Referring to a variable from outside static Connection method

Question

I am new to java and started doing a javaFX project. In this project, I receive a variable from a previous frame, and use it to execute an SQL query in order to render the table based on that particular variable. Here is my code:

package financials;

import java.net.URL;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.Statement;
import java.util.ResourceBundle;

import javafx.collections.FXCollections;
import javafx.collections.ObservableList;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;

import javax.swing.JOptionPane;

/**
 * FXML Controller class
 *
 * @author param
 */
public class theControl implements Initializable {
    @FXML
    private Label test;

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        Statement st;
        Connection con = null;    
    }

    /**
     *
     * @param name
     */
    public void previous(String name) {
        System.out.println(name);
    }
       
    public static Connection ConnectDB() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost/database", "root", "Password");
            
            return con;
        } catch(Exception ae) {
            JOptionPane.showMessageDialog(null, ae);

            return null;
        }
    }

    public static ObservableList<RenderNow> getListAccount() {
        Connection con = ConnectDB();
        ObservableList<RenderNow> list = FXCollections.observableArrayList();
        try {
            PreparedStatement pst = con.prepareStatement("SELECT * FROM lines WHERE Code=? ");
            pst.setString(1, name); //This is where I am having trouble
            ResultSet rs = pst.executeQuery();
            while (rs.next()) {
                list.add(new SBRender(rs.getString("Account1"), rs.getString("Account2"), rs.getString("Account3"), rs.getString("Account4"), rs.getString("Account5")));
            }         
        } catch(Exception ae) {
            JOptionPane.showMessageDialog(null, ae);

            return null;                          
        }

        return list;  
    }
}

The problem is that the variable name is not being recognized in the pst.setString line. The error I am getting is that variable 'name' is not found. I tried a different approach where I used name to set the text of Label test, and then later tried to get the variable in the public static Connection ConnectDB() method.

Something like:

public class theControl implements Initializable {
    @FXML
    private Label test;

    /**
     * Initializes the controller class.
     */
    @Override
    public void initialize(URL url, ResourceBundle rb) {
        Statement st;
        Connection con = null;
    }

    /**
     *
     * @param name
     */
    public void previous(String name) {
        System.out.println(name);
        test.setText(name); //Where i set the text of label 'text'
    }
   
    public static Connection ConnectDB() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            Connection con = DriverManager.getConnection("jdbc:mysql://localhost/database", "root", "Password");
            
            return con;
        } catch(Exception ae) {
            JOptionPane.showMessageDialog(null, ae);

            return null;
        }
    }

    public static ObservableList<RenderNow> getListAccount() {
        String name2 = test.getText(); //Where I try and get the text from label 'text'
        Connection con = ConnectDB();
        ObservableList<RenderNow> list = FXCollections.observableArrayList();
        try {
            PreparedStatement pst = con.prepareStatement("SELECT * FROM lines WHERE Code=? ");
            pst.setString(1, name2); //This is where I am having trouble
            ResultSet rs = pst.executeQuery();
            while (rs.next()) {
                list.add(new SBRender(rs.getString("Account1"), rs.getString("Account2"), rs.getString("Account3"), rs.getString("Account4"), rs.getString("Account5")));
            }
        } catch(Exception ae) {
            JOptionPane.showMessageDialog(null, ae);

            return null;                           
        }

        return list;  
    }
}

However, this attempt returns an error non-static variable test cannot be referenced from a static context. My understanding is that since the label test is not static, static Connection is unable to get the text. Is there any work around for this ?

Answer 1

In your first case, the variable was not set. It's only available on the method where you have your print method.

In the second case, you are not using the object. The test variable is in one object, so not accessible by static method which are not depending of object.

I suggest you to ad new parameter to your static method, and use like this:

// create new static method which require the name in parameters
public static ObservableList<RenderNow> getListAccountWithName(String name) {
    Connection con = ConnectDB(); // get DB thanks to static method
    ObservableList<RenderNow> list = FXCollections.observableArrayList();
    try {
        PreparedStatement pst = con.prepareStatement("SELECT * FROM lines WHERE Code = '?'");
        pst.setString(1, name); // now you can use name value
        ResultSet rs = pst.executeQuery();
        while (rs.next()) {
            list.add(new SBRender(rs.getString("Account1"), rs.getString("Account2"), rs.getString("Account3"), rs.getString("Account4"), rs.getString("Account5")));
        }
    } catch(Exception ae) {
        JOptionPane.showMessageDialog(null, ae);
        return null;                           
    }

    return list;  
}

And now, you can call it from the object like:

ObservableList<RenderNow> accounts = getListAccountWithName(test.getText());
// now what you have what you are looking for