Refactoring, a First Example Vorleak Chy (vorleak.chy@gmail.com) Software Engineer Yoolk Inc http://groups.google.com/group/khmertech/

Before Refactoring Unreadable code Duplicated code Complex code Hard to modify

Unreadable code

Duplicated code

Complex code

Hard to modify

After Refactoring Easier to understand Cheaper to modify Clean code Better code

Easier to understand

Cheaper to modify

Clean code

Better code

Introduction What is Refactoring? Why Refactor?

What is Refactoring?

Why Refactor?

What is Refactoring? The process of changing a software system in such a way that it does not alter the external behaviour of the code, yet improves its internal structure . Fowler, et al., Refactoring, 1999.

The process of changing a software system in such a way that it does not alter the external behaviour of the code, yet improves its internal structure .

Fowler, et al., Refactoring, 1999.

Why Refactor? The reality Extremely difficult to get the design “right” the first time Hard to fully understand the problem domain Hard to understand user requirements, even if the user does! Hard to know how the system will evolve in five years Original design is often inadequate System becomes brittle over time, and more difficult to change

The reality

Extremely difficult to get the design “right” the first time

Hard to fully understand the problem domain

Hard to understand user requirements, even if the user does!

Hard to know how the system will evolve in five years

Original design is often inadequate

System becomes brittle over time, and more difficult to change

Why Refactor? (Cont.) Refactoring helps you to Manipulate code in a safe environment (behavior preserving) Recreate a situation where evolution is possible Understand existing code

Refactoring helps you to

Manipulate code in a safe environment (behavior preserving)

Recreate a situation where evolution is possible

Understand existing code

Look in example So what? Try to understand in the real example

So what?

Try to understand in the real example

The Starting Point

Comments on the Starting Program When you find you have to add a feature to a program, and the program's code is not structured in a convenient way to add the feature, first refactor the program to make it easy to add the feature, then add the feature.

When you find you have to add a feature to a program, and the program's code is not structured in a convenient way to add the feature, first refactor the program to make it easy to add the feature, then add the feature.

The First Step in Refactoring Before you start refactoring, check that you have a solid suite of tests. These tests must be self-checking.

Before you start refactoring, check that you have a solid suite of tests. These tests must be self-checking.

Decomposing and Redistributing the Statement Method (Extract Method) Refactoring changes the programs in small steps. If you make a mistake, it is easy to find the bug. Any fool can write code that a computer can understand. Good programmers write code that humans can understand.

Refactoring changes the programs in small steps. If you make a mistake, it is easy to find the bug.

Any fool can write code that a computer can understand. Good programmers write code that humans can understand.

Moving the Amount Calculation Move Method Replace Temp with Query

Move Method

Replace Temp with Query

Extracting Frequent Renter Points Extract Method

Extract Method

Removing Temps Replace Temp with Query

Replace Temp with Query

Replacing the Conditional Logic on Price Code with Polymorphism Moving methods to movie

Moving methods to movie

At last … Inheritance

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