《thinking in java》 接口与内部类

书本上的例子

改编后的。

 package test2;

 class A{
     interface B{void f();}
     public class BImp implements B{public void f(){}}
     private class BImp2 implements B{public void f(){}}

     public interface C{void f();}
     class CImp implements C{public void f(){}}
     private class CImp2 implements C{public void f(){}}

     private interface D{void f();}
     private class DImp implements D{public void f(){}}
     public class DImp2 implements D{public void f(){}}

     public D getD(){return new DImp2();}
     private D dRef;
     public void receiveD(D d){dRef=d;dRef.f();}    

 }
 interface E{
     interface G{void f();}

     public interface H{void f();}
     void g();
 }
 public class NestingInterfaces {

     public class BImp implements A.B{public void f(){}}
     class CImp implements A.C{public void f(){}}

 //    The type A.D is not visible
 //    class DImp implements A.D{public void f(){}}

     class EImp implements E{public void g(){}}
     class EGimp implements E.G{public void f(){}}

     class EImp2 implements E{
         public void g(){}
         class EG implements E.G{public void f(){}}
     }

     public static void main(String[] args) {
         A a=new A();

         //编译器在A.D处报错：The type A.D is not visible
 //        A.D ad=a.getD();

         //编译器在 a.getD() 处报错：Type mismatch: cannot convert from A.D to A.DImp2
 //        A.DImp2 di2=a.getD();  

         A.DImp2 di2=(A.DImp2)a.getD();
         System.out.println(di2.getClass().getName());//test2.A$DImp2

         //The type A.D is not visible
 //        a.getD().f();

         ((A.DImp2)a.getD()).f();

         A a2=new A();
         a2.receiveD(a.getD());
     }

 }

可以顺利运行。

PS：编译器识别代码总是从左到右，从上到下，一步步进行的。至于代码的运行逻辑，那是识别之后的事情。