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Thread Pool in Java

Theory

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Thread Pool in Java

Thread Pool 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 Thread Pool: 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.

Thread Pool 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. Thread Pool in Java — 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 Thread Pool.

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");
  }
}

Thread Pool in Java — start() schedules the thread; main also prints — order may vary.

Short notes

DefThread Pool — thread = one path of work. start() schedules it. run() does not.
RuleThread Pool — shared data needs synchronization.
RememberThread Pool — sleep = pause. join = wait for other thread.
TrapThread Pool — 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"); } }

Thread Pool in Java

Example

Short notes

Questions

Thread Pool in Java

Example

Short notes

Questions