AOP_英语课件_1.ppt

Aspect-Oriented Programming Definition History What AOP offers to us? An introductory Example Concepts Visitor Pattern Definition Wikipedia: ” Aspect-oriented programming (AOP) is a programming paradigm that increases modularity by allowing the separation of cross-cutting concerns”. AOP does not replace Object-Oriented Programming (OOP), but is an extension of OOP. History History Visitor design pattern motivated to develope AOP. The pattern represent an operation to be performed on the elements of an object structure. Visitor lets you define a new operation without changing the classes of the elements on which it operates. The slides 23-25 present this design pattern. History Gregor Kiczales was one of those who developed CLOS (Common Lisp Object System). He, Jim Des Rivieres and Daniel Bobrow wrote the book The Art of the Metaobject Protocol, which describes the metaobject protocol of CLOS. Later Kiczales and others began to develope AOP according to some priciples of CLOS. The result was AspectJ, the AOP extension to Java. This happened at Xerox PARC. What AOP offers to us? To keep different things as separate. It increases Modularity Dynamics of the program Maintaining Re-usability What AOP offers to us? Practical examples are Error checking and handling Monitoring and logging Contex-sensitive behavior Debugging support Synchronization Multi-object protocols An introductory example Let us suppose that we want to draw a square whose boundary is made of lines. The function squareWithLines() draws this. void squareWithLines() { for(…) { …} // Repeating some code} An introductory example In the same way we can write functions squareWithCircle() and squareWithCrosses(). These functions draw like this: An introductory example In the procedural programming we have to write more functions, if we want to draw also triangles. So we write a function triangleWithLines(). void triangleWithLines() {  for(…) { …} // Draw a triangle} An introductory example In the same wa