How to write a java code using threads?

import java.util.*;
public class JavaOnlineTest {

public static String questions(){
Scanner sc=new Scanner(System.in);
int output=0;
System.out.println("1)Who is the 45th president of USA?");
System.out.println("1.Barrack Obama 2.Hillary Clinton 3.Donald Trump 4.George W Bush");
int answer=sc.nextInt();
if(answer==3)
output+=1;
else
output+=0;
System.out.println("2)Who is the 1st Prime Minister of India?");
System.out.println("1.Subash Chandra Bose 2.Jawahar Lal Nehru 3.Sardar Vallabhai Patel 4.Mahatma Gandhi");
answer=sc.nextInt();
if(answer==2)
output+=1;
else
output+=0;
//proceed for 3rd question here.
System.out.println("Your result out of 10 is "+output);
if(output>=0&&output<5){
System.out.println("You've Failed");
}else if(output>4 && output<8){
System.out.println("Your in B Class");
}else if(output>7 && output<=10){
System.out.println("Your in A Class");
}
System.out.println("Do you want to retake the test");
System.out.println("Type 'Y' or 'N'");
String retaking=sc.next().trim();
return retaking;
}

public static void main(String [] args){

boolean retake;

String retaking;


while(true){
retaking=questions();
if(retaking.equalsIgnoreCase("Y")){
retake=true;


}else if(retaking.equalsIgnoreCase("N")){
System.out.println("Good Luck!...");
retake=false;
retaking="N";
break;

}
}


}
}