SQL> create or replace and compile java source named "MyClass" as
  2  public class MyClass {
  3    public static int facto(int n) {
  4      if (n <= 1) {
  5        return 1;
  6      }
  7      return n * facto(n-1);
  8    }
  9  };
 10  /

Java created.

SQL> 
SQL> create or replace function facto_java(n in number) return number as
  2  Language java
  3  name 'MyClass.facto(java.lang.Number) return java.lang.Number';
  4  /

Function created.

SQL> 
SQL> select facto_java(5) from dual;
select facto_java(5) from dual
*
ERROR at line 1:
ORA-29531: no method facto in class MyClass 

[oracle@localhost ~]$ oerr ora 29531
29531, 00000, "no method %s in class %s"
// *Cause: An attempt was made to execute a non-existent method in a
//          Java class.
// *Action: Adjust the call or create the specified method.
[oracle@localhost ~]$ 

SQL> create or replace and compile java source named "MyClass" as
  2  import java.sql.*;
  3  public class MyClass {
  4    public static int facto(int n) {
  5      if (n <= 1) {
  6        return 1;
  7      }
  8      return n * facto(n-1);
  9    }
 10  };
 11  /

Java created.

SQL> create or replace function facto_java(n in number) return number as
  2  Language java
  3  name 'MyClass.facto(java.lang.Number) return java.lang.Number';
  4  /

Function created.

SQL> select facto_java(5) from dual
  2  /
select facto_java(5) from dual
                          *
ERROR at line 1:
ORA-29531: no method facto in class MyClass


SQL> create or replace function facto_java(n in number) return number as
  2  Language java
  3  name 'MyClass.facto(int) return int';
  4  /

Function created.

SQL> select facto_java(5) from dual
  2  /

FACTO_JAVA(5)
-------------
          120

SQL>  

create or replace and compile java source named "MyClass" as
import java.sql.*;
public class MyClass {
  public static int facto(int n) {
    if (n <= 2) {
      return n;
    }
    return n * facto(n-1);
  }
};
/

if (n <= 2)

import java.sql.*;