[英]How do I reflect a private static nested subclass?
首先,我正在 Kotlin 中寻找答案,但我正在与 Java 库进行交互。
我需要从一个私有静态嵌套类中获取一个实例,该类派生自周围超类的一个实例。
鉴于您有这些(简化的)嵌套 Java 类
public abstract class GLFWKeyCallback extends Callback implements GLFWKeyCallbackI {
public static GLFWKeyCallback create(GLFWKeyCallbackI instance) {
new Container(instance.address(), instance);
}
private static final class Container extends GLFWKeyCallback {
private final GLFWKeyCallbackI delegate;
Container(long functionPointer, GLFWKeyCallbackI delegate) {
super(functionPointer);
this.delegate = delegate;
}
}
}
我通过另一种外部方法将 Container 实例作为 GLFWKeyCallback 取回。 您可以将此方法视为:
public static GLFWKeyCallback getCallback() {
return GLFWKeyCallback.create(anInternalInstance)
}
在科特林:
val callback:GLFWKeyCallback = getCallback()
// I would now want to cast,
// or in other ways use callback
// as the GLFWKeyCallback.Container class it actually is.
val callbackAsContainer = callback as GLFWKeyCallback.Container // Error: Container is private
val ContainerClass = GLFWKeyCallback::class.nestedClasses.find { it.simpleName?.contains("Container") ?: false }!!
// Gives me a KClass<*> that I don't know how to use, can't find documentation for this kind of circumstance
// If using the class instance itself is not possible I would at least want to get the
// Container.delegate of GLFWKeyCallbackI
val delegateField = ContainerClass.memberProperties.findLast { it.name == "delegate" }!!
val fieldValue = field.get(callback)
// Error: Out-projected type 'KProperty1<out Any, Any?>' prohibits the use of 'public abstract fun get(receiver: T): R defined in kotlin.reflect.KProperty1'
为什么你不想使用 Java 反射? 您也可以在 Kotlin 中使用它:
val callback = getCallback()
val field = callback::class.java.getDeclaredField("delegate")
field.isAccessible = true
val delegate = field.get(callback) as GLFWKeyCallbackI
您仍然可以通过.getClass()
获取课程。 此示例打印“5”:
public class Example {
public static void main(String[] args) throws Exception {
Object o = Target.get();
Field f = o.getClass().getDeclaredField("field");
f.setAccessible(true);
Integer i = (Integer) f.get(o);
System.out.println(i);
}
}
public class Target {
public static Object get() { return new Inner(); }
private static class Inner {
private int field = 5;
}
}
如果您知道确切的名称:
Class<?> c = Class.forName("com.foo.pkgof.Target$Inner");
c.getDeclaredField("field");
作品。 注意美元。 这是在“外部”和“内部”之间使用的分隔符。
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