This is my solution. Please review and accept this if it looks good. Thanks!
The mixed business-entity class is re-used as a wrapper class. This makes it possible to re-use this in all implementing classes where no changes are needed.
public final class Language Extends LanguageImpl{
private final LanguageEntity languageEntity;
//Constructor
public Language(LanguageEntity le) {
languageEntity = le;
}
//Wrapper method
public static Language findByUser(User user) {
LanguageEntity le = findEntityByUser(user);
Language language = new Language(le);
return language;
}
....
}
A new Entity class is created (LanguageEntity) in a new package. This avoids package and naming conflicts with the original mixed class (Language). All entity fields and methods from the mixed class are moved here.
package com.test.entity;
public final class LanguageEntity {
private final Long id;
private final String code;
private final String description;
//Constructor
public LanguageEntity() { }
//getters and setters
public String getId() { return this.id; }
public void setId(Long id) { this.id = id; }
...
}
A new business class is created (LanguageImpl) in a new package. All business methods are moved here. The original mixed class will extend this new business class.
package com.test.impl
public final class LanguageImpl {
//Constructor
public LanguageImpl() { }
//Business is a part of this class
public static LanguageEntity findEntityByUser(User user) {
LanguageEntity language;
...implementation to find user language...
return language;
}
....
}
This is an implementing class that does not need changes. Hundreds of implementation locations remain unchanged, which saves a lot of work. Hurray!
public class Messenger {
public Messenger() { }
public static void sendEmail() {
...
Language emailLanguage = Language.findByUser(user):
...
}
}
And for future development, the new combination LanguageEntity and LanguageImpl will be used. The original Language will be deprecated.
Please leave comments on this solution. Other solutions are more than welcome!