Java反射从类名获取构造函数失败 [英] Java reflection get constructor from class name failed

问题描述

我有以下代码段：

class You{
    public You(String s){}
}

public static void main(String[] args)  throws NoSuchMethodException {
    Constructor[] constructors = You.class.getConstructors();
    for(Constructor constructor: constructors){
        Class[] parameterTypes = constructor.getParameterTypes();
        for(Class c: parameterTypes){
            System.out.println(c.getName());//print java.lang.String
        }
    }
    Constructor constructor =
            You.class.getConstructor(String.class);//NoSuchMethodException?
}

这很老了，当我打印构造函数时，它有一个 java.lang.String 作为参数。但是，当我尝试 You.class.getConstructor 时，它说没有以 String.class 作为参数的构造函数。

This is quite old, when I print the constructors, it has one constructor with java.lang.String as parameter. But when I tried to You.class.getConstructor it says no constructor with String.class as parameter.

我在Mac上使用 java1.8 。

非常感谢。

推荐答案

如果不是这种情况，我将删除此答案，但看起来您是一个内部类，并且我怀疑您的实际代码如下所示：

I'll delete this answer if it's not the case, but it looks like You is an inner class, and I suspect your actual code looks something like this:

public class Foo {

    class You {
        public You(String s){}
    }

    public static void main(String[] args)  throws NoSuchMethodException {
        Constructor[] constructors = You.class.getConstructors();

        for (Constructor constructor: constructors) {
            Class[] parameterTypes = constructor.getParameterTypes();

            for (Class c: parameterTypes){
                System.out.println(c.getName());//print java.lang.String
            }
        }

        Constructor constructor =
            You.class.getConstructor(String.class);//NoSuchMethodException?
    }
}

来自文档 $ c> Class＃getConstructor ：

From the documentation of Class#getConstructor:

如果此Class对象表示在非静态中声明的内部类在上下文中，形式参数类型包括显式的封闭实例作为第一个参数。

If this Class object represents an inner class declared in a non-static context, the formal parameter types include the explicit enclosing instance as the first parameter.

因此，您必须使用

Constructor constructor = You.class.getConstructor(Foo.class, String.class);

但显然将 Foo 替换为您的封闭课程。

But obviously replace Foo with the name of your enclosing class.

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