为什么在CustomerService Service = serviceFactory.getInstance（）。getServiceType（serviceType.customer）;

Question

superservice：

package service;

public interface SuperService {
}

customerService：

package service.custom;

import dto.Customer;

import java.util.List;

public interface CustomerService{
    boolean add(Customer customer);
    Customer search(String id);
    boolean update(String id, Customer customer);
    boolean delete(String id);
    List<Customer> getAll();
}

customerServiceImpl：

package service.custom.impl;

import dto.Customer;


public class CustomerServiceImpl{
    public boolean add(Customer customer) {
        return false;
    }
}

serviceFactory：

package service;

import service.custom.impl.CustomerServiceImpl;
import service.custom.impl.ItemServiceImpl;
import service.custom.impl.OrderServiceImpl;
import util.ServiceType;

public class ServiceFactory {
    private static ServiceFactory instance;

    private ServiceFactory(){

    }

    public static ServiceFactory getInstance(){
        if(instance==null){
            instance= new ServiceFactory();
        }
        return instance;
    }

    public <T extends SuperService> T getServiceType(ServiceType type){
        switch (type){
            case CUSTOMER:return (T) new CustomerServiceImpl();
            case ITEM:return (T) new ItemServiceImpl();
            case ORDER:return (T) new OrderServiceImpl();
        }
        return null;
    }
}

customerFormController：

package controller;

import com.jfoenix.controls.JFXButton;
import com.jfoenix.controls.JFXTextField;
import dto.Customer;
import javafx.event.ActionEvent;
import javafx.fxml.FXML;
import javafx.scene.control.TableColumn;
import javafx.scene.control.TableView;
import service.ServiceFactory;
import service.custom.CustomerService;
import util.ServiceType;

public class CustomerFormController {

    @FXML
    private JFXButton btnAdd;

    @FXML
    private JFXButton btnDelete;

    @FXML
    private JFXButton btnReload;

    @FXML
    private JFXButton btnSearch;

    @FXML
    private JFXButton btnUpdate;

    @FXML
    private TableColumn<?, ?> colAddress;

    @FXML
    private TableColumn<?, ?> colId;

    @FXML
    private TableColumn<?, ?> colName;

    @FXML
    private TableColumn<?, ?> colSalary;

    @FXML
    private TableView<?> tblCustomers;

    @FXML
    private JFXTextField txtAddress;

    @FXML
    private JFXTextField txtId;

    @FXML
    private JFXTextField txtName;

    @FXML
    private JFXTextField txtSalary;



    @FXML
    void btnAddOnAction(ActionEvent event) {
        String idText = txtId.getText();
        String nameText = txtName.getText();
        String addressText = txtAddress.getText();
        double salary = Double.parseDouble(txtSalary.getText());

        Customer customer = new Customer(idText, nameText, addressText, salary);
        CustomerService service = ServiceFactory.getInstance().getServiceType(ServiceType.CUSTOMER);
        service.add(customer);
    }

    @FXML
    void btnDeleteOnAction(ActionEvent event) {

    }

    @FXML
    void btnReloadOnAction(ActionEvent event) {

    }

    @FXML
    void btnSearchOnAction(ActionEvent event) {

    }

    @FXML
    void btnUpdateOnAction(ActionEvent event) {

    }
}

这是一种分层的架构设计，在这里，我试图使用工厂设计模式将

CustomerServiceImpl

对象从服务层传递到控制器/演示层。我试图了解有限的类型通用物，并决定进行实验以了解概念，然后才遇到问题。您能帮我理解为什么

CustomerService service = ServiceFactory.getInstance().getServiceType(ServiceType.CUSTOMER);

没有编译错误，因为

CustomerService

没有扩展

SuperService

CustomerServiceImpl

CustomerService

没有实现

CustomerService

引用不能用于

CustomerServiceImpl

对象？

Answer 1

public <T extends SuperService> T getServiceType(ServiceType type){
    switch (type){
        case CUSTOMER:return (T) new CustomerServiceImpl();
        case ITEM:return (T) new ItemServiceImpl();
        case ORDER:return (T) new OrderServiceImpl();
    }
    return null;
}

在适当的位置上，您基本上将所有sumpers施放到超级服务中。

现在，由于SuperService是一个接口，您不会收到编译错误，但是您会遇到运行时错误！

基本上归结为：

casting到无关接口不会给您编译错误。

更多信息可以在此处找到：cast铸造到无关接口时，它为什么会编译？