C:UsersAdministrator>copy con Hello.java
public class Hello
{
    public static String world()
    {
    return "Hello World";
    }
}
^Z
        1 file(s) copied.

C:UsersAdministrator>type Hello.java
public class Hello
{
    public static String world()
    {
    return "Hello World";
    }
}

C:UsersAdministrator>set JAVA_HOME=O:oraclebaseproduct12.2.0dbhome_1jdk

C:UsersAdministrator>set PATH=%JAVA_HOME%bin;%PATH%

C:UsersAdministrator>javac Hello.java

C:UsersAdministrator>jar cvf Hello.jar Hello.class
added manifest
adding: Hello.class(in = 273) (out= 209)(deflated 23%)

C:UsersAdministrator>sqlplus / as sysdba

SQL*Plus: Release 12.2.0.1.0 Production on Fri Nov 9 16:18:34 2018

Copyright (c) 1982, 2016, Oracle.  All rights reserved.


Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> alter session set container=pdb1;

Session altered.

SQL> exec dbms_java.loadjava('C:UsersAdministratorHello.jar');

PL/SQL procedure successfully completed.

SQL> select owner, object_name, object_type, status, created
     from dba_objects where object_name = 'Hello';

OWNER      OBJECT_NAM OBJECT_TYPE             STATUS  CREATED
---------- ---------- ----------------------- ------- ---------
SYS        Hello      JAVA CLASS              INVALID 09-NOV-18

SQL> alter java class "Hello" compile;

Java altered.

SQL> select owner, object_name, object_type, status, created
     from dba_objects where object_name = 'Hello';

OWNER      OBJECT_NAM OBJECT_TYPE             STATUS  CREATED
---------- ---------- ----------------------- ------- ---------
SYS        Hello      JAVA CLASS              VALID   09-NOV-18

SQL> drop java class "Hello";

Java dropped.