We can achieve this by isAlive() and join() methods of Thread class. isAlive() is not great at doing this task. So, we will be using join() method.

Threadd class — implements Runnable : 

class Threadd implements Runnable{
Thread t;
String name;

Threadd(){
name = “how”;
t = new Thread(this,name);
System.out.println(“This is thread”);
t.start();
}

public void run() {
for(int i=0;i<20;i++){
System.out.println(“This is run method”);
try{
Thread.sleep(100);
}
catch(InterruptedException e){}
}
}
}

Main Class : 

class Main{
public static void main(String args[])throws InterruptedException{
Threadd t0 = new Threadd();
Threadd t1 = new Threadd();
Threadd t2 = new Threadd();

try {
t0.t.join();
t1.t.join();
t2.t.join();
}
catch (InterruptedException e){}
System.out.println(“Main Exit”);
}
}

When you will comment the try-catch block in main method, you will see that main method will exit before other threads.