Example:

class Demo
{ 
	void print(int n)
	{
		synchronized(this)   // synchronized block            
		{                                                                               
			for(int i=1;i<=3;i++)
			{
				System.out.println(n*i);
				try
				{
					Thread.sleep(500);
				}
				catch(Exception e)
				{
					System.out.println(e);
				}
			}
		}
	} 
}
class MyThread1 extends Thread
{
	Demo d;
	MyThread1(Demo d)
	{
		this.d=d; 
	}
	public void run()
	{
		d.print(5);
	}
}
class MyThread2 extends Thread
{ 
	Demo d;
	MyThread2(Demo d)
	{
		this.d=d; 
	} 
	public void run()
	{
		d.print(10); 
	} 
}
public class SynchronizationExa2
{
	public static void main(String args[])
	{
		Demo obj = new Demo();                        
		MyThread1 obj1=new MyThread1(obj);
		MyThread2 obj2=new MyThread2(obj);
		obj1.start();
		obj2.start();
	}
}