I have two classes where one class inherits the other one as given below:

public class UserData {
    protected final String emailAddress;
    protected final String name;

    public UserData(final String emailAddress, final String name) {
        this.emailAddress = emailAddress;
        this.name = name;
    }

    public Optional<String> getEmailAddress() {
        return Optional.ofNullable(this.emailAddress);
    }

    public Optional<String> getName() {
        return Optional.ofNullable(this.name);
    }
}

public class EmployeeData extends UserData {
    protected final String designation;

    public EmployeeData(
            final String emailAddress,
            final String name,
            final String designation
    ) {
        super(emailAddress, name);
        this.designation = designation;
    }

    public Optional<String> getDesignation() {
        return Optional.ofNullable(this.designation);
    }

}

I need to create method in another class that can return either one of these objects and have all getters accessible. I already tried making the return type UserData for both kinds of objects (example given below) but that way, I cannot access the getDesignation getter for EmployeeData. Is there a better way inheritance can be setup to avoid this problem where I cannot access child-specific properties?

public UserData getData() {
    if (...some condition) {
        return new EmployeeData("[email protected]", "myName", "Dev")
    }
    else {
        return new UserData("[email protected]", "myName");
    }
}

I did look into these stackoverflow questions but couldn't quite figure it out for my use case

• C# how to make a function that can return either child or parent class
• What's the equivalent of C# IEnumerable in Java? The covariant-capable one, not the Iterable

CodePudding user response：

Because the object we are returning is of type UserData, we will be unable to call methods that are added within the child class, EmployeeData. You could create the getDesignation() method inside the UserData class and have it return an empty optional object.

public Optional<String> getDesignation() {
    return Optional.empty();
}

In this case, you can now override the method within the EmployeeData class to return designation as an Optional like this,

@Override
public Optional<String> getDesignation() {
    return Optional.ofNullable(this.designation);
}

Now you will have access to the getDestination() method from returned object of getData(), but you will have to be careful and understand that if the returned type is of UserData, then when calling getDesignation() you will be receiving an Optional.empty() object.