Java · Theory

Calling run() method

Theory

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Calling run() method

Calling run() method is part of Java concurrency. A thread is a path of work inside a process. Create with Thread or Runnable, then call start() — not run(). run() only runs on the same thread.

For Calling run() method: if two threads share data, synchronize or the result can be wrong. sleep pauses. join waits for another thread to finish. daemon threads die when all user threads finish.

Calling run() method deadlock: two threads wait for each other’s lock forever. Avoid by locking in the same order. Don’t guess thread order — it can change every run.

Let's take this on the board with one tiny Main class — no extra files. Calling run() method — start() schedules the thread; main also prints — order may vary. Start from main, go line by line, and stop at each print. That output is the proof for Calling run() method.

Exam tip

start() vs run() is a classic interview question.

Example

// Thread demo
public class Main {
  public static void main(String[] args) {
    Thread t = new Thread(() -> System.out.println("Hi from thread"));
    t.start();
    System.out.println("Hi from main");
  }
}

Calling run() method — start() schedules the thread; main also prints — order may vary.

Short notes

DefCalling run() method — thread = one path of work. start() schedules it. run() does not.
RuleCalling run() method — shared data needs synchronization.
RememberCalling run() method — sleep = pause. join = wait for other thread.
TrapCalling run() method — calling run() instead of start(). Deadlock = locks in wrong order.

// Thread demo public class Main { public static void main(String[] args) { Thread t = new Thread(() -> System.out.println("Hi from thread")); t.start(); System.out.println("Hi from main"); } }

Calling run() method

Example

Short notes

Questions

Calling run() method

Example

Short notes

Questions