PLS-00103: encountered the symbol ", " when expecting

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Java

create or replace function sum
   (n1 in number,n2 in number)
   return number
   is
   temp number(8);
   begin
   temp :=n1+n2;
   return temp;
   end;
   /

Error :
java.sql.SQLException: ORA-06550: line 1, column 19:
PLS-00103: Encountered the symbol "," when expecting one of the following:

. ( ) * @ % & - + / at mod remainder rem <an exponent="" (**)="">
|| indicator multiset

What I have tried:

import java.sql.*;

class CallableStatementFunction	
{
	public static void main(String args[])throws Exception
	{
		try
		{
			Class.forName("oracle.jdbc.driver.OracleDriver");
			Connection con=DriverManager.getConnection(".....");
			
			CallableStatement cs=con.prepareCall("{?= call sum(?,?)}");  
			
			cs.setInt(2,10);  
			cs.setInt(3,20);
			cs.registerOutParameter(1,Types.INTEGER); 
			cs.execute();    
			
			System.out.println("10+20 =" + cs.getInt(1));
      			
			cs.close();		
			con.close();
		}
		catch(Exception e)
		{
			System.out.println(e);
		}
	}
}