How to randomly pick an element from an array

Question

I am looking for solution to pick number randomly from an integer array.

For example I have an array new int[]{1,2,3}, how can I pick a number randomly?

Answer 1

Since you have java 8, another solution is to use Stream API.

new Random().ints(1, 500).limit(500).forEach(p -> System.out.println(list[p]));

Where 1 is the lowest int generated (inclusive) and 500 is the highest (exclusive). limit means that your stream will have a length of 500.

 int[] list = new int[] {1,2,3,4,5,6};
 new Random().ints(0, list.length).limit(10).forEach(p -> System.out.println(list[p])); 

Random is from java.util package.

Answer 2

You can also try this approach..

public static <E> E[] pickRandom_(int n,E ...item) {
        List<E> copy = Arrays.asList(item);
        Collections.shuffle(copy);
        if (copy.size() > n) {
            return (E[]) copy.subList(0, n).toArray();
        } else {
            return (E[]) copy.toArray();
        }

    }

Answer 3

Java has a Random class in the java.util package. Using it you can do the following:

Random rnd = new Random();
int randomNumberFromArray = array[rnd.nextInt(3)];

Hope this helps!

Answer 4

package io.github.baijifeilong.tmp;

import java.util.concurrent.ThreadLocalRandom;
import java.util.stream.Stream;

/**
 * Created by BaiJiFeiLong@gmail.com at 2019/1/3 下午7:34
 */
public class Bar {
    public static void main(String[] args) {
        Stream.generate(() -> null).limit(10).forEach($ -> {
            System.out.println(new String[]{"hello", "world"}[ThreadLocalRandom.current().nextInt(2)]);
        });
    }
}

Answer 5

use java.util.Random to generate a random number between 0 and array length: random_number, and then use the random number to get the integer: array[random_number]

Answer 6

You can also use

public static int getRandom(int[] array) {
    int rnd = (int)(Math.random()*array.length);
    return array[rnd];
}

Math.random() returns an double between 0.0 (inclusive) to 1.0 (exclusive)

Multiplying this with array.length gives you a double between 0.0 (inclusive) and array.length (exclusive)

Casting to int will round down giving you and integer between 0 (inclusive) and array.length-1 (inclusive)