How can I get a Java `Class` from a `KClass`? For ...

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[poohbar]

How can I get a Java Class from a KClass? For example I have

KClassImpl "class kotlin.String"

and I want to get Java’s String.class from it

I tried:

JvmClassMappingKt.getJavaClass(klass)

but it returns class kotlin.reflect.jvm.internal.KClassImpl 😕

[streetsofboston]

MyClass::class.java

[poohbar]

I need it at runtime. Not compile time.

[jw]

.java is a property that works at runtime

[poohbar]

Oh, I think .java is a Kotlin extension property but I have to do this call from Java.

[Casey Brooks]

You should be able to access that same property from Java code with JvmClassMappingKt.getJavaClass(aClass);

[poohbar]

Ok, let me give a full example. I have a simple Kotlin data class and an instance of it in variable type. I am trying to get the Java class of the first parameter of the data class’s constructor:

KClass<?> klass = JvmClassMappingKt.getKotlinClass(type);
KFunction<?> primaryConstructor = KClasses.getPrimaryConstructor(klass);
List<KParameter> parameters = primaryConstructor.getParameters();
KParameter firstParameter = parameters.get(0);
KType parameterType = firstParameter.getType();
JvmClassMappingKt.getJavaClass(parameterType.getClassifier())

[poohbar]

This snippet returns kotlin.reflect.jvm.internal.KClassImpl as the result and I would expect java.lang.String.

[poohbar]

The weird thing is that if I look at the result of getClassifer() in debugger I do see the jClass there:

[poohbar]

Figured it out. It was calling the wrong overload of getJavaClass. Changing the last line to:

JvmClassMappingKt.getJavaClass((KClass) parameterType.getClassifier());

fixed it.