Random numbers and bubble sort

Question

I'm trying to write a little program that would allow the user to first enter a number from 9 to 18, to generate corresponding random numbers (that represent the radius), then to calculate the surface (circle) of each randomly-generated number, and finally to sort the results in descending order.

So far here's my code:

import java.util.Scanner;
import java.math.*;
public class test {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter a number from 9 to 18: ");
        int num9a18 = input.nextInt();
        if (num9a18 < 9 || num9a18 > 18) {
            System.out.println("This number is invalid!");
        }       
        int num;
        for (int i = 0; i < num9a18; i++) {
            num = randomInt(1, 6);
            System.out.print(num + " ");
        }
    }
    public static int randomInt(int small, int big) {
        double PI = 3.141592564; 
        int results = ((int) (Math.random() * (big - small + 1)) + small);
        return results*results*PI;
    }
} 

Can you give me some tips because I'm kind of stuck here.

Answer 1

Your program will have compilation error due to int - double inconsistency

Modified your program to fix that, as well as the one that you probably is looking for.

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import java.util.Scanner;

public class Test {
    public static void main(String[] args) {
        Scanner input = new Scanner(System.in);
        System.out.println("Enter a number from 9 to 18: ");
        int num9a18 = input.nextInt();
        if (num9a18 < 9 || num9a18 > 18) {
            System.out.println("This number is invalid!");
        }
        double result;
        List<Double> results = new ArrayList<Double>();
        for (int i = 0; i < num9a18; i++) {
            result = resultFromRandomRadius(1, 6);
            results.add(result);
        }
        System.out.println("................SORTING.................");
        Collections.sort(results);
        for (double res : results) {
            System.out.println(res);
        }
        System.out.println("..........................................");
        System.out.println("................REVERSING.................");
        Collections.reverse(results);
        for (double res : results) {
            System.out.println(res);
        }
    }

    public static double resultFromRandomRadius(int small, int big) {
        double PI = 3.141592564;
        int results = ((int) (Math.random() * (big - small + 1)) + small);
        return results * results * PI;
    }
}

Note: I'm making use of auto-boxing feature supported since Java 1.5

Update: Updated the code to demonstrate reverse() as well

Output:

Enter a number from 9 to 18:

10

................SORTING.................

3.141592564
3.141592564
12.566370256
12.566370256
28.274333076
78.5398141
78.5398141
78.5398141
113.097332304
113.097332304

.......................................... ................REVERSING.................

113.097332304
113.097332304
78.5398141
78.5398141
78.5398141
28.274333076
12.566370256
12.566370256
3.141592564
3.141592564