/**
 * A test for SingletonA
 */
public class TestA {
 public static void main(String[] args) {
 // Can not create a instance !
 //SingletonA instance1 = new SingletonA(); 
 SingletonA instance2 = SingletonA.getInstance();
 if(instance2 != null) {
 instance2.setNum();
 System.out.println("i is:" + instance2.getNum());
 }
 SingletonA instance3 = SingletonA.getInstance();
 if(instance3 == null) {
 System.out.println("Can not get instance twice !"); 
 }
 }
}