import java.sql.*;
    class OracleCon {
    public static void main(String args[]) {
       try {
        //step1 load the driver class
           Class.forName("oracle.jdbc.driver.OracleDriver");
        //step2 create the connection object
           Connection con= DriverManager.getConnection ("jdbc:oracle:thin:@localhost:1521:xe","hr","hr");
        //step3 create the statement object
           Statement stmt = con.createStatement();
           ResultSet rs = stmt.executeQuery("select * from departments");
          while (rs.next()) {
            String dname = rs.getString("DEPARTMENT_NAME");
            System.out.println(dname);
          }

      Statement stmt1 = con.createStatement();
      ResultSet rs1 = stmt1.executeQuery("select * from employees");
      while (rs1.next()) {
         Integer eno = rs1.getInt("employee_id");
         System.out.println(eno);

      }
       con.close();
     } catch (Exception e) {
         System.out.println(e);

     }
   }
}

String sql = "select e.* from employee e,  department d where d.department_name = ? and d.department_name=e.deparment.name"); )// ? will be replaced by a parameter obtained from a user

PreparedStatement stmt = con.prepareStatement(sql);

stmt.setString(1, deptName); //deptName is obtained from the user

ResultSet rs = stmt.executeQuery();
.....