Problem with creating JAVA Source. please help

Question

Dear all
how are you.
In fact I have made a simple java class that return a string which represents the screen size . for example 800/600 or 1024/768 or others
but I face error ORA-29541 class string.string could not be resolved
This what i made
first i created my JAVA Source
CREATE OR REPLACE AND RESOLVE JAVA SOURCE NAMED "ScreenProperty" AS
import java.lang.Object;
import java.awt.*;
public class ScreenProperty
int w;
int h;
public static String getScreenSize()
w = Toolkit.getDefaultToolkit().getScreenSize().width;
h = Toolkit.getDefaultToolkit().getScreenSize().height;
return w+"/"+h;
SQL>Operation 160 succeeded.
this means the the java source created successfuly
and I'm sure that my java code is correct
then i created a fuction to call this java source as fellow
SQL> create or replace function f_get_screen_size
return varchar2
as language java
name 'ScreenProperty.getScreenSize() return java.lang.String';
Function created.
the I Issued this sql statement to return the result that should be varchar2 that represent the sceen size(1024/768)
SQL> select f_get_screen_size from dual;
ORA-29541 class string.string could not be resolved.
I do not know what is the reason for this error
and when i searched the documentation for this error i found
ORA-29541 class string.string could not be resolved
Cause: An attempt was made to execute a method in a Java class that had not been previously and cannot now be compiled or resolved successfully.
Action: Adjust the call or make the class resolvable
I need to know what is the problem.
And is there another way to load this class other than making JAVA SOURCE
please help

Answer 1

before drawing hands of clock you could fill a circle/oval with certain color, then you'd have that kind of circle that has been filled as backgound.
you may change those dots to be small lines for 12, 3, 6 and 6 o'clock and then have small dots represent 1, 2, 4, 5, 7, 8, 10 and 11 o'clock
anyhow, you should study that code and see how you can modify it whitout breaking it but having it look different.
better yet would be trying to understand how it works, what any line there means and then recreate your own... this way you would learn more....
and if there are some methods or anything you don't understand, then look them up from API documentation
good luck.