public class GetActivity
{
    ChildClass childclass;

    @Inject
    public GetActivity(ChildClass childClass)
    {
        this.childClass = childclass;
    }
    String id = childClass.get(id);
    ....
}

public class SaveActivity
{
    ChildClass childclass;

    @Inject
    public SaveActivity(ChildClass childClass)
    {
        this.childClass = childclass;
    }
    childClass.save(id);
    ....
}

public interface ChildClass
{
    String get(id);
    void save(id);
}

public class ChildClassImpl implements ChildClass
{
    String storage;

    public ChildClassImpl(String storage)
    {
        this.storage =storage;
    }

    String get(Id)
    {
       someOtherObject.get(id, storage);
    }

    void save(id)
    {
       someOtherObject.save(id, storage);
    }
}

public class ChildClassProvider1 implements Provider<ChildClass>
{
    @Override
    public ChildClass get()
    {
      ChildClass childClass = new ChildClass("hello");
    }
}

public class ChildClassProvider2 implements Provider<ChildClass>
{
    @Override
    public ChildClass get()
    {
      ChildClass childClass = new ChildClass("secondHello");
    }
}