SUIT_NAMES[suitSequence];
}

//String getValueName() : returns String name of card value (i.e. “Ace”, “Two”, … , “Queen”, “King”)
// 3: Third method set written and tested (also altered toString to use this method
public String getValueName()
{
int valueSequence = this.cardID % this.CARDS_PER_SUIT; //int Math to get the suit
return this.CARD_VALUE_NAMES[valueSequence];

}

//String toString() :  returns a representation of the Card as <suit name> +  “ “ + <value name>
// 1: First method set written and tested
public String toString()
{
//return this.cardID;  // 1: As it was first written (simply for testing the constructor
//return this.getSuitName() + " " + this.cardID;  // 2: As altered for Second method set
return this.getSuitName() + " " + this.getValueName();  // 3: Final version
}

//boolean compareSuit(Card) : returns true if both cards have the same suit regardless of value
// 5: Fifth method set written and tested 
public boolean compareSuit(Card inCompareCard)
{
return inCompareCard.getSuitDesignator() == this.getSuitDesignator();
}

//boolean compareValue(Card) : returns true if both cards have the same value regardless of suit
// 6: Sixth method set written and tested 
public boolean compareValue(Card inCompareCard)
{
return inCompareCard.getValue() == this.getValue();
}

//boolean compareTo(Card) : returns true if both cards have the same value and suit
// 6: Sixth method set written and tested 
public boolean compareTo(Card inCompareCard)
{
return (this.compareValue(inCompareCard) && this.compareSuit(inCompareCard)); //reuse the methods already written -- less code and changes go everywhere
}


}

You need to extend base exception class in custom exception class and you can declare on any function with throws of type custom class. based on logic you can catch or throw further. this is only for custom exception class. — pratikpawar, Feb 11 '16 at 21:37
Can you give us example of what your Card class could look like and what methods do you need to access from the exception? Couldn't you just pass the needed values to the exception constructor? - [this might help](http://stackoverflow.com/help/mcve) — radoh, Feb 11 '16 at 21:55

hazra · Answer 1 · 2016-02-11T21:56:22.430

You need to extend the Exception class. You could create a constructor that takes a Card object and use the methods of the Card class with that object. See below for an example:

Example:

public class InvalidCardException extends Exception {
    public InvalidCardException(String message) {
        super(message);
    }

      public InvalidCardException(String message, Card card) {
        super(message);
        // do something with card object
    }
}

If you need to access that object in other methods you could assign the object to an instance variable.

Example:

public class InvalidCardException extends Exception {
    private Card card;

    public InvalidCardException(String message) {
        super(message);
    }

    public InvalidCardException(String message, Card card) {
        super(message);
        this.card = card;
    }

    public void doSomethingWithCard() {
        // use card methods
    }
}

Using custom Exceptions

1 Answers1