checking if variable is blank after 20 seconds

[Pouncer]

public class Test {
    public static void main(String[] args) {
	long startTime = System.nanoTime();
	
	String blah = "";

	while(true) {
	    System.out.println("testing");
	    if (System.nanoTime() - startTime > 20000)
		break;
	}
    }   
}

i want to somehow check if blah.equals("") after 20 seconds, can anyone help me?