Synchronized block in Multithreading

sync2.java

/*synchronized means only thread has access to it at a time */
import java.io.*;

class Routine
{
	private String msg;
	Routine(String msg)
	{
		this.msg = msg;
	}
	public void display() 
	{
		System.out.print("[ ");
		try
		{
			Thread.sleep(1000);
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
		System.out.print(msg);
		try
		{
			Thread.sleep(1000);
		}
		catch(Exception e)
		{
			e.printStackTrace();
		}
		System.out.println(" ]");
	}
}

class MyThread implements Runnable
{
	private Routine ob;
	MyThread(Routine ob)
	{
		this.ob = ob;
	}
	@Override
	public void run()
	{
		synchronized(ob)/* If this is not synchronized, output is very random */
		{
			System.out.println("Thread started");
			ob.display();
		}
	}
}

public class test2
{
	public static void main(String[] args)
	{
		Routine obj = new Routine("Hi");
		Thread t1 = new Thread(new MyThread(obj));
		Thread t2 = new Thread(new MyThread(obj));
		Thread t3 = new Thread(new MyThread(obj));
		t1.start();
		t2.start();
		t3.start();
	}
}