************************用反思回答**************************
首先,您将这样声明您的新注释:
@Target(ElementType.METHOD)
@Retention(RetentionPolicy.RUNTIME)
public @interface CarListener{
public String carAction();
}
因此,在您的班级 Car 中,您将拥有:
public class Car {
//Here you´ll be looking at all the methods you have in the class Car (I´d advice to
// put them in another class, so as to keep it clean, I didn´t do it here in order to
// explain it better. These methods have the corresponding annotation you created
public void listener(String e) {
Method[] methods = Car.class.getMethods();
for(Method method:methods) {
//Now that you have all the methods all you need is to figure which one you want
// you´ll do that according to the "e" string, which represents the car action (for
// example "Honk") I´d also advice you to rename that too.
if(rightMethod(method, e))
//Now that you have found it, then you invoke the method, "call it"
// which is what you wre doing in the previos code with "this.blowHorn()"
return invokeMethod(method);
}
//This will help you in case you did NOT find the correct method, it´s just help
// if you don´t put it in it won´t break your code
// fun fact about RuntimExceptions: you don´t have to declare them, meaning
// you dont have to add them as "throws" or catch
throw new RuntimeException("No listener found for car Action"+e);
}
private boolean rightMethod(Method method, String expression) {
//First if asks if the method found has an annoation present, and if it does
// then it asks if it corresponds to the annoation you created
if (method.isAnnotationPresent(NewAnnotationInterfaceName.class))
//if the method in fact has the annotation created all you are doing is asking what
// carAction is associated to that method, you do that with the .carAction()
return method.getAnnotation(NewAnnotationInterfaceName.class).carAction().equals(expression);
return false;
}
//Now all you have to do is invoke it :) This just follows how to invoke a method
// I won´t explain it
private void invokeMethod(Method method) {
try {
return method.invoke(Car.class.newInstance(), new Object[]{});
} catch (InstantiationException | IllegalAccessException
| InvocationTargetException | IllegalArgumentException ex) {
Logger.getLogger(Car.class.getName()).log(Level.SEVERE, null, ex);
}
throw new RuntimeException("Could not invoke method");
}
@CarListener(carAction= "Honk")
public void blowHorn() {
...
}
@CarListener(carAction= "SomethingElse")
public void someOtherAction() {
...
}
}
希望有帮助!
*******************用Hashmap和命令设计回答****************************
public abstract class CarAction {
public abstract void execute(Car car){};
}
public class HonkAction extends CarAction{
@Override
public void execute(Car car) {
car.blowHorn();
}
}
public class Car {
private HashMap<String, CarAction> carActions;
public Car() {
...
initializeCarActions();
}
public void initializeCarActions() {
this.carActions = new HashMap<>();
this.carActions.put("Honk", new HonkAction());
...
}
public void listener(String e) {
CarAction action = this.carActions.get(e);
if(action!=null) action.execute(this);
}
}
如果您要使用这种方式,我建议有人注入 HashMap,这样 Car 就不必依赖 CarActions(只是抽象类),要么使用一个类,要么使用 Guice。此外,如果所有 carAction 只需要“Car”即可执行,这也有效。
祝你好运!