Java Program to Create a Thread

Thread can be referred to as a lightweight process. Thread uses fewer resources to create and exist in the process; thread shares process resources. The main thread of Java is the thread that is started when the program starts. The slave thread is created as a result of the main thread. This is the last thread to complete execution.

 A thread can programmatically be created by:

1. Implementing the java.lang.Runnable interface.
2. Extending the java.lang.Thread class.

You can create threads by implementing the runnable interface and overriding the run() method. Then, you can create a thread object and call the start() method.

Thread Class:

The Thread class provides constructors and methods for creating and operating on threads. The thread extends the Object and implements the Runnable interface.

// start a newly created thread.
// Thread moves from new state to runnable state
// When it gets a chance, executes the target run() method
public void start()  

Runnable interface:

Any class with instances that are intended to be executed by a thread should implement the Runnable interface. The Runnable interface has only one method, which is called run().

// Thread action is performed
public void run() 

Benefits of creating threads :

• When compared to processes, Java Threads are more lightweight; it takes less time and resources to create a thread.
• Threads share the data and code of their parent process.
• Thread communication is simpler than process communication.
• Context switching between threads is usually cheaper than switching between processes.

Calling run() instead of start()

The common mistake is starting a thread using run() instead of start() method. 

  Thread myThread = new Thread(MyRunnable());
  myThread.run();  //should be start();

The run() method is not called by the thread you created. Instead, it is called by the thread that created the myThread. 

Example 1: By using Thread Class

Java

import java.io.*;
class GFG extends Thread {
    public void run()
    {
        System.out.print("Welcome to GeeksforGeeks.");
    }
    public static void main(String[] args)
    {
        GFG g = new GFG(); // creating thread
        g.start(); // starting thread
    }
}

Output

Welcome to GeeksforGeeks.

Example 2: By implementing Runnable interface

Java

import java.io.*;
class GFG implements Runnable {
    public static void main(String args[])
    {
        // create an object of Runnable target
        GFG gfg = new GFG();

        // pass the runnable reference to Thread
        Thread t = new Thread(gfg, "gfg");

        // start the thread
        t.start();

        // get the name of the thread
        System.out.println(t.getName());
    }
    @Override public void run()
    {
        System.out.println("Inside run method");
    }
}

Output

gfg
Inside run method