Use a Thread to Nag Someone

In Java, we normally run code serially one instruction at a time. So if we ask someone to input his name, like this:

static final Scanner console = new Scanner(System.in);

public static void main(String[] args) {

	System.out.print("What is your name? ");
	String name = console.nextLine().trim();  // wait for input
	System.out.println("Hello "+name);

}

our code will wait (block) at console.nextLine() until the user types something and presses Enter.

The example code shows how to use a separate thread to print nag messages.

Two points to note:

1. Method Reference for Runnable

The parameter to new Thread( ) is an object that implements Runnable. Instead of writing a separate class, the code uses a method reference new Thread(Greeter::nag).

2. How to Stop the Nag Thread

The nag thread will nag the user forever, unless interrupted. After the user types his name, use:

nag.interrupt();

Inside the thread's run method (nag()), check for interruption 2 ways:

try {
    while(true) {
        Thread.sleep(2000);       // may throw InteruptedException
        if (Thread.interrupted()) break;
        System.out.println( getNagMessage() );
    }
    catch(InteruptedException ex) {
        // stop nagging
    }
}

probably the try - catch(InterruptedException) is enough.
Thread.interupted() is true if the current thread has been interrupted. Either way, the code breaks out of the loop and the nag method returns.