Mastering Threads in Java: Top Interview Questions and Answers



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Mastering Threads in Java Top Interview Questions and Answers

Threads are a fundamental part of the Java programming language and are used to perform concurrent tasks within a Java program. In this article, we'll discuss what threads are, how to create and start them, and how to synchronize them to ensure that critical sections of code are executed correctly.

What are threads?

A thread is a lightweight process that runs concurrently with other threads. Each thread has its own call stack, which is used to store the local variables and method calls for the thread. This allows each thread to have its own execution path, which can be used to perform independent tasks within a Java program.

Creating and starting threads

There are two ways to create a thread in Java: by extending the Thread class or by implementing the Runnable interface.

To create a thread by extending the Thread class, you need to override the run() method, which is used to specify the code that should be executed by the thread. Here's an example of creating a thread by extending the Thread class:
public class MyThread extends Thread {
public void run() {
// code to be executed by this thread
}
}
To create a thread by implementing the Runnable interface, you need to implement the run() method and pass an instance of the Runnable implementation to the Thread constructor. Here's an example of creating a thread by implementing the Runnable interface:

public class MyRunnable implements Runnable {
public void run() {
// code to be executed by this thread
}
}

Thread thread = new Thread(new MyRunnable());
To start a thread, you need to call its start() method. This will create a new thread and execute its run() method. For example:

Thread thread = new MyThread();
thread.start();
Synchronizing threads

When multiple threads are running concurrently, it's important to synchronize their access to shared resources to ensure that critical sections of code are executed correctly. To synchronize threads in Java, you can use the synchronized keyword to block access to a critical section of code. Only one thread can execute the critical section at a time, and other threads that try to enter the critical section are blocked until it is available.

Here's an example of using synchronized to synchronize threads:

public class MyThread extends Thread {
public void run() {
synchronized(this) {
// critical section of code
}
}
}
You can also use the wait(), notify(), and notifyAll() methods to synchronize threads and control their execution. The wait() method can be used to block a thread until it is notified by another thread, while the notify() and notifyAll() methods can be used to wake up threads that are waiting on a particular object.

Conclusion

Threads are an essential part of the Java programming language and are used to perform concurrent tasks within a Java program. By creating and starting threads, and synchronizing their access to shared resources, you can write efficient and scalable Java programs that can take advantage of multiple processors and cores.
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