Object Oriented Programming, Slides of Object Oriented Programming

Download Object Oriented Programming and more Slides Object Oriented Programming in PDF only on Docsity! 1 Refactoring » What is Refactoring?  Refactoring is the process of changing a software system so that  the external behavior is not altered, but  the internal structure is improved.  Refactoring (http://www.refactoring.com/) is a “behavior-preserving transformation.”  Small changes per transformation   less likely to go wrong  System works after each change 2 Refactoring » Why Refactoring?  Methods might no longer do (only) what their name suggests.  Functionality that should be in two different classes might be in the same class.  Functionality that should be in one class might be duplicated in two or more classes.  Improve the design of existing code.  Gain a better understanding of the code. 5 Refactoring » Example  Better: Changing the name of the method (for example, calculateCustomerCharge).  What else do we need to do to solve the problem?  We also need to change the name at all call sites.  We need to update the documentation.  If this method overrides a method in another class, the other name may need to be changed too. Ditto if this method implements an interface.  This is known as the Rename Method refactoring. 6 Refactoring » Example  Let’s refactor our getRoomCharge() method. public double calculateCustomerCharge() { double roomCharge = getRoomCharge(); double incidentals = getIncidentals(); double tax = getTax(roomCharge, incidentals); return roomCharge + incidentals + tax; }  What have we done?  We defined additional methods to compute incidentals, tax, etc.  In order to do this, we added local variables for the quantities that are being calculated in the new methods.  Some pre-existing local variables ended up being parameters to the new method.  The returned value is different from what was returned in the pre- existing method. 7 Refactoring » Common Refactorings  Rename  Methods, Fields, Packages, Projects, Parameters, or Local Variables  Encapsulate Field (generate getter and setter)  Pull up a Field or Method (into superclass)  Push down a Field or Method (into subclass)  Extract Method, Local Variable, or Constant from an Expression  Change Method Signature