Generating Unique Random Numbers in Java

Question

I\'m trying to get random numbers between 0 and 100. But I want them to be unique, not repeated in a sequence. For example if I got 5 numbers, they should be 82,12,53,64,32

Answer 1

you can use boolean array to fill the true if value taken else set navigate through boolean array to get value as per given below

package study;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

/*
Created By Sachin  Rane on Jul 18, 2018
*/
public class UniqueRandomNumber {
    static Boolean[] boolArray;
    public static void main(String s[]){
        List integers = new ArrayList<>();


        for (int i = 0; i < 10; i++) {
            integers.add(i);
        }


        //get unique random numbers
        boolArray = new Boolean[integers.size()+1];
        Arrays.fill(boolArray, false);
        for (int i = 0; i < 10; i++) {
            System.out.print(getUniqueRandomNumber(integers) + " ");

        }

    }

    private static int  getUniqueRandomNumber(List integers) {
        int randNum =(int) (Math.random()*integers.size());
        if(boolArray[randNum]){
            while(boolArray[randNum]){
                randNum++;
                if(randNum>boolArray.length){
                    randNum=0;
                }
            }
            boolArray[randNum]=true;
            return randNum;
        }else {
            boolArray[randNum]=true;
            return randNum;
        }

    }

}