Question

I recently made a very simple practice program in Python, that takes user input and rolls dice. The code is:

import random
import sys
import math

def roll(rolls, sides, results):
    for rolls in range(1, rolls + 1):
        result = random.randrange(1, sides + 1)
        print result
        results.append(result)
def countf(rolls, sides, results):
    i = 1
    print "There were", rolls, "rolls."
    for sides in range(1, sides + 1):
        if results.count(i) != 1:
            print "There were", results.count(i), i,"s."
        else:
            print "There was", results.count(i), i
        i = i + 1
        if i == sides:
            break
    rolls = input("How many rolls? ")
        sides = input("How many sides of the die? ")
        results = []

        roll(rolls, sides, results)
        countf(rolls, sides, results)

(actually this is part of a larger program, so I had to cut’n’paste bits, and I might have missed something out).

And so I decided to translate that to Java. Notice the algorithm here: get random number, print it, append it to an array, then count the amount of each number in the array at the end, and print out that value. Problem is, I don’t know how to do the equivalent of someArray.count(someIndex) in Java syntax. So my Java program looks like this so far:

import java.util.*;

public class Dice {
    static Scanner input = new Scanner(System.in);
    public static void main(String[] args) {
        final static int TIMES_TO_ROLL = getInt("Times to roll?");
        Random flip = new Random();
        int[] results = new int[TIMES_TO_ROLL];
        for (int i = 0; i < TIMES_TO_ROLL; i++) {
            int result = flip.nextInt(6);
            System.out.println(result);
            results[i] = result;
        }
    }
    public static int getInt(String prompt) {
        System.out.print(prompt + " ");
        int integer = input.nextInt();
        input.nextLine();
        return integer;
    }
}

So can someone help me with the array counting code? I understand that this might not be a defined method, since Python is higher level after all, so I could make my own array counting method, but I was wondering if Java, like Python, has a predefined one.

EDIT: I managed something like this:

public static int arrayCount(int[] array, int item) {
    int amt = 0;
    for (int i = 0; i < array.length; i++) {
        if (array[i] == item) {
            amt++;
        }
        else {
            amt = amt;
        }
    }
    return amt;
}

EDIT: Just out of interest, assuming I use Command prompt to run my Java program and Python.exe (command prompt console for Python), which one will be faster (in other words, for the same code, which language has better performance?)?

Answer 1

There are a couple libraries that will do this for you:

1. Google Guava’s MultiSet
2. Apache Common’s Bag

But for something so simple, you may consider an extra library a bit excessive.

You can also do this yourself with an int[]. Assuming your dice is using whole numbers, have the number rolled refer to the index into the array, and then increment the value at that index. When you need to retrieve the value for a given number, look up its value by the index.

private static final int NUMBER_DICE_SIDES = 6;
public static void main(String[] args) {
    final static int TIMES_TO_ROLL = getInt("Times to roll?");
    Random flip = new Random(NUMBER_DICE_SIDES);
    int[] results = new int[NUMBER_DICE_SIDES];
    for (int i = 0; i < TIMES_TO_ROLL; i++) {
        int result = flip.nextInt;
        System.out.println(result);
        results[result]++;
    }

    for(int i = 0; i < NUMBER_DICE_SIDES; ++i) {
        System.out.println((i+1)+"'s: " + arraysCount(results, i));
    }
}

public static int arrayCount(int[] array, int item) {
    return array[item];
}