Understanding the Thread Class and Its Methods in Java

Introduction

Java provides built-in support for multithreading through the Thread class, which allows developers to execute multiple tasks concurrently. Understanding the Thread class and its methods is essential for efficient and scalable Java applications.

In this article, we will explore the Thread class, its important methods, and practical examples to help Java professionals master multithreading.

What is the Thread Class in Java?

The Thread class in Java belongs to the java.lang package and is used to create and manage threads. It extends the Object class and implements the Runnable interface, allowing developers to define and execute independent execution paths.

Creating a Thread in Java

There are two main ways to create a thread in Java:

Extending the Thread class
Implementing the Runnable interface

1. Extending the `Thread` Class

class MyThread extends Thread {
    public void run() {
        System.out.println("Thread is running...");
    }
    
    public static void main(String[] args) {
        MyThread t1 = new MyThread();
        t1.start();
    }
}

2. Implementing the `Runnable` Interface

class MyRunnable implements Runnable {
    public void run() {
        System.out.println("Thread is running...");
    }
    
    public static void main(String[] args) {
        Thread t1 = new Thread(new MyRunnable());
        t1.start();
    }
}

Important Methods of the Thread Class

1. `start()`

This method starts the execution of the thread by calling the run() method.

Thread t = new Thread(new MyRunnable());
t.start();

2. `run()`

Defines the code that constitutes the thread’s task. It must be overridden in a subclass.

3. `sleep(long milliseconds)`

Pauses the thread for a specified time.

try {
    Thread.sleep(1000);
} catch (InterruptedException e) {
    e.printStackTrace();
}

4. `join()`

Makes the current thread wait until the specified thread finishes execution.

Thread t1 = new Thread(() -> {
    for (int i = 0; i < 5; i++) {
        System.out.println("Thread 1 - " + i);
    }
});
t1.start();
t1.join();

5. `isAlive()`

Checks whether a thread is still running.

if (t1.isAlive()) {
    System.out.println("Thread is still running");
}

6. `yield()`

Pauses the current thread and allows other threads of the same priority to execute.

Thread.yield();

7. `setName(String name)` and `getName()`

Sets and retrieves the name of a thread.

Thread t = new Thread();
t.setName("MyThread");
System.out.println(t.getName());

8. `setPriority(int priority)` and `getPriority()`

Sets and retrieves the priority of a thread.

t.setPriority(Thread.MAX_PRIORITY);
System.out.println(t.getPriority());

9. `interrupt()`

Interrupts a sleeping or waiting thread.

t.interrupt();

10. `daemonThread()`

Marks a thread as a daemon thread.

t.setDaemon(true);

Practical Example of Multithreading

class MultiThreadDemo extends Thread {
    public void run() {
        for (int i = 0; i < 5; i++) {
            System.out.println(Thread.currentThread().getName() + " - " + i);
        }
    }
    
    public static void main(String[] args) {
        MultiThreadDemo t1 = new MultiThreadDemo();
        MultiThreadDemo t2 = new MultiThreadDemo();
        
        t1.setName("Thread 1");
        t2.setName("Thread 2");
        
        t1.start();
        t2.start();
    }
}

External Links

FAQs

1. What is the difference between `start()` and `run()` methods in Java?

The start() method creates a new thread and invokes the run() method, whereas calling run() directly executes the code in the main thread.

2. Can we start a thread twice in Java?

No, once a thread has been started, it cannot be restarted.

3. What is the purpose of the `yield()` method?

yield() allows other threads of the same priority to execute before resuming.

4. What happens if the `run()` method is not overridden?

The default implementation of run() does nothing, and the thread will not execute any task.

5. What is a daemon thread?

Daemon threads run in the background and do not prevent the JVM from exiting.

6. How do you stop a running thread in Java?

The interrupt() method is used to request a thread to stop.

7. How does `sleep()` differ from `wait()`?

sleep() pauses the thread for a specified time, while wait() makes a thread wait until notified.

8. What is thread priority in Java?

Thread priority determines the execution preference of threads but does not guarantee execution order.

9. Can multiple threads run concurrently in Java?

Yes, Java supports multithreading to run multiple tasks in parallel.

10. What is the difference between `synchronized` and `volatile`?

synchronized ensures mutual exclusion, while volatile guarantees visibility of changes across threads.

Mastering the Thread class and its methods is crucial for Java professionals working on concurrent programming. By leveraging these features, developers can create efficient, responsive, and scalable applications.

Introduction

What is the Thread Class in Java?

Creating a Thread in Java

1. Extending the Thread Class

2. Implementing the Runnable Interface

Important Methods of the Thread Class

1. start()

2. run()

3. sleep(long milliseconds)

4. join()

5. isAlive()

6. yield()

7. setName(String name) and getName()

8. setPriority(int priority) and getPriority()

9. interrupt()

10. daemonThread()