How can we create a class forName if the class is Generic type

Question

        class A<B> {
            ...
        }
    
    Class<A<B>> a = Class.forName(A.class.getTypeName()) throws error 

 a.getDeclaredConstructor(String.class).newInstance("hello world")

what should I do to make an Instance for this class?

I want to know how I can make class Name with generic type this example does not work

other example

public class SimpleTest {

    interface TakePhoto<B> {
        TakePhoto<B> clickShutter();

        B done();
    }

    public @interface Specific {
        String value();
    }

    @Specific("GALAXY-S5")
    static class GalaxyS5TakePhoto<B> implements TakePhoto<B>{
        
        B backPage;

        GalaxyS5TakePhoto(B backPage){
            this.backPage = backPage;
        }

        @Override
        public TakePhoto<B> clickShutter() {
            //...
            return this;
        }

        @Override
        public B done() {
            return backPage;
        }
    }

    @Test
    public void Test() {
        // if a Device is Galaxy S5, I want to make GalaxyS5TakePhoto 
        // if the device is other I will have other class models and make its instance 
        // I have package of these classes and want to make right instance. 
        
        // first collect specific classes which have TakePhoto
        // then find and filter specific model
        // then create new Instance 
    }
}

I just want to make class with Generic type

first collect specific classes which have TakePhoto then find and filter specific model then create new Instance

Can you show how would you create an instance of `A` without reflection? — Sweeper, Mar 04 '21 at 02:55
Do you have a class called `B`? Otherwise creating a `A` doesn't make much sense... — Sweeper, Mar 04 '21 at 02:56
I have edited first post could you please look at it one more time ? — Genad Papashvili, Mar 04 '21 at 03:24

score 0 · Answer 1 · answered Mar 04 '21 at 03:02

You cannot because generic information is removed at runtime, there is only class A there.

However, you can create a seperate class like

public class M extends A<B> {
}

Class M will hold the generic information.

Now here is a full demonstration on how to extract generic information from a Class object:

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;
import java.util.ArrayList;

public class GenericInfoInClass {

    // class which contains generic information
    public static class StringList
            extends ArrayList<String>
            implements Comparable<StringList>
    {

        @Override
        public int compareTo(StringList o) {
            return 0;
        }
    }

    public static void main(String[] args) {
        Type[] genericInterfaces = StringList.class.getGenericInterfaces();
        for (Type genericInterface : genericInterfaces) {
            System.out.println(genericInterface);
            System.out.println("[Generic type arguments:]");

            ParameterizedType parameterizedType = (ParameterizedType) genericInterface;
            Type[] genericTypes = parameterizedType.getActualTypeArguments();
            for (Type genericType : genericTypes) {
                System.out.println("  -- " + genericType);
            }
        }

        System.out.println("----------------------------");

        Type genericSuperclass = StringList.class.getGenericSuperclass();
        System.out.println(genericSuperclass);
        System.out.println("[Generic type arguments:]");

        ParameterizedType parameterizedType = (ParameterizedType) genericSuperclass;
        Type[] genericTypes = parameterizedType.getActualTypeArguments();
        for (Type genericType : genericTypes) {
            System.out.println("  -- " + genericType);
        }
    }
}

I updated first post please look once again – Genad Papashvili Mar 04 '21 at 03:28 — Genad Papashvili, Mar 04 '21 at 03:28

How can we create a class forName if the class is Generic type

1 Answers1