Java:通过关联覆盖行为

Question

我有几个Field实体，Controller以这种方式与它们相关联：(Field,Generic_Controller <--> Specific_Controller) .我想在 Java 中实现每个Specific_Controller与相应Field和Generic_Controller的关联。我怎样才能做到这一点？编译时更好。

编辑：这是一个任务的伪代码（也许会更清楚）：

given X:Class and C:ServiceFor[X]
  where C:ServiceFor[X] means:
    C has method M with args(x:X) returning Any
goal:
get C:ServiceFor[X]
  where C and X are given. // X is Field class or instance
that:
  if there exits explicitly defined (C1 as ServiceFor[X]) and (C1 is child of C)
    return C1 // ==Specific_Controller
  otherwise:
    return C  // ==Generic_Controller

目前，我有实现，但它不是 DRY：我应该将控制器类与getController主体保持同步。_{这是可能的方法之一，可能会导致问题（如果好奇，请参阅问题的第一个版本）。}

import javax.swing.*;
interface Field 
{
  Object getValue();
  /** Obtain name of field for internal usage
   */
  String getName(); 
  void setValue<T>(T value) throws InvalidValueException;
  boolean isValid<T>(T value);
  Controller getController(Class<?> genericController);
}
interface Controller {}
interface UIController extends Controller {
  /** Return GUI widget responsible to manipulating value inside FormField 
   *  instance
   * (Control logic uses setValue() ) */
  JComponent getInputControl();
}
interface UrlEncoder extends Controller {
  /** Obtain value encoded for transmition through Web.
   *
   * some fields used privately in code are cut out inside this method
   */
  String getURLEncodedValue(); 
}
class CommonUIController implements UIController { ... }
//-- MyField with specific implementations of controllers
class MyField 
    implements Field, UIController, UrlEncoder 
{
  // here methods overriden
}
//-- usage (i do it every time)
MyField mf;
UIController uiController;
if(mf instanceof UIController)
  uiController = (UIController)mf;
} else { // use default impl.
  uiController = new CommonUIController(mf);
}

我希望保持Field，Controller和宣布的关系彼此分开。就像这样C++可以做到：

//-- common.hpp
template<class _Controller, class _Field>
struct overriden_controller:
    public _Controller
{
  typedef _Controller controller_type;
  typedef _Controller type;
  typedef _Field      field_type;
};
struct UrlEncoder{};
struct UIController {};

//-- MyField.hpp
// Field knows nothing about controllers
struct MyField {};
// !! Here comes association
template<>
struct overriden_controller<UIController, MyField>
{
   // Overriden behavior 
};
template<>
struct overriden_controller<UrlEncoder, MyField>
{
   // Overriden behavior 
};
//-- And then use associated value
auto controller = new field_controller<UIController, MyField>::type();

您能在这里提出什么建议？

Answer 1

在我看来，

通过将接口作为参数传递来获取类的实例似乎有点做作，除非您使用一些咬码编织来填充该方法，但是......

使用一些约定而不是配置，您可以实现如下内容：

public class AbstractField {
    public Controller getController(Class clazz){
        String name = clazz.getSimpleName();
        String pack = clazz.getPackage().getName();
        String controllerName = pack+"."+getClass().getSimpleName()+name;
        Class<?> ctrl = null;
        try {
            ctrl = Class.forName(controllerName);
            return (Controller) ctrl.newInstance();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (InstantiationException e) {
            e.printStackTrace();
        } catch (IllegalAccessException e) {
            e.printStackTrace();
        }
        return null;
    }
}