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I am trying to build a lotto machine using java. This is the code:
import java.util.Scanner;
import java.util.Random;
import java.util.Random;
public class wissam {
public static void main(String[] args) {
int counter = 0;
int[] lottoNumbers = new int[6];
for (int x = 0; x < lottoNumbers.length; x++) {
Random rand = new Random();
lottoNumbers[x] = rand.nextInt(42) + 1;
}
int[] userChoice = new int[6];
System.out.println("Enter a number");
Scanner scan = new Scanner(System.in);
userChoice[0] = scan.nextInt();
for (int y = 1; y < userChoice.length; y++) {
System.out.println("Enter another number");
userChoice[y] = scan.nextInt();
}
for (int x = 0; x < lottoNumbers.length; x++) {
System.out.print(lottoNumbers[x] + " ");
}
System.out.println("");
for (int z = 0; z < userChoice.length; z++) {
for (int a = 0; a < lottoNumbers.length; a++) {
if (lottoNumbers[z] == userChoice[a]) {
counter++;
int b = lottoNumbers[z];
System.out.print("The common numbers were" + b + "");
}
}
}
if (counter == 0) {
System.out.println("You are such a loser");
}
}
}
It asks the user to input 6 numbers and works fine, as long as the user chooses 6 distinct numbers between 1 and 42.
I want to check if the user inputs distinct numbers that are between 1 and 42, and if they aren't I want to ask the user to change the number. How do I do that?

I would not use an array. I would use a Set. It has the function 'contains'. So whenever the users gives another number, you can check if the Set so far already contains the number.

I would do it this way
public static void main(String[] args) {
final ArrayList<Integer> userChoice = new ArrayList<>(6);
// Scan numbers
Scanner scan = new Scanner(System.in);
while (userChoice.size() < 6) {
System.out.println("Enter a number");
int choice = scan.nextInt();
if (choice < 1 || choice > 42) {
System.out.println("Number not between 1 and 42");
continue;
}
if (userChoice.contains(choice)) {
System.out.println("Number already chosen");
continue;
}
userChoice.add(choice);
}
System.out.println("You have chosen: " + userChoice);
}

Considering that you're almost there, the simplest case would be to create nested loops and before you store the number, check that it's not already within the array.
for (int y = 1; y < userChoice.length; y++) {
System.out.println("Enter another number");
boolean flag = false;
int result = scan.nextInt();
if(result < 1 || result > 42){
System.out.println("please enter a number between 1 - 42 inclusive");
y--;
continue;
}
for(int i = 1; i < userChoice.length; i++){
if(result == userChoice[i]){
flag = true;
break;
}
}
if(flag){
System.out.println("Enter a different number");
y--;
}else{
userChoice[y] = result;
}
}