/*
 *  File: TestRandom.java
 *  Author: Java, Java, Java
 *  Description: This program tests the java.lang.Math.random()
 *    method by simulating a six-faced die.  The die is rolled
 *    NTRIALS times ands its face value is tabulated in an array.
 *    The number of rolls for each die is printed. If the random
 *    number generator is relatively good, each die face should
 *    come up approximately 1/6 of the time.

 *  Math.random() returns a real number, r such that 0 <= r < 1
 *  Note the expression for scaling the random number to a
 *  integer value between 1 and 6 (NFACES)
 *       1 + (int)(Math.random() * NFACES)
 */

public class TestRandom {
    public static final int NTRIALS = 6000;     // Number of experimental trials
    private final int NFACES = 6;               // Number of faces on the die
    private int counter[] = { 0,0,0,0,0,0 } ;   // The six counters

    /**
     * testDie() rolls a NFACES die nTrials times
     * @param nTrials -- the number of die rolls
     * Pre: counter[] array has been initialized
     *      and nTrials, the number of trials, is >= 0.
     * Post: the frequencies of nTrials die rolls will be recorded in counter[]
     */
    public void testDie(int nTrials) {
        int die;                                     // Represents the die
        for (int k = 0; k < nTrials; k++) {          // For each trial
            die = 1 + (int)(Math.random() * NFACES); // Toss the die
            ++counter[die - 1];                      // Update the appropriate counter
        } // for
    } //testDie()

    /**
     * printResults() display's the array's values
     * Pre: counter[] array has been initialized and nTrials >= 0
     * Post: the value of each counter is printed
     */
    public void printResults(int nTrials) {
        System.out.println("Out of " + nTrials + " die rolls, there were: ");
        for (int k = 1; k <= NFACES; k++)
            System.out.println("    " + counter[k-1] + " " + k + "s");
    } // printResults()

    /**
     *  main() creates an instance of TestRandom and conducts
     *  the die rolling experiment.
     */
    public static void main(String args[]) {
        TestRandom tester = new TestRandom();
        tester.testDie(NTRIALS);
        tester.printResults(NTRIALS);
    } // main()
} // TestRandom