interfaces can be considered as a blue print or a design of your class.. if you think that these are the methods going to be wrapped and going to be used in your implemented class then you can go for interfaces. and interfaces are best compared to abstract class in general.
abstract classes, if you know certain concrete defnition of your methods, then you have the facility to define it. and as well unknown can be left as such. but the thing is, only one abstract can be extended by a class. since multiple inheritance is not there in
java.
where as interfaces allows you to implement as many interfaces as you wish.