[英]Instantiating an inner class
I have a utility method and when irrelevant logic is removed from it, the simplified method would look like this: 我有一个实用工具方法,当从中删除不相关的逻辑时,简化的方法将如下所示:
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;
}
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
. 问题是,如果
clazz
是一个内部类,如Foo.Bar.class
,那么即使Bar
是公共的, newInstance()
方法也不会工作,因为它会抛出一个java.lang.InstantiationException
。
Is there a way to dynamically instantiate inner classes? 有没有办法动态实例化内部类?
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. 如果它真的是一个内部类而不是嵌套 (静态)类,那么就有一个隐式构造函数参数,它是对外部类实例的引用。 You can't use
Class.newInstance
at that stage - you have to get the appropriate constructor. 你不能在那个阶段使用
Class.newInstance
- 你必须得到适当的构造函数。 Here's an example: 这是一个例子:
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() {}
}
}
Something more generic: 更通用的东西:
public static <T> T createInstance(final Class<T> clazz) throws SecurityException, NoSuchMethodException,
IllegalArgumentException, InstantiationException, IllegalAccessException, InvocationTargetException {
T instanceToReturn = null;
Class< ? > enclosingClass = clazz.getEnclosingClass();
if (enclosingClass != null) {
Object instanceOfEnclosingClass = createInstance(enclosingClass);
Constructor<T> ctor = clazz.getConstructor(enclosingClass);
if (ctor != null) {
instanceToReturn = ctor.newInstance(instanceOfEnclosingClass);
}
} else {
instanceToReturn = clazz.newInstance();
}
return instanceToReturn;
}
In Jmockit 1.41, use this: 在Jmockit 1.41中,使用:
ConstructorReflection.newInstance ConstructorReflection.newInstance
This exception will be thrown only if clazz represents either an abstract class or an interface. 仅当clazz表示抽象类或接口时,才会抛出此异常。 Are you sure you're passing a Class object that represents a concrete class?
您确定要传递代表具体类的Class对象吗?
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