Understanding Java Interfaces in Software Engineering

1. SampleAndroid App Chien-Chung Shen CIS, UD cshen@cis.udel.edu

2. Java Interface • In software engineering, it is important for disparate groups of programmers to agree to a "contract" that spells out how their software interacts • Each group should be able to write their code without any knowledge of how the other group's code is written • Such a contract is termed interfacein Java

3. Example of Driverless Car • Automobile manufacturers write software that operates the car • Electronic guidance instrument manufacturers make computer system that uses GPS and traffic info to drive the car • Neither group needs to know howthe other group's software is implemented as long as they adhere to the published interface

4. An Example Java Interface • public interfaceOperateCar { // constant declarations, if any // methodsignatures intturn(Direction direction, double radius, double startSpeed, double endSpeed); intchangeLanes(Direction direction, double startSpeed, double endSpeed); intsignalTurn(Direction direction, booleansignalOn); intgetRadarFront(double distanceToCar, double speedOfCar); intgetRadarRear(double distanceToCar, double speedOfCar); } • Write a class that implementsthe interface • public class OperateBMW760i implementsOperateCar { // the OperateCar method signatures, with implementation intsignalTurn(Direction direction, booleansignalOn) { // code to turn BMW's LEFT turn indicator lights on // code to turn BMW's LEFT turn indicator lights off ....... } // other members, as needed -- for example, helper classes not // visible to clients of the interface }

5. Interfaces as APIs • Interface is used as an Application Programming Interface (API) • One company sells a software package that contains complex methods that another company wants to use in its own software product – e.g. • One company sells a package of digital image processing methods to companies making end-user graphics programs • The image processing company writes its classes to implement an interface, which it makes public • The graphics company then invokes the image processing methods using the signatures and return types defined in the interface • While API is made public (to its customers), its implementation is kept as a closely guarded secret

6. UI Events • Android provides listeners for events, such as click, touch, etc. • InterfaceTextWatcher – watch for text changes in edit text field • InterfaceOnClickListener– handle click event • ImplementTextWatcher and attachit to the edit text field where user is typing the text • Methods of TextWatcher will be invoked (used) as user changes the text