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I have three class as following:
public class TestEntity { } public class BaseClass<TEntity> { } public class DerivedClass : BaseClass<TestEntity> { } I already get the System.Type object of DerivedClass using reflection in runtime. How can I get the System.Type object of TestEntity using reflection?
Thanks.
766
You can get around the superfluous reference by providing a generic static factory method. Something like public static <T> GenericClass<T> of(Class<T> type) {...} and then call it as such: GenericClass<String> var = GenericClass. of(String. class) .
A generic type is declared by specifying a type parameter in an angle brackets after a type name, e.g. TypeName<T> where T is a type parameter.
The short answer is, that there is no way to find out the runtime type of generic type parameters in Java. A solution to this is to pass the Class of the type parameter into the constructor of the generic type, e.g.
Generic Methods A type parameter, also known as a type variable, is an identifier that specifies a generic type name. The type parameters can be used to declare the return type and act as placeholders for the types of the arguments passed to the generic method, which are known as actual type arguments.
I assume that your code is just a sample and you don't explicitly know DerivedClass.
var type = GetSomeType(); var innerType = type.BaseType.GetGenericArguments()[0]; Note that this code can fail very easily at run time you should verify if type you handle is what you expect it to be:
if(type.BaseType.IsGenericType && type.BaseType.GetGenericTypeDefinition() == typeof(BaseClass<>)) Also there can be deeper inheritance tree so some loop with above condition would be required.
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You can use the BaseType property. The following code would be resilient for changes in the inheritance (e.g. if you add another class in the middle):
Type GetBaseType(Type type) { while (type.BaseType != null) { type = type.BaseType; if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(BaseClass<>)) { return type.GetGenericArguments()[0]; } } throw new InvalidOperationException("Base type was not found"); } // to use: GetBaseType(typeof(DerivedClass)) If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
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