When I have `Serializable` in a class, do I need to add `Serializable` to all my objects within the class?

For example,

```
public class User implements Serializable{

private List<Role> role;
private Task task;
}

```

Do I need to add `Serializable` to `Role` and `Task`, too?

```
public class Task implements Serializable{
    // ...
}

public class Role implements Serializable{
    // ...
}

```