Introduction to Multithreading

Multithreading is a programming concept that allows a program to execute multiple threads concurrently. A thread is a lightweight process, and multithreading enables concurrent execution of different parts of a program, improving performance and responsiveness. In Java, multithreading is supported by the `java.lang.Thread` class and the `java.util.concurrent` package. Let's explore the basics of multithreading in Java:

1. Creating Threads

In Java, you can create a thread by extending the `Thread` class or implementing the `Runnable` interface.

Extending the Thread class

class MyThread extends Thread {
    public void run() {
        // Code to be executed by the thread
        System.out.println("Thread running.");
    }
}

public class Main {
    public static void main(String[] args) {
        MyThread thread = new MyThread();
        thread.start(); // Start the thread
    }
}

Implementing the Runnable interface

class MyRunnable implements Runnable {
    public void run() {
        // Code to be executed by the thread
        System.out.println("Thread running.");
    }
}

public class Main {
    public static void main(String[] args) {
        MyRunnable myRunnable = new MyRunnable();
        Thread thread = new Thread(myRunnable);
        thread.start(); // Start the thread
    }
}

2. Thread States

- New: A thread that has been created but has not yet started.

- Runnable: A thread that is ready to run is moved to the runnable state.

- Blocked/Waiting: A thread that is waiting for a resource (e.g., I/O operation) or waiting for another thread to release a lock.

- Timed Waiting: A thread that is waiting for a specific amount of time.

- Terminated: A thread that has exited or terminated its execution.

3. Thread Lifecycle

- New: A thread is in this state when it's instantiated but hasn't yet started its execution.

- Runnable: The thread is ready to run, and it's waiting for the CPU to execute its task. It can transition to this state from the "New" state or when it comes out of the "Blocked" or "Waiting" state.

- Blocked/Waiting: The thread is temporarily inactive because it's waiting for a resource, such as I/O operations, or waiting for another thread to release a lock. It can transition back to the "Runnable" state when the required resource becomes available.

- Timed Waiting: Similar to the "Blocked/Waiting" state, but the thread is waiting for a specific amount of time.

- Terminated: The thread has completed its execution or was terminated prematurely. Once a thread enters this state, it cannot transition to any other state.

4. Thread Synchronization

Thread synchronization is the process of controlling the access to shared resources by multiple threads to avoid data inconsistency and thread interference. In Java, you can use `synchronized` blocks or methods, or use higher-level concurrency utilities like `Lock` and `Semaphore` for synchronization.

5. Thread Communication

Thread communication allows threads to cooperate and synchronize their actions. In Java, you can use methods like `wait()`, `notify()`, and `notifyAll()` to coordinate the execution of threads.

Conclusion

Multithreading in Java allows you to write concurrent programs that can perform multiple tasks simultaneously, improving performance and responsiveness. Understanding the basics of creating threads, managing their lifecycle, synchronization, and communication is essential for developing efficient multithreaded applications in Java.