在Java中找到两个随机数之间的平均值，然后计算使用switch语句将一个数字滚动多少次

Question

Hello again StackOverflow,

New question needing help with some code. So far I'm making a random number generator that will choose a random number between 1-100 for rolls and then roll a "die" for a number between 1-6 . It then prints out every roll and number rolled up to said a random number between 1-100.

The problem I'm having is this. Let's be simple and say that the random number generated between 1-100 is 9 and the die rolls in order for each roll is

1, 6, 3 , 5, 4, 2, 1, 6, 6

The output is fine and the averaging is fine. The new problem I have is this:

Add to the program a switch statement to keep track of how many times each number comes up.

I have a basic idea on how to do this but I am a bit confused on how to actually go along with this and execute it. Help please

My Current Code: (UPDATE: The first problem has been solved, the new problem is said above)

        class Main {
  public static void main(String[] args) 
  {

    int rolls = (int)(Math.random()*100);
    System.out.println("Number of Rolls: "+ rolls);

    System.out.println(" ");
    System.out.println("Rolls\t\tNumber");

    double sum = 0;
    for (int i = 1; i <= rolls ; i++)
      {
        int dienumber = (int)(Math.random()*6+1);    
        sum += dienumber;
        System.out.println(i + "\t\t" + dienumber);
      }

    double average = sum /(1.0*rolls);

    System.out.println(" ");
    System.out.printf("%-2s%.2f\n","Average: ", average);

  }
}

Thanks again

Answer 1

Sum all the random numbers in a variable, and divide by number of rolls

double sum = 0;
for (int i = 1; i <= rolls ; i++) {
    int dienumber = (int)(Math.random()*6+1);
    sum += dienumber;
    System.out.println(i + "\t\t" + dienumber);
}
double avg = sum / rolls;

Answer 2

You can as well collect you random numbers into an array and calculate average using streams:

int rolls = (int)(Math.random()*100);
int rollsArray[] = new int[rolls];
for (int i = 1; i < rollsArray.length ; i++)
{
    rollsArray[i] = (int)(Math.random()*6+1);

}
System.out.println(Arrays.stream(rollsArray).average()); 
// example output OptionalDouble[3.0]

Answer 3

You can create a int variable that will count the total inside the loop after each roll. After the loop, just divide this total by your number of rolls.

class Main {
     public static void main(String[] args) 
    {

        int rolls = (int)(Math.random()*100);
        int total =0
        System.out.println("Number of Rolls: "+ rolls);

        System.out.println(" ");
        System.out.println("Rolls\t\tNumber");
        for (int i = 1; i <= rolls ; i++)
        {
            int dienumber = (int)(Math.random()*6+1);    
            System.out.println(i + "\t\t" + dienumber);
            total += dienumber; 
        }
        double average = total /(1.0d*rolls);
        System.out.println("Average = "+average);
    }
}

Answer 4

This generates a number in the range [0, 99], not [1, 100]:

int rolls = (int)(Math.random()*100);

Performance-wise it's a good idea to re-use a Random instead of calling Math.random repeatedly:

public class Main {

    private static final Random RANDOM = new Random();

    public static void main(String[] args) {
        int rolls = RANDOM.nextInt(99) + 1;

Note that, if you ever use randomness for generating security sensitive things like activation codes, use SecureRandom instead.

To calculate the average just keep track of the sum:

int sum = 0;
for (int i=1; i <= rolls ; i++) {
    int dienumber = RANDOM.nextInt(6) + 1;    
    System.out.println(i + "\t\t" + dienumber);
    sum += dieNumber;
}
double average = ((double) sum) / rolls;
System.out.printf("Average: %s%n", average);

You could also create a separate class to calculate the average, be all object-oriented and score brownie points for effort:

public class Average {

    private double total;
    private int count;

    public synchronized void add(double value) {
        total += value;
        count++;
    }

    public double getAverage() {
        if (count == 0) {
            throw new IllegalStateException("Cannot calculate average, no values added");
        }
        return total / count;       
    }

    public double getTotal() {
        return total;
    }

    public int getCount() {
        return count;
    }

    public synchronized void reset() {
        total = 0;
        count = 0;
    }
}

And your code would use this like so:

Average average = new Average();
for (int i=1; i <= rolls ; i++) {
    int dienumber = RANDOM.nextInt(6) + 1;    
    System.out.println(i + "\t\t" + dienumber);
    average.add(dieNumber);
}
System.out.printf("Average: %s%n", average.getAverage());

EDIT: As a general rule of thumb, when someone (or your homework assignment) tells you to add a switch statement: don't do it. Switch statements are evil pools of gunk which accumulate demons and reek of the foul stench of a project room filled with 2000 PHP developers. Don't. (I can recommend reading Clean Code by Uncle Bob )

But seriously: keeping track of how many times a number comes up is a valid requirement. Telling the developer to use a switch statement for this is not. This is a tendency you will come across a lot with users: they tend to specify the solution they envision, instead of formulating the problem they want to solve. This is dangerous, since if you buy into it you may very well start off on the wrong foot. The solution suggested by stakeholders is very often not optimal and rooted in their past domain experience, not technical and design knowledge. </rant>

Instead, in this case, use a Map to keep track of the outcomes. If the cases are more diverse than just keeping track of a value like here, revert to the strategy pattern to solve the problem in an object-oriented way.

Since I already proposed the lovely 'Average' class we can rename this to 'Statistics' and adorn it with a Map:

public class Statistics {

    private int total;
    private int count;
    private Map<Integer, Integer> distribution = new HashMap<>();

    public synchronized void add(int value) {
        total += value;
        count++;
        updateDistribution(value);
    }

    private void updateDistribution(int value) {
        Integer count = distribution.get(value);
        if (count == null) {
            count = 0;
        }
        count++;
        distribution.put(value, count);

    public double getAverage() {
        if (count == 0) {
            throw new IllegalStateException("Cannot calculate average, no values added");
        }
        return total / count;       
    }

    public double getTotal() {
        return total;
    }

    public int getCount() {
        return count;
    }

    public synchronized void reset() {
        total = 0;
        count = 0;
        distribution.clear();
    }

    public int getCount(int value) {
        Integer count = distribution.get(value); 
        if (count == null) {
            count = 0;
        }
    }
}

Answer 5

Functional approach (Java 1.8+):

{
    // ...
    double average = IntStream.range(0, rolls)
            .map(this::roll)
            .average()
            .orElse(0);
    System.out.println("Average : " + average);

}

private int roll(int i) {
    int dieNumber = (int) (Math.random() * 6 + 1);
    System.out.println(i + "\t\t" + dieNumber);
    return dieNumber;
}