public class Item {
    private final String id;

    public Item(String id) {
        this.id = id;
    }

    public String getId() {
        return id;
    }
}

//simplified example: the main use case of the library is to map different types to another
Mapper<Item, Item> mapper = new ConstructorBuilder1<Item, String, Item>(Item::new)
            .from(Item::getId).mapTo(Function.identity())
            .build();