方法在java中返回动态类型 [英] method returning dynamic type in java

问题描述

如何写一个方法（如果有的话）会返回一个动态类型

类似于

  public X createRequestObject（Class xclass，String url，String username，String password）{
 X x = Class.forName（xclass.getCannonicalName（））。getConstructor String.class）.newInstance（URL）; 
 x.setheader（AUTHORIZATION，createHeader（username，password）
 return x 
} 
  

，然后我可以像使用它一样使用它。

  HttpGet httpGet = createRequestObject（HttpGet.class，http ：//wwwww.google.com，username，password）; 
 
或
 
 HttpPost httpPost = createRequestObject（HttpPost.class，http：// wwww .google.com，username，password）; 
  

我知道我可以返回一个对象然后抛出它，但我不喜欢演员，所以想知道是否有一个构造在Java中，可以帮助我做到这一点

简单，将该方法声明为泛型，声明它的返回类型及其类：

  public< T> T foo（Class< T> clazz，Object ... args）{
 return null; 
} 
  

<显然这些参数是不同的，你可以用下面的方法实例化一个新的 T ：

  clazz.newInstance（）; 
  

为无效构造函数。

一个带参数的构造函数（在本例中是String s和Object o）：

  return x.getConstructor（String.class，Object。 class）.newInstance（s，new Object（））; 
  

事实上，感谢您的可变参数，您可以遍历数组并获取所有必需的类对象

然后你就可以安全地做：

 字符串s = foo（String.class，a，b）; 
  

如果您想将T限制为 HttpRequest use：



  public< T extends HttpRequest> T foo（Class< T> clazz，Object ... args）
  




How can I write a method (if at all i can) that would return a dynamic type

something like

public X createRequestObject(Class xclass , String url , String username , String password){
   X x = Class.forName(xclass.getCannonicalName()).getConstructor(String.class).newInstance(url);
   x.setheader("AUTHORIZATION" , createHeader(username,password)
   return x
}

and then i can use it like

HttpGet httpGet = createRequestObject(HttpGet.class , "http://wwww.google.com , "username","password");

or 

HttpPost httpPost = createRequestObject(HttpPost.class , "http://wwww.google.com , "username","password");

I know i can return an object and then cast it later but i dislike casts so wondering if there is a construct in java that can help me do this

解决方案

Simply, declare the method as generic, declare its return type, and its class:

public <T> T foo(Class<T> clazz, Object... args) {
    return null;
} 

Obviously the parameters are different that what one would need. You can instantiate a new T with:

clazz.newInstance();

for a nullary constructor.

For a constructor with arguments(in this example String s and Object o):

return x.getConstructor(String.class, Object.class).newInstance("s", new Object());

In fact, thanks to your varargs you can iterate through the array and get all necessary class objects for the constructor lookup.

You can then safely do:

String s = foo(String.class, "a", "b");

If you want to constrain T to be a subclass of HttpRequest use:

public <T extends HttpRequest> T foo(Class<T> clazz, Object... args)

这篇关于方法在java中返回动态类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！