Oracle SQLJ "ORA-29531 - no method ... in class ..."

Today, my colleague ask me to check one SQLJ error, "ORA-29531 - no method ... in class ...", all of right and the object status is valid, why still have the error? check the Oracle SQLJ Frequently Asked Questions,we found the root cause, when we define the "String" at java, it's java.lang.String, we need declare this at oracle procedure, otherwise it will use "java.sql.String", then raise the error.