What are differences between Daemon thread and Orphan thread in java?

 In Java, the concepts of daemon threads and orphan threads refer to different aspects of thread management and behavior. Here's a detailed comparison:

Daemon Thread

• Purpose: Daemon threads are designed to provide background services while other non-daemon threads run. They are often used for tasks like garbage collection, background I/O, or other housekeeping activities.
• Lifecycle: Daemon threads do not prevent the JVM from exiting. If all user (non-daemon) threads finish execution, the JVM will exit, and all daemon threads will be terminated, regardless of whether they have completed their tasks.
• Creation: You can create a daemon thread by calling setDaemon(true) on a Thread object before starting it. Example:

  Example:
  Thread daemonThread = new Thread(new RunnableTask());
  daemonThread.setDaemon(true);
  daemonThread.start();

• Usage Consideration: Daemon threads should not be used for tasks that perform critical operations or that must be completed before the application exits.

Orphan Thread

• Definition: The term "orphan thread" is not a standard term in Java threading terminology. However, it generally refers to a thread that continues to run even though its parent thread (the thread that created it) has finished execution.
• Lifecycle: Orphan threads are still considered user threads unless explicitly set as daemon threads. Therefore, they can prevent the JVM from shutting down if they are still running.
• Creation: An orphan thread can be any thread that is created by a parent thread. If the parent thread completes its execution, but the child thread continues to run, the child thread becomes an orphan thread. Example:

  Example:
  Thread parentThread = new Thread(new Runnable() {
      @Override
      public void run() {
          Thread childThread = new Thread(new RunnableTask());
          childThread.start();
          // Parent thread finishes, but child thread continues
      }
  });
  parentThread.start();
  

• Usage Consideration: Orphan threads are normal user threads, so they need to be managed properly to ensure that they don't cause the application to hang by keeping the JVM alive indefinitely.

Key Differences

1. JVM Exit:
   • Daemon Thread: Does not prevent the JVM from exiting.
   • Orphan Thread: Can prevent the JVM from exiting if it is a user thread.
2. Creation:
   • Daemon Thread: Explicitly created by setting setDaemon(true).
   • Orphan Thread: Any child thread that outlives its parent thread.
3. Use Case:
   • Daemon Thread: Used for background tasks.
   • Orphan Thread: Can be any thread continuing to run independently of its parent thread.

Understanding these concepts helps in designing multi-threaded applications where thread lifecycle management is crucial.