What should be return type in interface method

Question

I have two classes. Status1 and Status2

these two status has one variable common:

protected A a;

and one which isnt common:

class Status1 {
    protected A a;
    protected ListStatus1.B version;
}

B is static class inside of Status1 class

class Status2 {
    protected A a;
    protected Status2.C version;
}

C is static class inside of Status2 class

so now I want to create interface Status

here I can add variable A . Now I need to add method getVersion which should return static class inside of Status1 / Status2

protected abstract ?? getVersion();

but I dont know what return type should be there

I try to add to this interface static class and this class return but with no succes

Answer 1

The "right way" is to let the two static classes B and C implement a common empty interface , let's call is "Versioned"

public interface Versioned{}

static class B implements Versioned{
...
}
static class C implements Versioned{
...
}

After that, you can write:

 protected abstract Versioned getVersion();

and your method will be allowed to return either B or C.

Answer 2

I think Object should do the trick!

however, while accessing any fields of the object you might face problems. Thus, I suggest you to have an interface Version which is implemented by the inner classes of both the statuses.

Hope this helps,

Cheers

Answer 3

If the difference between Status1.B and Status2.C is essential for your object model, you can make Status generic:

public interface Status<V> {
    public V getVersion();
}

public class Status1 implements Status<Status1.B> {
    public Status1.B getVersion() { ... }
    ...
}

Otherwise you can introduce an interface for both version classes, as suggested by other answers.

Answer 4

One way is to create an interface (let's call it IVersion ) and make both version classes implement that interface. The getVersion() method can then return this interface:

protected abstract IVersion getVersion();