Software Engineering for Self-Directed Learners
  • Refactoring

    What

    Can explain refactoring

    The first version of the code you write may not be of production quality. It is OK to first concentrate on making the code work, rather than worry over the quality of the code, as long as you improve the quality later. This process of improving a program's internal structure in small steps without modifying its external behavior is called refactoring.

    • Refactoring is not rewriting: Discarding poorly-written code entirely and re-writing it from scratch is not refactoring because refactoring needs to be done in small steps.
    • Refactoring is not bug fixing: By definition, refactoring is different from bug fixing or any other modifications that alter the external behavior (e.g. adding a feature) of the component in concern.

    💡 Improving code structure can have many secondary benefits: e.g.

    • hidden bugs become easier to spot
    • improve performance (sometimes, simpler code runs faster than complex code because simpler code is easier for the compiler to optimize).

    Given below are two common refactorings (more).

    Refactoring Name: Consolidate Duplicate Conditional Fragments

    Situation: The same fragment of code is in all branches of a conditional expression.

    Method: Move it outside of the expression.

    Example:

         
    if (isSpecialDeal()) {
        total = price * 0.95;
        send();
    } else {
        total = price * 0.98;
        send();
    }
    

     → 
    if (isSpecialDeal()){
        total = price * 0.95;
    } else {
        total = price * 0.98;
    }
    send();
    
    

         
    if is_special_deal:
        total = price * 0.95
        send()
    else:
        total = price * 0.98
        send()
    

     → 
    if is_special_deal:
        total = price * 0.95
    else:
        total = price * 0.98
        
    send()
    

    Refactoring Name: Extract Method

    Situation: You have a code fragment that can be grouped together.

    Method: Turn the fragment into a method whose name explains the purpose of the method.

    Example:

    void printOwing() {
        printBanner();
    
        //print details
        System.out.println("name:	" + name);
        System.out.println("amount	" + getOutstanding());
    }
    

    void printOwing() {
        printBanner();
        printDetails(getOutstanding());
    }
    
    void printDetails (double outstanding) {
        System.out.println("name:	" + name);
        System.out.println("amount	" + outstanding);
    }
    
    def print_owing():
        print_banner()
    
        //print details
        print("name:	" + name)
        print("amount	" + get_outstanding())
    

    def print_owing():
        print_banner()
        print_details(get_outstanding())
    
    def print_details(amount):
        print("name:	" + name)
        print("amount	" + amount)
    

    💡 Some IDEs have built in support for basic refactorings such as automatically renaming a variable/method/class in all places it has been used.

    Refactoring, even if done with the aid of an IDE, may still result in regressions. Therefore, each small refactoring should be followed by regression testing.

    Choose the correct statements

    • a. Refactoring can improve understandability
    • b. Refactoring can uncover bugs
    • c. Refactoring can result in better performance
    • d. Refactoring can change the number of methods/classes

    a, b, c, d

    Explanation:

    • (a, b, c) Although the primary aim of refactoring is to improve internal code structure, there are other secondary benefits.
    • (d) Some refactorings result in adding/removing methods/classes.

    Do you agree with the following statement? Justify your answer.

    Statement: Whenever we refactor code to fix bugs, we need not do regression testing if the bug fix was minor.

    There are two flaws in the given statement.

    DISAGREE.

    1. Even a minor change can have major repercussions on the system. We MUST do regression testing after each change, no matter how minor it is.
    2. Fixing bugs is technically not refactoring.

    Explain what is refactoring and why it is not the same as rewriting, bug fixing, or adding features.

    How

    Can apply some basic refactoring

    Given below are some more commonly used refactorings. A more comprehensive list is available at refactoring-catalog .

    1. Consolidate Conditional Expression
    2. Decompose Conditional
    3. Inline Method
    4. Remove Double Negative
    5. Replace Magic Number with Symbolic Constant
    6. Replace Nested Conditional with Guard Clauses
    7. Replace Parameter with Explicit Methods
    8. Reverse Conditional
    9. Split Loop
    10. Split Temporary Variable

    When

    Can decide when to apply a given refactoring

    We know that it is important to refactor frequently so as to avoid the accumulation of ‘messy’ code which might get out of control. But how much refactoring is too much refactoring? It is too much refactoring when the benefits no longer justify the cost. The costs and the benefits depend on the context. That is why some refactorings are ‘opposites’ of each other (e.g. extract method vs inline method).

    ‘Extract method’ and ‘Inline method’ refactorings

    a