1: 
        the output is Calling run()
        Running in: main
        Calling start()
        Running in: Thread-2

t1.run() does not start a new thread. 
It just calls the run() method like a normal method call, and it executes on the current thread.
t2.start() creates a new thread and then that new thread executes run(), so current Thread Name becomes Thread-2.

run() is just a normal method call, so it runs in the current thread.

start() creates a new thread, and that new thread executes run().

2:
        Output:
                Main thread ends.
                It may also print:
                Daemon thread running…
                a few times, or sometimes not at all.
        Why:
                Because the created thread is a daemon thread. Daemon threads run in the background, and when the main thread finishes, the JVM can stop immediately. 
                So the daemon thread may not complete its loop.
        If thread.setDaemon(true) is removed:
                Then the thread becomes a user thread (non-daemon thread).
                and the JVM will wait for it to finish, so "Daemon thread running..." will print many times until the loops end.
        Real-life uses of daemon threads:
                Garbage collection
                Background auto-save
                Cache cleanup
                Monitoring or logging services
                Timer or scheduler tasks running in background
3:
        What output do you get from the program?
                Thread is running using a …!
        What is the () -> { ... } syntax called?
                This is called a lambda expression.
        
        How is this code different from creating a class that extends Thread or implements Runnable?
                This is a shorter and cleaner way to write thread code. 
                Instead of creating a separate class, the task is written directly inside the lambda expression.