从数据库加载到jlist会带来错误

Question

I have created a database and every entry from the JList will be added to a table in the database. This work perfectly, but my next task is to get whatever is in the database to load to the JList. I have a function created within the button but it brings up errors. I'm struggling with how to fix this so I hope somebody can resolve it.

Thanks

Here is my code:

JButton btnDb1 = new JButton("J");          
btnDb1.addActionListener(new ActionListener() {                

    public void actionPerformed(ActionEvent arg0) {            
        try {       
            ResultSet rs = st.executeQuery("SELECT * FROM patient");
            while (rs.next()) {
                Patient patient = new Patient(patientname, patientaddress, patientphone, patientid);
                patient.setName(rs.getString("patientname"));
                patient.setAddress(rs.getString("patientaddress"));
                patient.setPhoneNum(rs.getString("patientphone"));
                patient.setID(rs.getInt("patientid"));
                MainDentist.model.addElement(patient);    
            }
        } catch (Exception e) {
            System.out.println(" Error ");                      
        }
    }
});

btnDb1.setBounds(200, 393, 120, 23);
contentPane.add(btnDb1);

Here is my patient class:

public class Patient { 
    public String patientName;
    public String patientAddress;
    public String patientPhone;
    public int patientID;

    public Patient(String patientname, String patientaddress, String patientphone,int patientid){
        patientName = patientname;
        patientAddress = patientaddress;
        patientPhone = patientphone;
        patientID = patientid;
    }

    public String setName(String patientname){            
        return patientName = patientname;
    }

    public String getName(){            
        return patientName;            
    }

    public String setAddress(String patientaddress){            
        return patientAddress = patientaddress;      
    }

    public String getAddress(){            
        return patientAddress;
    }

    public String setPhoneNum(String patientphone){
        return patientPhone = patientphone;
    }

    public String getPhoneNum(){            
        return patientPhone;
    }

    public int setID(int patientid){            
        return patientID = patientid;
    }

    public int getID(){            
        return patientID;            
    }

    public String toString() { // Printing the patient's details to the scroll pane
        return "Patient Name: " + patientName + ", PatientAddress: "
                + patientAddress + ", PatientPhone: " + patientPhone
                + ", patientID: " + patientID +"" ;
    }       
}

Answer 1

Let me rephrase the actionlistener – posting code in comments isn't really helpfull :) First I would put the code from your actionPerformed method somewhere else, best would be even to create some class that handles the whole reading and maybe writing of the database. That way you don't mix reading the database with pushing buttons (maybe you want to create another button that reads the database, too. Then you don't have to write all the code again). Anyway, this is an example:

JButton btnDb1 = new JButton("J");          
btnDb1.addActionListener(new ActionListener() {               

    public void actionPerformed(ActionEvent arg0) {            
        readDatabase();
    }
});

public void onActionPerformed(){
    try { 
        // I don't know where you have that part of code, but you didn't create any statement variable. So here an example DB-connection: 
        String url = "jdbc:mysql://localhost/myDatabase";
        Connection connection = DriverManager.getConnection(url, "username", "password");
        Statement statement = connection.createStatement();      
        ResultSet rs = statement.executeQuery("SELECT * FROM patient");
        while (rs.next()) {
            // read the columns one by one, that way it may be easier to detect errors if one column is wrong
            String name = rs.getString("patientname");
            String address = rs.getString("patientaddress");
            String phone = rs.getString("patientphone");
            int id = rs.getInt("patientid");
            // now that you have all values, create the patient and add it to the model
            // if you have all parameters for the constructor, you don't need to use the setters to set the name and address …
            MainDentist.model.addElement(new Patient(name, address, phone, id));    

        }
    } catch (Exception e) {
        // as JB Nizet suggested, it is easier to detect errors, when you print the whole stack trace (it will tell you in which line the exception gets thrown
        e.printStackTrace();                   
    }        
}

This still may not work right away, if you get errors, edit your post and tell us what goes wrong. BTW: I noticed that you have your variables name , address and all this in the patient set to public . This isn't wrong but it is recommended to use getter and setters (as you do) and make the variables private . That way you can control how the variables get accessed from outside.