从JFrame到Java类获取字符串值

Question

Hello i'm trying to build a small application that will allow me to store email addresses in a MySQL database. What i've done is that i've created a Java Class file ( ec.java ) and a connection that works fine and code for executing this into the database.

In the JFrame ( ecframe.java ) have i created a textfield and a button. When typing in the email address and pressing the button it will store this information to a string called textFieldValue. But what i can't figure out is how to get this string into my ec.java file.

This is my code from ec.java:

package emailcollector;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;


public class ec {

    public static void main(String[] args) {
        try{
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost", "admin", "pass");

            Statement stmt = (Statement) con.createStatement();

            String email = textFieldValue;

            String insert = "INSERT INTO emails VALUES ('" + email + ")";

            stmt.executeUpdate(insert);
        }catch(Exception e) {
    }
    }
}

And this is my code inside the ecframe.java :

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
        String textFieldValue = jTextField1.getText();

        JOptionPane.showMessageDialog(this, "Added: \nEmail: " + textFieldValue);
    } 

Is this because of the "private". It's confusing for me. Thanks in advance!

Answer 1

make con static variable in ec.java, then on ecframe on button action event call the mysql statement, and create the statement by calling the static connection con variable

package emailcollector;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.Statement;


public class ec {

    public static Connection con;
    public static void main(String[] args) {
        try{
            con = DriverManager.getConnection("jdbc:mysql://localhost", "admin", "pass");


        }catch(Exception e) {
    }
    }
}

ecframe.java

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
            String textFieldValue = jTextField1.getText();

        Statement stmt = (Statement) ec.con.createStatement();

            String email = textFieldValue;

            String insert = "INSERT INTO emails VALUES ('" + email + ")";

            stmt.executeUpdate(insert);
    } 

Answer 2

Instead of making things static, often times I like to make my components independent of one another. In particular, I like the way that JFileChooser and JColorChooser work, so I like to emulate their functionality here by using either a modal JDialog, or a JOptionPane.

For example, here's a simple panel that represents a form that takes an email:

class EmailForm extends JPanel {
    private JTextField emailField = new JTextField(20);

    public EmailForm() {
        add(new JLabel("Email"));
        add(emailField);
    }

    public String getEmail() {
        return emailField.getText();
    }
}

And in your main method, you'd simply say:

EmailForm form = new EmailForm();
int option = JOptionPane.showConfirmDialog(null, form, "Email", JOptionPane.YES_NO_OPTION);
if (option == JOptionPane.YES_OPTION) {
    System.out.println(form.getEmail());
}

Now, if in your case the form can't be made independent, and the class that holds that database connection represents a context without which the UI cannot function properly, then you might want to occasionally pass a dependency like that to the main form's constructor. Other than that, you can fiddle with actions, event listeners, or even the factory pattern as others have suggested.

Answer 3

There are a number of ways you could achieve this, this is just one (and it's a start of a very BASIC example of a possible Factory pattern)

You need to provide some way so that the ec class can expose its functionality...

Something more like...

public class EmailManager {

    private Connection con;

    protected Connection getConnection() {
        if (connection == null) {
            con = DriverManager.getConnection("jdbc:mysql://localhost", "admin", "pass");
        }
        return con;
    }

    public void close() throws SQLException {
        if (con != null) {
            con.close();
        }
        con = null;
    }

    public void insertEmail(String email) throws SQLException {
        Statement stmt = null;
        try {
            Statement stmt = getConnection().createStatement();
            int count = stmt.execute("insert into emails values ('" + email + "')");
            if (count != 1) {
                throw new SQLException("Failed to insert new email");
            }
        } finally {
            try {
                stmt.close();
            } catch (Exception exp) {
            }
        }
    }
}

Then in your UI class, you simple create an instance of ec and access it's methods as required...

private EmailManager manager;

/*...*/

protected EmailManager getEMailManager() {
    if (manager == null) {
        manager = new EmailManager();
    }
}

private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                         
    String textFieldValue = jTextField1.getText();
    try {
        getEMailManager().insertEmail(textFieldValue);
    } catch (SQLException exp) {
        JOptionPane.showMessageDialog(this, "Failed to insert email into database", "Error", JOptionPane.ERROR_MESSAGE);
        exp.printStackTrace();
    }
} 

No offense, but all of this is basic OO programming. You might like to take a read through Classes and Objects for more details and ideas

You may also like to take a look at Code Conventions for the Java Programming Language