Java Reference
In-Depth Information
Now the call rollDice(new int[] { 1,2 } ) will change the first two dice, which seems to
be a more intuitive behavior for the method.
When our program is complete, it should run as demonstrated by the following example
(user input is in italic).
Your dice are: 3,2,5,5,1
Which dice do you want to reroll:
Your dice are: 6,5,5,5,4
Which dice do you want to reroll:
Your dice are: 5,5,5,5,5
You got Yahtzee!
Therefore, we need a method that parses user input and converts it into an array of
integers. For example, when the user enters: 1 2 5, we want to create the array
send it to the rollDice method. Fortunately, a string tokenizer class is part of the Java
library java.util.* . Below is an example use of the class.
1 public static int [] convert(String s)
StringTokenizer st = new StringTokenizer(s) ;
int [] a = new i n t [ st . countTokens () ] ;
int i=0;
while ( st . hasMoreTokens () )
a[ i++] = Integer . parseInt(st .nextToken()) ;
return a;
The first line of the code creates a new string tokenizer object from the string s .The
name of the tokenizer is st .The countTokens method returns the number of tokens in the
string. The while loop goes through all the tokens. The nextToken method returns the
next token from the string as a String ,wherethe Integer.parseInt method converts the
string to an integer. The hasMoreTokens method returns true when there are more tokens
in the string tokenizer. The convert method creates an array of integers and returns the
array. For example, the call covert("1 2 3") will return the array of integers
Note that the above code makes a clever use of the ++ operator. Line 7 uses the syntax
i++ . This means use the current value of i and then increment i by one later. The first
time Line 7 is executed, the variable a[0] will be assigned and i will change to 1. This is
exactly the desired behavior.
Our next method will check to see if the dice form a Yahtzee. The method will go through
all the dice and check if they are equal to the first die. If one of the die is not equal to the
first die, then we know that the dice are not all the same and the method will return false .
If we go through all the dice and they are all the same, then the method will return true .
public static boolean isYahtzee() {
for ( int i=0;i < NUMBER OF DICE ; i ++) {
if (dice[i] != dice[0]) {
//evidence that the dice are different
return false ;
return true ;
Novice programmers are sometimes tempted to use the if-else construct when writing
similar methods. For example, note that the following rewrite is not correct.
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