This page is part of the Blackjack Lab.
A BlackjackCard represents a playing card used for Blackjack. Responsibilities include returning the numeric value according to Blackjack rules and returning a string representation.
Start files:
Solutions are at the bottom of this page.
Provided code
Constants
Constants are provided for the values of several specific cards (ex: JACK_VALUE). The constant FACE_CARD_NUMERICAL_VALUE is also provided. These constants are used throughout both the documentation and the code.
Magic numbers are numeric literals that appear within code (ex: 10). Using constants instead of magic numbers makes code easier to read and maintain.
For example, the first conditional statement in the constructor could be written as:
if(! (1 <= value && value <= 13) )
Instead, the statement is written as:
if(! (ACE_VALUE <= value && value <= KING_VALUE) )
Using the constants makes the intent clearer.
The public constants (ex: ACE_VALUE) are intended for use both inside and outside BlackjackCard. The private constant FACE_CARD_NUMERICAL_VALUE is intended for use only within BlackjackCard.
Instance variables
BlackjackCard stores value and suit. The values are set directly to the constructor parameters. The documentation for the constructor describes the valid values.
No other instance variables should be added.
BlackjackCard constructor
The constructor accepts only value valid values for value and suit. Passing invalid values results in an IllegalArgumentException. This behavior makes errors in client code (code that uses BlackjackCard) easier to identify.
getValue and getSuit methods
getValue and getSuit are simple accessor methods. The instance variables value and suit are provide. The accessor methods provide the values of these variables to client code.
A BlackjackCard is immutable. Neither the value nor the suit can be changed after the card is constructed. There is no setValue method.
Code to be written
isAce method
Aces are handled differently than other cards. The isAce allows client code to be written more cleanly. The isAce method is not strictly required.
Client code could write:
if(card.getValue() == BlackjackCard.ACE_VALUE)
The isAce method allows the code to be more cleanly written as:
if(card.isAce())
Many classes contain methods that exist to allow cleaner client code. The java.util.ArrayList class provides both add(int, E) and add(E). The 2 parameter add method can be used to add a value to the end of a list; however, the single parameter method allows that code to be written more cleanly.
getNumericalValue method
In Blackjack, the numerical value of numbered cards (2 - 10) is the number. All face cards are worth 10 (FACE_CARD_NUMERICAL_VALUE). getNumericalValue returns 1 (ACE_VALUE) for an ace.
getNumericalValue is an accessor method. It should not change the value of the instance variable value.
toString method
toString is responsible for returning a string representation. Examples are provided in the Javadoc.
toString is an accessor method. It should not change the values of either instance variable (value or suit).
Hints
isAce method
Compare the value of the instance variable value against the constant ACE_VALUE.
getNumericalValue method
Handle the special cards first. Face cards (jack, queen, and king) and aces are special.
The value of numbered cards (2 - 10) is value.
toString method
Handle each special card first. The special cards are the same as in getNumericalValue, though each must be handled separately, unlikely in getNumericalValue.
All of the numbered cards can be handled with a single statement.
Solution code
isAce method
public boolean isAce()
{
return value == ACE_VALUE;
}
The instance variable value already stores the information necessary to determine if this BlackjackCard is an ace. No additional instance variable should be stored. See Duplicate data as instance variables.
getNumericalValue method
public int getNumericalValue()
{
if(value >= JACK_VALUE)
return FACE_CARD_NUMERICAL_VALUE;
else
return value;
}
As with isAce, the existing instance variable value stores all necessary information. value should not be modified, nor should an additional instance variable be stored.
toString method
public String toString()
{
String asString = "";
if(value == ACE_VALUE)
asString += "A";
else if(value == JACK_VALUE)
asString += "J";
else if(value == QUEEN_VALUE)
asString += "Q";
else if(value == KING_VALUE)
asString += "K";
else
asString += value;
asString += suit;
return asString;
}