sys用户必须使用sysdba或者sysoper的身份才能登陆。  
  如果你使用DBA Studio登陆的话，你能看到在用户名，密码下面有一个选择框，默认是Normal；但可以从这里选择sysdba或者sysoper。  
   
  JDBC我还不知道怎么改变登陆身份。  
  你换用别的用户登陆试一下吧。  
  一般程序中用system/manager就行了。
不要用sys连接oralce，用sys新建一个用户测试
public class DBCon {
    private static String driver = "oracle.jdbc.driver.OracleDriver";
    private static String url = "jdbc:oracle:thin:@127.0.0.1:1521:orcl";
    private static String user = "scott";
    private static String password = "tiger";
   
    public static Connection getConnection(){
        try {
            Class.forName(driver);
            Connection con=DriverManager.getConnection(url, user, password);
            System.out.println("ok");
            return con;
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return null;
    }
   
    public static void close(Connection con,Statement stm,ResultSet rs){
        if(con!=null){
            try {
                con.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(stm!=null){
            try {
                stm.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        if(rs!=null){
            try {
                rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
    }
   
    public static void main(String[] args) {
        DBCon.getConnection();
    }}