CSC/ECE 517 Fall 2010/ch2 S20 CR
Introduction to Code Reuse
Advantages of Code Reuse
Disadvantages of Code Reuse
Categories of Code Reuse
Internal Code Reuse
Suppose a team needs to start a new project.In order to start the project the team can use all possible reusable components that it has built earlier instead of again re-creating them.Such usage of reusable components is referred as Internal Code Reuse.Few such examples of Internal Code reuse are :
Simple Copy and Paste of the Code
Here we simply try to find the source code that perform the required functionality.We copy and paste the source code into our required code area.But in this case people sometimes try to copy from an external source which is discouraged method and it leads to plagiarism.
Using Software Library
It is the most common example of code reuse.Suppose we want certain manipulating functions like date,time,string or functions related to interfacing of an external database with our program we use software libraries.These libraries are either created by us or these comes as external library in the languages.The code reuse in various languages are.
- Examples of code reuse in C/C++
If we want to use all string functionality we can include string header and call the required method in our code area.
#include "stdio.h" #include "string.h" //Inclusion of string header file int main() { if (strcmp("ncsucsc517","ncsucsc517")== 0) //strcmp is function provided by string library which compares two string. { printf("the string are same"); } return 0; }
We can also create Macro and reuse it.Following example clearly explains it.
#include "stdio.h" #define Cubeof(x) x*x*x //Here at first we define a Macro that calculates the cube of a number int main() { int input = 6; printf("\nCubeof(x)=%i",Cubeof(input)); //Here we reuse the Macro "Cubeof" return 0; }
In addition to above C++ also provides Standard Template Libraries(STL).Few STL libaries are
1.Container Library - Bitset,Dequeue,List,Map,Vector
2.Iterator Library - Iterator
- Examples of code reuse in Java
In Java we use Packages for code reuse.A Package is collection of related files for a particular functionality and usability.Generally a package contains classes,interfaces etc.For example if we want to print todays date we can use Date Class provided by java.util package.Sample example illustrates it.
The example of a class inside a package.
java.util.Date today = new java.util.Date();//java.util is a package which contains Date Class System.out.println("Todays Date is "+today);
The example of an Interface inside a package.
interface powerOf { public void squareOf(int number); } public class calculator implements powerOf { public void squareOf(int number) { int result; result = number * number; System.out.println("The square of the number is"+result); } public static void main(String args[]) { calculator obj = new calculator(); obj.squareOf(20); } }
- Examples of code reuse in Ruby
In Ruby the code reuse is mainly done through usage of modules and mixins. The example of Module is
module Power NUMBER = 5 def Power.Square(x) return x*x end def Power.Cube(x) return x*x*x end end cube = Power.Cube(Power::NUMBER) puts cube
The example of Mixin is
class Calculator include Power //We have included the module created above def square_of_number number puts Power.Square(number) //Reusing the code end end obj = Calculator.new obj.square_of_number 20
External Code reuse
External code reuse refers to the usage of a Third party Licensed Tool ,applications or framework.Either they come with certain cost or they are open source.
Some of the examples of external code reuse are
Frameworks
Ruby on Rails (RoR) is an open Source Web Application framework.It is used for rapid creation of web application and it uses agile methodologies.It provides various packages like
1.ActiveRecord
- It is used as object relational mapping with database
- It is used as object relational mapping with database
2.ActiveResource
- It provides webservice
- It provides webservice
3.Actionpack
- It splits the response to a web request into two part.One goes to controller and another goes to view
- It splits the response to a web request into two part.One goes to controller and another goes to view
4.ActiveSupport
- It is the collection of utility classes and standard library extensions
- It is the collection of utility classes and standard library extensions
5.ActionController
- It acts as middle man between model and view.It routes the request of view to model by acting on request for save or update.Also it renders data from model to view.