CREATE OR REPLACE JAVA SOURCE NAMED "Fokke" 

AS
       
   public class Hello 
   {                                                          
      public static String hello() 
      {
      
         return "Hello World";

      }
   }
   ;
/

This will create 2 db objects:

The JAVA SOURCE object will be stored as plain text (the java source code) and 
   the JAVA CLASS will be stored as the compiled java code.

[jav@db1.ben.nl] SELECT object_name, object_type FROM user_objects;

OBJECT_NAME                         OBJECT_TYPE
---------------------------------------------------
Fokke                               JAVA SOURCE
Hello                               JAVA CLASS

Create a wrapper, callspec clause:

CREATE OR REPLACE FUNCTION call_Fokke 
   RETURN VARCHAR2
   AS 
   LANGUAGE JAVA 
       NAME 'Hello.hello() return java.lang.String'
   ;
/

SELECT call_Fokke FROM DUAL;