实例化内部类 [英] Instantiating an inner class

问题描述

我有一个实用工具方法，当从中删除不相关的逻辑时，简化的方法如下所示：

I have a utility method and when irrelevant logic is removed from it, the simplified method would look like this:

public static <A extends Foo> List<A> getFooList(Class<A> clazz) {
   List<A> returnValue = new ArrayList<A>();
   for(int i=0; i < 5; i++) {
        A object = clazz.newInstance();
        returnValue.add(object);
   }

   return returnValue;
}

问题是，如果 clazz 是一个内部类，如 Foo.Bar.class ，那么 newInstance（）方法不会即使 Bar 是公开的，因为它会抛出 java.lang.InstantiationException 。

The problem is, that if clazz is an inner class such as Foo.Bar.class, then the newInstance() method will not work even if Bar would be public, as it will throw a java.lang.InstantiationException.

有没有办法动态实例化内部类？

Is there a way to dynamically instantiate inner classes?

推荐答案

如果真的是 inner 类而不是嵌套（静态）类，有一个隐式构造函数参数，它是对外部类实例的引用。你不能在那个阶段使用 Class.newInstance - 你必须得到适当的构造函数。这是一个例子：

If it's genuinely an inner class instead of a nested (static) class, there's an implicit constructor parameter, which is the reference to the instance of the outer class. You can't use Class.newInstance at that stage - you have to get the appropriate constructor. Here's an example:

import java.lang.reflect.*;

class Test
{
    public static void main(String[] args) throws Exception
    {
        Class<Outer.Inner> clazz = Outer.Inner.class;

        Constructor<Outer.Inner> ctor = clazz.getConstructor(Outer.class);

        Outer outer = new Outer();
        Outer.Inner instance = ctor.newInstance(outer);
    }
}

class Outer
{
    class Inner
    {
        // getConstructor only returns a public constructor. If you need
        // non-public ones, use getDeclaredConstructors
        public Inner() {}
    }
}

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