How to make the random number not repeat ?

Question

public class randomla {
public static void main(String[] args) {
double a = 0.0;
for(double i=0 ; i<5 ; i++){
a = Math.random();
System.out.println((int)(a*6));
}

Answer 1

Are you saying that you want to print 5 random unique numbers - 12, 5, 459, 2, 42 as opposed to 12, 5, 459, 12, 42?
If so you have two options:
1. Place the generated number in array or collection only if it is not already present and then when you have 5 numbers print them out (or you could print them out when generated).
2. Place all possible numbers into a collection, shuffle them and then print out the first five numbers.