Java實現類似函數指針功能

Java中大家對addListener之類的方法必須實現一個Listener接口的類（匿名類或內部類），感覺很麻煩，甚至吵著要Java改語法，實現一級函數，Java 8 的lambda表達式終於解決了這個問題，但是其實不用動語法，我們還有別的辦法。最簡單的想法，如果Java有函數指針，這個問題就好解決了，不過，雖然Java沒有函數指針，卻能反射，我們一樣可以實現類似函數指針的功能。

ActionHelper用於javafx，其他場景類推

import java.lang.reflect.InvocationTargetException;
import java.lang.reflect.Method;

import javafx.event.ActionEvent;
import javafx.event.EventHandler;

public class ActionHelper {

public static EventHandler<ActionEvent> handle(Object obj,String methodName,Object... param){
return new Action(obj,methodName,param);
}


private static class Action implements EventHandler<ActionEvent>{
private Object obj;
private String methodName;
private Class<?>[] clazz;
private Object[] param;
public Action(Object obj,String methodName,Object... param){
this.obj = obj;
if(param.length>0){
clazz = new Class[1+param.length];
clazz[0] = ActionEvent.class;
for(int i=0;i<param.length;i++){
clazz[1+i] = param[i].getClass();
}
this.param = new Object[1+param.length];
for(int i=0;i<param.length;i++){
this.param[1+i] = param[i];
}
}else{
clazz = new Class[1];
clazz[0] = ActionEvent.class;
this.param = new Object[1];
}
this.methodName = methodName;
}

@Override
public void handle(ActionEvent event) {
try {
Method method = obj.getClass().getDeclaredMethod(methodName, clazz);
if(method != null){
method.setAccessible(true);
param[0] = event;
method.invoke(obj, param);
}
} catch (NoSuchMethodException e) {
e.printStackTrace();
} catch (SecurityException e) {
e.printStackTrace();
} catch (IllegalAccessException e) {
e.printStackTrace();
} catch (IllegalArgumentException e) {
e.printStackTrace();
} catch (InvocationTargetException e) {
e.printStackTrace();
}
}

}
}

//以下為使用的代碼片段，javafx的右鍵菜單
ContextMenu ctxMenu = new ContextMenu();
MenuItem mitem = new MenuItem("查看頁面");
mitem.setOnAction(ActionHelper.handle(this, "viewPage"));
ctxMenu.getItems().add(mitem);

private void viewPage(ActionEvent event){
//do some thing
}