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1. start() vs run()
Output:
Calling run()
Running in: main
Calling start()
Running in: Thread-2
When run() is called directly, it runs like a normal method, so it is executed by the main thread.
When start() is called, Java creates a new thread, and then the run() method runs inside that new thread. That is why the second output shows Thread-2.
So, run() does not start a new thread, but start() does.
2. Daemon Threads
The output is not always the same. The main thread prints:
Main thread ends.
and then finishes. Since the created thread is marked as a daemon thread using setDaemon(true), the JVM does not wait for it to complete. As a result, the program may stop before the daemon thread finishes all 20 iterations. Depending on the scheduling, the message
Daemon thread running...
may appear a few times or may not appear at all.
If setDaemon(true) is removed, the thread becomes a normal user thread. In that case, the JVM waits for the thread to finish, and the message
Daemon thread running...
will be printed 20 times before the program exits.
Daemon threads are commonly used for background tasks such as logging, monitoring, and cleanup operations.
3. A shorter way to create threads
Output:
Thread is running using a ...!
The syntax () -> { ... } is called a lambda expression.
It is a shorter way to write a Runnable. Instead of creating a separate class or anonymous class, we write the thread task directly inside the Thread constructor.
This makes the code shorter and easier to read.