Question

This is a small part of the application where user can register any number of employees and employee id is generated by using a while loop….As i close the application & start filling the data again in second round…the value of employee id empid resets to zero. Well, as long as the application is running, i get the desired o/p i.e. a unique id is allotted to every employee. I dont want empid‘s value to start from 0 whenever i start the application. Need alternatives and/or any modification. Code is provided here

int empcount=0;
    public void actionPerformed(ActionEvent ae) {
            //---------------------If user wants to add data
            if(ae.getActionCommand()=="ADD EMPLOYEE") {
                System.out.println("ADDING");
        try{
            empcount=empcount+1;//----------------will assign employees with unique emp id
            //--------------------returns the text in name field to variables 
            String s_name=name.getText();
            int s_code=empcount;
            String s_dept=dept.getText();
            String s_ph=ph.getText();
            String s_bg=bg.getText();
            String s_add=add.getText();
            String s_date=date.getText();
            PreparedStatement st=null;
            Connection con = null;
            Class.forName("org.hsqldb.jdbcDriver");
            con = DriverManager.getConnection("jdbc:hsqldb:hsql://localhost/", "SA", "");
            st=con.prepareStatement("Insert into EmpReg (emp_name,emp_code,emp_ph,emp_bg,emp_add,emp_date,b_id) values(?,?,?,?,?,?,?)");
            //---------------------parameters and respective values, passed to the SQL statement
            st.setString(1,s_name);
            st.setInt(2,s_code);
            st.setString(3,s_ph);
            st.setString(4,s_bg);
            st.setString(5,s_add);
            st.setString(6,s_date);
            st.setString(7,s_dept);
            st.execute();
            JOptionPane.showMessageDialog(null,"Data is inserted into the database");
            JOptionPane.showMessageDialog(code, "employee code"+ empcount+"");
            con.close();
        }
            catch(Exception Ee){
            System.out.println(Ee);
            }
                }       
            }
        });

Answer 1

The standard SQL way of doing this, is having an “autoincrement” primary key (emp_code), for hsqldb see IDENTITY.
In the SQL INSERT statement leave out the primary key. Now the database generates a unique new key.
After the execution, you can retrieve the generated primary key from the statement with getGeneratedKeys.

This ensures that two parallel processes will not mess up the primary keys.