124 lines
4.6 KiB
Markdown
124 lines
4.6 KiB
Markdown
## 1 . `start()` vs `run()` :
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```
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public class StartVsRun {
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static class MyRunnable implements Runnable {
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public void run() {
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System.out.println("Running in: " + Thread.currentThread().getName());
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}
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}
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public static void main(String[] args) throws InterruptedException {
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Thread t1 = new Thread(new MyRunnable(), "Thread-1");
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System.out.println("Calling run()");
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t1.run();
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Thread.sleep(100);
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Thread t2 = new Thread(new MyRunnable(), "Thread-2");
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System.out.println("Calling start()");
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t2.start();
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}
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}
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```
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### Questions and Answers:
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* **What output do you get from the program? Why?**
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* ```
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//output:
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Calling run()
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Running in : main
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Calling start()
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Running in : Thread-2
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```
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* *When `t1.run()` is called directly, it executes the `run()` method in the current thread (the main thread), just like a normal method call. No new thread is created. Therefore, `Thread.currentThread().getName()` returns `"main"`.*
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<br>
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* *When `t2.start()` is called, it creates a new thread named `"Thread-2"` and the JVM automatically invokes the `run()` method inside that new thread. Hence, `Thread.currentThread().getName()` returns `"Thread-2"`.*
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<br>
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* **What’s the difference in behavior between calling `start()` and `run()`?**
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<br>
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* *Calling `run()` directly just executes the code inside `run()` in the caller's thread – it's not multithreading.*
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<br>
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* *Calling `start()` schedules the thread to run, and the `run()` method will be executed in a separate thread concurrently.*
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***
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## 2. Daemon Threads :
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```
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public class DaemonExample {
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static class DaemonRunnable implements Runnable {
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public void run() {
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for(int i = 0; i < 20; i++) {
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System.out.println("Daemon thread running...");
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try {
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Thread.sleep(500);
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} catch (InterruptedException e) {
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//[Handling Exception...]
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}
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}
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}
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}
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public static void main(String[] args) {
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Thread thread = new Thread(new DaemonRunnable());
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thread.setDaemon(true);
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thread.start();
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System.out.println("Main thread ends.");
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}
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}
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```
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### Questions and Answers:
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* **What output do you get from the program? Why?**
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* ```
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//output:
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Main thread ends.
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Daemon thread running...
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Daemon thread running...
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...
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//(less than 20 times)
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```
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* *The main thread prints `"Main thread ends."` and then terminates.*
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<br>
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* *The other thread is a `daemon thread`. Daemon threads are background threads that do not prevent the JVM from exiting.*
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<br>
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* *When the last non-daemon thread (in this case, only the main thread) finishes, the JVM terminates immediately without waiting for the daemon thread to complete its loop.*
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<br>
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* *Therefore, the daemon thread only gets to print a few lines before the program shuts down. It never reaches 20 iterations.*
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<br>
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* **What happens if you remove thread.setDaemon(true)?**
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<br>
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* *The thread prints 20 times and then the program ends, because the thread is no longer a daemon (it becomes a regular user thread).*
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* **What are some real-life use cases of daemon threads?**
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<br>
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1. *Background music in a game – While you play, music plays in the background. When you close the game, the music stops immediately. No need to finish the song.*
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<br>
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2. *Auto-save in a text editor – Every few minutes, the program saves your file automatically. If you close the program, it doesn't matter if the auto-save finishes or not. Just stop.*
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<br>
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***
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## 3. A shorter way to create threads :
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```
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public class ThreadDemo {
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public static void main(String[] args) {
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Thread thread = new Thread(() -> {
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System.out.println("Thread is running using a ...!");
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});
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thread.start();
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}
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}
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```
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### Questions and Answers:
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* **What output do you get from the program?**
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* ```
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//output:
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Thread is running using a ...!
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```
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* **What is the `() -> { ... }` syntax called?**
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<br>
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* *It is called a Lambda Expression*
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<br>
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* **How is this code different from creating a class that extends `Thread` or implements `Runnable`?**
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<br>
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* *Shorter and cleaner code.*
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* *No need for a separate class or explicit `run()` override.*
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* *Lambda directly provides the `run()` body.* |