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Introduction to Multithreading in Java

Introduction​

Multithreading is a powerful feature in Java that allows concurrent execution of two or more threads, which can significantly enhance the performance of your applications; this capability is particularly beneficial when dealing with tasks that can be performed in parallel, such as handling multiple user requests in a server application or performing complex calculations in the background without freezing the user interface.

1. Understanding Threads​

A thread, in the context of Java programming, is the smallest unit of a process that can be scheduled for execution; it shares the process resources, including memory and open files, but executes independently, which means multiple threads can exist within the same application, executing simultaneously and potentially interacting with one another.

2. Creating Threads​

Implementing the Runnable Interface​

One of the most common ways to create a thread in Java is by implementing the Runnable interface, which requires you to define the run method; this method contains the code that constitutes the new thread’s task.

public class MyRunnable implements Runnable {
    @Override
    public void run() {
        System.out.println("Thread is running");
    }

    public static void main(String[] args) {
        Thread thread = new Thread(new MyRunnable());
        thread.start();
    }
}

Extending the Thread Class​

Alternatively, you can create a thread by extending the Thread class itself, which allows you to directly override the run method; however, this approach is less flexible compared to implementing Runnable, as Java does not support multiple inheritance.

public class MyThread extends Thread {
    @Override
    public void run() {
        System.out.println("Thread is running");
    }

    public static void main(String[] args) {
        MyThread thread = new MyThread();
        thread.start();
    }
}

3. Thread Lifecycle​

Understanding the lifecycle of a thread is crucial for effective multithreading; a thread in Java can be in one of several states, including New, Runnable, Blocked, Waiting, Timed Waiting, and Terminated. Each of these states represents a distinct phase in the thread’s execution process.

New​

When a thread is first created, it is in the New state, meaning it has been instantiated but not yet started.

Runnable​

Once the thread’s start method is called, it enters the Runnable state; it is now ready to run and is waiting for the thread scheduler to allocate CPU time.

Blocked​

A thread enters the Blocked state when it is waiting for a monitor lock to enter or re-enter a synchronized block or method.

Waiting​

A thread is in the Waiting state when it is waiting indefinitely for another thread to perform a particular action.

Timed Waiting​

This state is similar to Waiting, but it has a specified waiting time; for instance, a thread can enter this state when it calls sleep or join with a timeout.

Terminated​

After a thread has completed its execution, it enters the Terminated state; the thread has now finished running, and it cannot be restarted.

4. Synchronization​

In a multithreaded environment, multiple threads can access shared resources, which can lead to inconsistent data if not managed properly; synchronization is the mechanism that ensures that only one thread can access a resource at a time, thereby preventing data corruption and ensuring thread safety.

Synchronized Methods​

You can synchronize a method by using the synchronized keyword; this ensures that only one thread can execute the method at a time on the same object.

public synchronized void synchronizedMethod() {
    // critical section
}

Synchronized Blocks​

For more fine-grained control, you can use synchronized blocks, which allow you to synchronize a specific section of code rather than the entire method.

public void method() {
    synchronized(this) {
        // critical section
    }
}

Conclusion​

Multithreading in Java is a complex yet incredibly powerful feature that allows for the concurrent execution of tasks, which can significantly improve the performance and responsiveness of your applications; understanding how to create, manage, and synchronize threads is essential for developing robust multithreaded applications. By leveraging the capabilities of multithreading, you can build applications that efficiently utilize system resources and provide a better user experience.