java Java泛型和反射！
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/939903/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
Java Generics and reflection!
提问by Jay
I have a class that looks like this:
我有一个看起来像这样的课程：
public class UploadBean {
protected UploadBean(Map<String,?> map){
//do nothing.
}
}
To use reflection and create a object by invoking the corresponding constructor, I wrote code as follows:
为了使用反射，通过调用对应的构造函数来创建对象，我写了如下代码：
Class<?> parTypes[] = new Class<?>[1];
parTypes[0] = Map.class;
Constructor ct = format.getMappingBean().getConstructor(parTypes);
Object[] argList = new Object[1];
argList[0] = map;
Object retObj = ct.newInstance(argList);
This code fails at runtime with "No Such Method Exception". Now, how do I set the param type correctly?! such that the generic map argument in the constructor is identified?
此代码在运行时失败，并显示“无此类方法异常”。现在，如何正确设置参数类型？！以便识别构造函数中的通用映射参数？
回答by Jon Skeet
The constructor is protected - if you make it public oruse getDeclaredConstructorinstead of getConstructorit should work.
构造函数是受保护的 - 如果您将其公开或使用它getDeclaredConstructor来代替getConstructor它应该可以工作。
(You'll need to use setAccessibleif you're trying to call this from somewhere you wouldn't normally have access.)
（setAccessible如果您尝试从通常无法访问的地方调用它，则需要使用。）
EDIT: Here's a test to show it working okay:
编辑：这是一个测试，表明它可以正常工作：
import java.lang.reflect.*;
import java.util.*;
public class UploadBean {
// "throws Exception" just for simplicity. Not nice normally!
public static void main(String[] args) throws Exception {
Class<?> parTypes[] = new Class<?>[1];
parTypes[0] = Map.class;
Constructor ct = UploadBean.class.getDeclaredConstructor(parTypes);
Object[] argList = new Object[1];
argList[0] = null;
Object retObj = ct.newInstance(argList);
}
protected UploadBean(Map<String,?> map){
//do nothing.
}
}
回答by fortran
The generic information is not available at runtime, it's just for static analysis, so do it as if the generics didn't exist.
泛型信息在运行时不可用，它只是用于静态分析，所以就好像泛型不存在一样。
回答by Rob Di Marco
I believe you need to call
我相信你需要打电话
ct.setAccessible(true)
The setAccessible method allows you to override access methods.
setAccessible 方法允许您覆盖访问方法。
