How to Write, Use, and Test a Singleton Class

class Mysingleton{ private Mysingleton objsingleton = null; private Mysingleton() { } //single way to get its instance. public Mysingleton getInstance() {    if(objsingleton == null)    {      objsingleton = new Mysingleton();    }    return objsingleton; } public Connection dbconnectivity() {  //some connectivity code   .... }}public class Testclass{  public void callSingleton()  {    Mysingleton singobj = Mysingleton.getInstance();    singobj.dbconnectivity();  }  public static void main(String args[])  {    Testclass obj = new Testclass();    obj.callSingleton();  }}