How to randomize an object: Map<Author, List<Book>> with EasyRandom in Java?

In order to randomize a Map<Author, List<Book>> using EasyRandom (formerly known as JEasyRandom), you're on the right track by trying to use a MapRandomizer. However, Java's type erasure makes it a bit tricky to directly use types like ArrayList<Book>.class.

Java does not allow ArrayList<Book>.class due to type erasure at runtime, which means generic type information (<Book>) is not available, and thus you cannot directly reference ArrayList<Book>.class.

A workaround for this is to create a new randomizer class that extends ListRandomizer<Book>, and then use it with the MapRandomizer. Here's how you can approach it:Create a Custom List Randomizer,You need a randomizer for List<Book> that EasyRandom can use. Since you can't directly specify List<Book>.class, you create a subclass of ListRandomizer<Book> for this purpose. Use the Custom List Randomizer with MapRandomizer: Once you have a custom randomizer for List<Book>, you can use it with MapRandomizer to generate your Map<Author, List<Book>>.

Here's an example implementation:

import org.jeasy.random.EasyRandom;
import org.jeasy.random.api.Randomizer;
import org.jeasy.random.randomizers.collection.ListRandomizer;
import org.jeasy.random.randomizers.misc.EnumRandomizer;
import java.util.ArrayList;
import java.util.List;
import java.util.Map;

public class Main {

    public static void main(String[] args) {
        // Initialize EasyRandom
        EasyRandom easyRandom = new EasyRandom();

        // Custom ListRandomizer for List<Book>
        Randomizer<List<Book>> booksRandomizer = () -> new ListRandomizer<>(() -> easyRandom.nextObject(Book.class), 5).getRandomValue();

        // MapRandomizer using the custom ListRandomizer for the value
        MapRandomizer<Author, List<Book>> mapRandomizer = new MapRandomizer<>(() -> easyRandom.nextObject(Author.class), booksRandomizer);

        // Generate the random Map<Author, List<Book>>
        Map<Author, List<Book>> randomMap = mapRandomizer.getRandomValue();

        // Output the generated map
        System.out.println(randomMap);
    }
}

In this example:

• easyRandom.nextObject(Author.class) is used to generate random Author instances.
• booksRandomizer is a custom Randomizer for List<Book>, utilizing ListRandomizer to generate lists of random Book objects. You can adjust the 5 to control the number of books in each list.
• Finally, mapRandomizer combines these to generate a Map<Author, List<Book>>.

Ensure you have defined the Author and Book classes according to your requirements. Also, adjust the randomization logic inside the lambda expressions as needed for your specific use case.