Mobile and Context-aware Interactive Systems

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1 Mobile and Context-aware Interactive Systems Gaëlle Calvary Grenoble INP Laboratoire d Informatique de Grenoble (LIG)

2 Core concepts Principles Terminology For more information, see Sara Bouchenak s M1 MOSIG course AOP for HCI Traditional UIs Plastic UIs

Some programming tasks cannot be neatly encapsulated in objects, but must be scattered throughout the code Examples: Logging (tracking program behavior to a file) Profiling (determining where a

3 Some programming tasks cannot be neatly encapsulated in objects, but must be scattered throughout the code Examples: Logging (tracking program behavior to a file) Profiling (determining where a program spends its time) Tracing (determining what methods are called when) Session tracking, session expiration Special security management The result is crosscuting code--the necessary code cuts across many different classes and methods

4 class Fraction { int numerator; int denominator;... public Fraction multiply(fraction that) { traceenter("multiply", new Object[] {that); Fraction result = new Fraction( this.numerator * that.numerator, this.denominator * that.denominator); result = result.reducetolowestterms(); traceexit("multiply", result); return result; Now imagine similar code in every... method you might want to trace

5 Redundant code Difficult to reason about Same fragment of code in many places Non-explicit structure The big picture of the tangling isn t clear Difficult to change Have to find all the code involved......and be sure to change it consistently...and be sure not to break it by accident

6 Separation of concerns Reusable (independent) aspects Weaving

AspectJ is a small, well-integrated extension to Java Based on the 1997 PhD thesis by Christina Lopes, A Language Framework for Distributed Programming AspectJ modularizes crosscutting concerns That

7 AspectJ is a small, well-integrated extension to Java Based on the 1997 PhD thesis by Christina Lopes, A Language Framework for Distributed Programming AspectJ modularizes crosscutting concerns That is, code for one aspect of the program (such as tracing) is collected together in one place The AspectJ compiler is free and open source AspectJ works with JBuilder, Forté, Eclipse, probably others Best online writeup:

8 A join point is a well-defined point in the program flow public class Account { float balance; void credit(float amount) { this.balance += amount; Possible join points: - the execution of the credit method -the access to the balance attribute A pointcut is a selection of join points + the context of execution execution (void Account.credit(float)) - select the join point defined by the execution of the credit method - get context : the targeted object and the parameters

9 An advice is the code to be executed at (before, after, instead of) a pointcut before() : execution (void Account.credit(float)) { System.out.println("About to perform credit operation"); An aspect is a module of code that contains the composition rules to be applied Aspect = pointcuts + advices + ( ) In AspectJ, an aspect is equivalent to a class

10 Design 1. Identify the join points where the behavior must be modified or extended 2. Design the new behavior to be implemented Implementation 1. Write the code of the Aspect 2. Inside the Aspect, write the code of the pointcuts that select the relevant join points 3. Write the code of the advice

11 public class Communicator { public static void print(string message) { System.out.println(message); public static void print(string person, String message) { System.out.println(person + ", " + message); public class Test { public static void main(string[] args) { Communicator.print("Want to learn AspectJ?"); Communicator.print("Tom", "how are you?"); javac Communicator.java Test.java java Test Want to learn AspectJ? Tom, how are you?

12 public aspect HelloAspect { pointcut printcall() : call (void Communicator.print(..)); before() : printcall() { System.out.print("Hello! "); ajc Communicator.java Test.java HelloAspect.java java Test Hello! Want to learn AspectJ? Hello! Tom, how are you?

Aspect-oriented programming (AOP) is a new paradigm--a new way to think about programming AOP is somewhat similar to event handling, where the events are defined outside the code itself AspectJ is

13 Aspect-oriented programming (AOP) is a new paradigm--a new way to think about programming AOP is somewhat similar to event handling, where the events are defined outside the code itself AspectJ is not itself a complete programming language, but an adjunct to Java AspectJ does not add new capabilities to what Java can do, but adds new ways of modularizing the code AspectJ is free, open source software

14 Core concepts Principles Terminology AOP for HCI Traditional UIs Plastic UIs

15 Traditional UIs Plastic UIs Exercise 1: Elicit examples of aspects Exercise 2: Provide examples of aspects at each level of abstraction Exercise 3: Are there issues? Exercise 4: AOP / MDE?

16 Procedural programming Functional programming Proving a theorem by finding values for the free variables Prolog Object-oriented programming (OOP) Evaluating a function defined in terms of other functions Lisp, ML, Ocaml Logic programming Executing a set of commands in a given sequence Fortran, C, Cobol Organizing a set of objects, each with its own set of responsibilities Smalltalk, Java, C++ (to some extent) Aspect-oriented programming (AOP) Executing code whenever a program shows certain behaviors AspectJ (a Java extension) Does not replace O-O programming, but rather complements it

Aspect-Oriented Programming

Aspect-Oriented Programming Harald Gall University of Zurich seal.ifi.uzh.ch/ase Source: http://www.eclipse.org/aspectj/doc/released/progguide/starting-aspectj.html Programming paradigms Procedural programming