public class A

 {

     public static int  abc = ;

     public int  uns=；

     private static A instance_;

         public static A instance{

             get{

                 return instance_;

             }

         }

         static A(){

             instance_ = new A();

              abc= ;//静态成员可以直接赋值

             instance_.uns=;//正确

             //uns=2;会报错，非静态成员要通过类实例调用

         }

 }                              

 public class A{

         private static A instance_;

         public static A instance{

             get{

                 if(instance_ = null)

                     instance_ = new A();

                 return instance_;

             }

         }

 }