Methods and Formatted Output - Learning Java Through Games - page 76

}

It prompts the player to enter a choice and repeatedly reads the choice until a valid
choice is made. One may ask if the number 7 is a magic number. If it is, should it not be
declared as a constant? The answer is that declaring the number 7 as a constant will not be
very helpful here. We cannot change the number of choices just by changing this number.
Therefore, the number of choices is not really a parameter of the program and it does not
need to be declared as a constant. You can think of this as being an exception when it is
allowable to create a magic number.
The currencyFormatter method is shown next. It uses the DecimalFormat class to
format the dollar amounts in a pretty way.

{
DecimalFormat myFormatter = new DecimalFormat( "$###,###.00" );
return myFormatter . format (amount) ;

public static String currencyFormatter( double amount)

}

Note that the two zeros after the decimal dot mean that two digits will always be
displayed after the decimal dot. If the amount is 32 dollars, for example, then

32.00 will
be displayed. Conversely, the character # is non-imposing and suggests that there can be
up to 6 digits, but missing digits will not be filled with zeros.
The computePrice method is shown next.
public static double computePrice( double basePrice , double variation)

$

{

double result = basePrice;
if (Math . random() > 0.5)

{

result += Math.random() variation ;

∗

} else {
result − = Math . random() ∗ variation ;
return (( int )(result ∗ 100))/100.0;

}

It starts with the basePrice . Then a random number is used to decide if we want to
add or subtract from it. Up to the value of the variable variation can be added or removed
from the variable result . Recall that Math.random returns a number between 0 inclusive
and 1 exclusive. After executing the first 6 lines, the value of the variable result can be
10.32544, for example. However, we want the number to have only 2 digits after the decimal
dot because it must be of type currency. If we multiply the number by 100, we will move the
decimal dot two places to the right. For example, we may get the number 1032.544. Now,
we can convert the result to an integer and remove everything after the decimal dot. We
will get the number 1032. Finally, we can convert the number back to decimal by dividing it
by 100.0. We will get 10.32, which is exactly what we wanted. Note that we need to divide
by 100.0 and not by 100. If we divide by 100, we will get the result 10 because the result of
dividing two integers is always an integer. Note that the whole method can be rewritten in
a single line as follows.

public static double computePrice( double basePrice , double variation) {

return (( int ) ( ( bas ePr i ce + (Math . random ( ) > 0.5 ? 1 : − 1) variation

∗

) ∗ 100))/100.0;

}

However, this syntax uses the conditional operator and is less intuitive. In general, avoid
writing code that is non-trivial to understand.
The getQuantity method is shown next. The method is very general in that it can
be used to ask for any product and any action. Creating a method that is as reusable as