從另一個類獲取變量值

Question

因此，我有一個名為Members的類，還有另一個名為DBConnect類，該類將連接到數據庫，然后將數據庫中的值存儲到Members類。 然后，我想在另一個名為Controller類中使用來自Members類的值。 但是，我在Controller類中創建了Object的新實例，如果從那里使用get()方法，它將導致返回null 。

但是，如果我在DBConnect類中執行所有操作，則可以。 它將返回名字而不是null

Members等級

package Database;

public class Members {

    private String firstName;

    public String getFirstName() {
        return firstName;
    }

    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

DBConnect類

package Database;

import java.sql.*;

public class DBConnect {
    private Connection connection;
    private Statement statement;
    private ResultSet resultSet;

    Members members = new Members();

    public DBConnect() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");

            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/finance", "root", "");
            statement = connection.createStatement();
            System.out.println("Successfully connected to DATABASE.");
        } catch (Exception ex) {
            System.out.println("ERROR: Can't connect to the Database! -> " + ex);
        }
    }

    public void getData(int id) {
        try {
            String query = "select * from Members where MembersId = '" + id + "'";
            resultSet = statement.executeQuery(query);

            while (resultSet.next()) {
                members.setId(resultSet.getInt("MembersId"));
                members.setFirstName(resultSet.getString("MembersFirstName"));
                members.setLastName(resultSet.getString("MembersLastName"));
                members.setPosition(resultSet.getString("MembersPosition"));
                members.setHourlyRate(resultSet.getDouble("MembersHourlyRate"));
                members.setGraduated(resultSet.getString("MembersGraduated"));
                members.setLanguages(resultSet.getString("MembersLanguages"));
                members.setCountry(resultSet.getString("MembersCountry"));
                members.setCity(resultSet.getString("MembersCity"));
                members.setAddress(resultSet.getString("MembersAddress"));
            }
        }catch (Exception ex) {
            System.out.println("Error: " + ex);
        }
    }
}

Controller類

package sample;

import Database.DBConnect;
import Database.Members;
import javafx.fxml.FXML;
import javafx.fxml.Initializable;
import javafx.scene.control.Label;
import javafx.scene.effect.DropShadow;
import javafx.scene.image.Image;
import javafx.scene.input.MouseEvent;
import javafx.scene.layout.HBox;
import javafx.scene.paint.Color;
import javafx.scene.paint.ImagePattern;
import javafx.scene.shape.Circle;

import java.io.IOException;
import java.net.URISyntaxException;
import java.net.URL;
import java.util.ResourceBundle;


public class Controller implements Initializable {

    private DBConnect dbConnect;
    private Members members;

@FXML
    private HBox sidebarMembers;

@FXML
    private void openSidebarMembers(MouseEvent event) throws IOException {
        dbConnect = new DBConnect();
        dbConnect.getData(2);
        members = new Members();
        if (event.getSource() == sidebarMembers) {
            System.out.println(members.getFirstName());
        }
    }

據我了解，當您創建一個新對象時，它將導致將所有變量初始化為0。除了使它們成為靜態對象之外，我還應該如何訪問這些值？

所以我的問題是，我怎么能訪問我設置為我的價值觀Members類從DBConnect類在我的Controller類？

Answer 1

在DbConnect類中，將getData方法的返回類型更改為Member。

public Member getData(int id)

現在，您可以從控制器訪問該成員

Member member = dbConnect.getData(2);