Main Thread:

When we run a Java program  then main thread begins running immediately. It is created automatically. The main thread is the first as well as last thread in a java program to end.

It is the main thread from which other child threads will be created.

Example:

// the main Thread. 
public class MainThread {
  public static void main(String args[]) {
    Thread t = Thread.currentThread();
    System.out.println("Current thread: " + t);
    // change the name of the thread
    t.setName("My Thread");
    System.out.println("After name change: " + t);
    try {
      for (int n = 5; n > 0; n--) {
        System.out.println(n);
        Thread.sleep(1000);
      }
    } catch (InterruptedException e) {
      System.out.println("Main thread interrupted");
    }
  }
}

Output:

Current thread: Thread[main,5,main]
After name change: Thread[My Thread,5,main]

5
4
3
2
1

We can control main thread by using  thread object. Thread object will hold the reference of the main thread with the help of currentThread() method of  Thread class.