从另一个类获取变量值

Question

所以我有一个名为Members 的类，我还有另一个名为DBConnect 的类，它将连接到数据库，然后将数据库中的值存储到Members 类。然后我想在另一个名为Controller 的类中使用Members 类中的值。但是，我在 Controller 类中创建了 Object 的一个新实例，如果我从那里使用方法 get()，它将导致返回 null。

但是，如果我在 DBConnect 类中执行所有操作，那就没问题了。它将返回名字而不是 null

Members类

package Database;

public class Members {

    private String firstName;

    public String getFirstName() {
        return firstName;
    }

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

DBConnect类

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类

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());
        }
    }

我的理解是，当您创建一个新对象时，它会导致将所有变量初始化回 0。除了将它们设为静态之外，我还应该如何访问这些值？

所以我的问题是，如何从 DBConnect 类中的 DBConnect 类访问我为 Members 类设置的值？

Answer 1

在 DbConnect 类中将 getData 方法的返回类型更改为 Member。

public Member getData(int id)

现在您可以从控制器访问该成员

Member member = dbConnect.getData(2);