Introduction to Arrays - Learning Java Through Games - page 92

2000

main rollDice

location: 2000

1 3 5

FIGURE 5.2: Passing an array to a method.

Although not perfect, the above code demonstrates a clean design. Every method is short
and does exactly one thing. The major shortcoming is that methods that do not need to
have access to the array of dice, such as the convert method, do anyway. This shortcoming
comes from declaring the array of dice a global variable. As an alternative, the array of dice
can be declared as a local variable in the main method and passed to methods that need it.
The new version of the main method is shown next.
public static void main(String [] args)

{
int [] dice = new i n t [ NUMBER OF DICE ] ; // the dice
Scanner keyboard = new Scanner(System. in) ;
rollDice(dice);

for ( int i=0;i < NUM REROLLS ; i ++) {
if (isYahtzee(dice)) {// if we got Yahtzee
break ;
System.out . println(diceToString(dice)) ; //prints the dice
System. out . print ( "Which dice do you want to reroll: " );
rollDice(dice ,convert(keyboard.nextLine()));
System.out . println(diceToString(dice)) ; //prints the dice
if (isYahtzee(dice)) {
System. out . println ( "You got Yahtzee!" );

} else {

System. out . println ( "Sorry, better luck next time!" );

}

}

Note that arrays in Java are passed to/from methods using their address. Therefore, the
rollDice method can and does change the value of the input array. An implementation of
the method is shown below.
public static void rollDice( int [] d) {

for ( int i=0;i < NUMBER OF DICE ; i ++) {

d[ i ] = getRandomDieValue () ;

}

}

Figure 5.2 shows an example of passing the array to the rollDice method. As the figure
suggests, only the number 2000 is passed to the method. This is the location of the array.
Since the rollDice method knows this location, it can go to it and modify the content
of the array. Note that this contrasts the way primitive types (e.g., integers, doubles, and
characters) are sent to methods. The latter cannot be modified by a method. For example,
consider the following version of the rollDice method.
public static void rollDice( int d0 , int d1 , int d2 , int d3 , int d4) {