如何获取参数化的类实例 [英] How to get parametrized Class instance

问题描述

由于引入了泛型，因此Class是参数化的，因此List.class会生成Class< List> ;.这是很清楚的。

我无法弄清楚如何获得参数化类型的Class实例，即Class< List< String >> 。像这样的代码片段：

  public class GenTest {
 static< T> T实例化（Class< T> clazz）抛出Exception {
 return clazz.newInstance（）; 
} 
 public static void main（String [] args）throws Exception {
 //有没有办法避免
下面的行不要使用@SuppressWarnings（ 未登记）？ 
 // ArrayList.class是Class< ArrayList>，但是我想
 //传入Class< ArrayList< String>> 
 ArrayList< String> l = GenTest.instantiate（ArrayList.class）; 
 
 
 $ / code $ / pre 
 
我经常碰到这个问题的变化，仍然不知道，如果我只是想念什么，或者如果真的没有更好的办法。感谢您的建议。
解决方案
 Class类是类型的运行时表示。由于参数化类型在运行时进行了类型擦除，所以Class的类对象将与Class< List< Integer>和Class< List< String>相同。 >您无法使用.class表示法实例化它们的原因是，这是用于类文字的特殊语法。  Java语言规范特别禁止此操作当参数类型为参数时，这就是为什么List< String> .class不被允许的原因。
 
Since generics were introduced, Class is parametrized, so that List.class produces Class<List>. This is clear.

What I am not able to figure out is how to get a instance of Class of type which is parametrized itself, i.e. Class<List<String>>. Like in this snippet:
public class GenTest {
    static <T> T instantiate(Class<T> clazz) throws Exception {
        return clazz.newInstance();
    }
    public static void main(String[] args) throws Exception {
        // Is there a way to avoid waring on the line below
        // without using  @SuppressWarnings("unchecked")?
        // ArrayList.class is Class<ArrayList>, but I would like to
        // pass in Class<ArrayList<String>>
        ArrayList<String> l = GenTest.instantiate(ArrayList.class);
    }
}
I run into variations of this problem quite often and I still don't know, if I just miss something, or if there is really no better way. Thanks for suggestions.
解决方案
The Class class is a run-time representation of a type. Since parametrized types undergo type erasure at runtime, the class object for Class would be the same as for Class<List<Integer>> and Class<List<String>>.

The reason you cannot instantiate them using the .class notation is that this is a special syntax used for class literals. The Java Language Specification specifically forbids this syntax when the type is parametrized, which is why List<String>.class is not allowed.

                        
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