Trying to randomize the number index in my Arraylist

Question

Im currently trying to run a program that has the user input a number and have the program select the word. However I can't seem to get the program to function right. I am able to have the program run without having the index changed. Is there something I am missing here? I've imported the Random function but am having trouble figuring out the last part. All this is being done in NetBeans.

package arraywords;

import java.util.Scanner;
import java.util.ArrayList;
import java.util.Random;

public class Arraywords {
    public static void main(String[] args) {
        ArrayList<String>words = new ArrayList();
        words.add("Token");
        words.add("Magic");
        words.add("People");
        words.add("Racecar");
        words.add("Xbox");
        words.add("Puppy");
        words.add("Destiny");
        words.add("Knowledge");
        words.add("Home");
        words.add("Professional");

        System.out.print("Choose a random number between 1 and 10 "
        + "to recieve a random word:\n");

        int choice = 0;
        Scanner scanner = new Scanner(System.in);//Scanner program
        while (choice < 1 || choice > 10) {//The parametors for the users
            System.out.println("Input a number:");
            String message = scanner.next();//Prompt for user to input a number
            try{
                choice = Integer.parseInt(message);
            } 
            catch(NumberFormatException e){
                System.out.print("Please use numbers");
            } /* The while loop watches the users input and is waiting for the user to input a number. Once they select a number. The word should be displayed. */
        }
        Integer index = choice -1; /* Since arrays begin with zero I had to account for that by adding the -1.  */
        System.out.printf("You entered #%d:\n> %s.", choice, words.get(index)); //Once the user has chosen a number the word will be displayed
    } 
}

Your program is running alright. What's the problem you are facing? — Yash, Oct 25 '17 at 03:22
It works for me... only thing I would improve is to close the scanner in the end. — Stefan, Oct 25 '17 at 03:28
I was trying to get a randomize number but after some thinking I realized that I could just use Math.random(); — Corey Williams, Oct 25 '17 at 03:32

score 1 · Answer 1 · answered Oct 25 '17 at 03:28

YOu are importing the random class but you are not using it in the code you posted...

you can get a random element doing

words.get(r)

where r is

Random rnd = new Random();
int r = rnd.nextInt(words.size());

there are other ways to do that (expensive ones) like shuffling the list and getting the 1st element after that operation.

score 0 · Accepted Answer · answered Oct 25 '17 at 03:39

You might just try using a random function for Java 1.7+

package arraywords;

import java.util.ArrayList;
import java.util.concurrent.ThreadLocalRandom;


public class Arraywords {
    public static void main(String[] args) {
        ArrayList<String>words = new ArrayList();
        words.add("Token");
        words.add("Magic");
        words.add("People");
        words.add("Racecar");
        words.add("Xbox");
        words.add("Puppy");
        words.add("Destiny");
        words.add("Knowledge");
        words.add("Home");
        words.add("Professional");

        int index = ThreadLocalRandom.current().nextInt(0, words.size());
        System.out.printf("Random Word Index:#%d:\n> %s.", (index+1), words.get(index));
    } 
}

Reference: How do I generate random integers within a specific range in Java?

Your right I should just use a simpler method than what I am currently using. — Corey Williams, Oct 25 '17 at 03:42

Trying to randomize the number index in my Arraylist

2 Answers2