CODEWITHSUNDEEP
javareflection
bwawok
bwawok

Reputation: 15347

How to get concrete type of a generic interface

I have an interface

public interface FooBar<T> { }

I have a class that implements it

public class BarFoo implements FooBar<Person> { }

With reflection, I want to take an instance of BarFoo and get that the version of FooBar it implements is Person.

I use .getInterfaces from BarFoo to get back to FooBar, but that doesn't help me find out what T is.

Upvotes: 24

Views: 30828

Answers (2)

BalusC
BalusC

Reputation: 1108692

You can grab generic interfaces of a class by Class#getGenericInterfaces() which you then in turn check if it's a ParameterizedType and then grab the actual type arguments accordingly.

Type[] genericInterfaces = BarFoo.class.getGenericInterfaces();
for (Type genericInterface : genericInterfaces) {
    if (genericInterface instanceof ParameterizedType) {
        Type[] genericTypes = ((ParameterizedType) genericInterface).getActualTypeArguments();
        for (Type genericType : genericTypes) {
            System.out.println("Generic type: " + genericType);
        }
    }
}

Upvotes: 50

matt b
matt b

Reputation: 139921

Try something like the following:

Class<T> thisClass = null;
Type type = getClass().getGenericSuperclass();
if (type instanceof ParameterizedType) {
    ParameterizedType parameterizedType = (ParameterizedType) type;
    Type[] typeArguments = parameterizedType.getActualTypeArguments();
    thisClass = (Class<T>) typeArguments[0];
}

Upvotes: 5

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