Print odd and even numbers with thread T1 and T2 respectively, If prime number comes, print in reverse order

I recently had an interview with Morgan Stanley and was asked this question. I had to print all odd numbers when thread T1 is running and even numbers when T2 is running, but hey! there is more, If any prime number comes up then I had to reverse the order meaning now odd numbers with T2 and even numbers with T1.

Below is what I had tried but that guy looked at me like he wants to put me in jail for this solution. I'm new to multi-threading. There might be a way to establish the communication between multiple threads to achieve this using notify() and wait() methods. Could someone pull me out of that jail?

notify()

wait()

public class MainClass extends Thread
@Override
public void run()
for(int i=0;i<20;i++)
String tname = Thread.currentThread().getName();
if(isPrime(i))
switch(tname)
case "T2":
if(i%2 != 0)
System.out.println(tname + " - "+i);
break;
case "T1":
if(i%2 == 0)
System.out.println(tname + " - "+i);
break;
default:break;

else
switch(tname)
case "T1":
if(i%2 != 0)
System.out.println(tname + " - "+i);
break;
case "T2":
if(i%2 == 0)
System.out.println(tname + " - "+i);
break;
default:break;




public boolean isPrime(int num)
if(num <= 1) return false;
if(num == 2) return true;
for(int i=2;i<=num/2;i++)
if(num%i == 0)
return false;

return true;

public MainClass(String name)
super(name);

public static void main(String args)
MainClass t1 = new MainClass("T1");
MainClass t2 = new MainClass("T2");
t1.start();
try
t1.join();//always keep it inside the try otherwise compile time error
catch(InterruptedException ie)
ie.printStackTrace();

t2.start();




And here is the output.

T1 - 1
T1 - 2
T1 - 9
T1 - 15
T2 - 0
T2 - 3
T2 - 4
T2 - 5
T2 - 6
T2 - 7
T2 - 8
T2 - 10
T2 - 11
T2 - 12
T2 - 13
T2 - 14
T2 - 16
T2 - 17
T2 - 18
T2 - 19


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