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();
  }
}