Introduction

Refactoring

Easy example (before)

public boolean max(int a, int b) {
    if(a > b) {
        return true;
    } else if (a == b) {
        return false;
    } else {
        return false;
    }
}

Easy example (after)

public boolean max(int a, int b) {
     return a > b;
}

Why ?

  • Improve understanding of code

  • Help find and fix bugs

  • Accelerate the speed of development

  • Improve design

Code smells (basic)

  • Large class

  • Long methods

  • Too many parameters

  • Using a lot of primitive data types (String, float, …​)

Code smells (OO)

  • Switch case

  • Temporary field (null)

  • Parallel inheritance hierarchies

  • Wrong use of inheritance

Use of inheritance

OK

Wrong use of inheritance

NOK

Garbage Smells

  • Too many comments

  • Duplicated code

  • Lazy class

  • Unused code

Excessive connectivity

  • External methods

  • Dependency with another class' implementation details

  • Long class call

Refactoring techniques

  • Extract a class

  • Extract a method

  • Passing an entire object

Extract a class

class Human {
    private String name;
    private String age;
    private String country;
    private String city;
    private String street;
    private String house;
    private String quarter;

    public String getFullAddress() {
        StringBuilder result = new StringBuilder();
        return result
                        .append(country)
                        .append(", ")
                        .append(city)
                        .append(", ")
                        .append(street)
                        .append(", ")
                        .append(house)
                        .append(" ")
                        .append(quarter).toString();
    }
 }

!

class Human {
   private String name;
   private String age;
   private Address address;

   private String getFullAddress() {
       return address.getFullAddress();
   }
}
class Address {
   private String country;
   private String city;
   private String street;
   private String house;
   private String quarter;

   public String getFullAddress() {
       StringBuilder result = new StringBuilder();
       return result
                       .append(country)
                       .append(", ")
                       .append(city)
                       .append(", ")
                       .append(street)
                       .append(", ")
                       .append(house)
                       .append(" ")
                       .append(quarter).toString();
   }
}

Extract a method

public void calcQuadraticEq(double a, double b, double c) {
    double D = b * b - 4 * a * c;
    if (D > 0) {
        double x1, x2;
        x1 = (-b - Math.sqrt(D)) / (2 * a);
        x2 = (-b + Math.sqrt(D)) / (2 * a);
        System.out.println("x1 = " + x1 + ", x2 = " + x2);
    }
    else if (D == 0) {
        double x;
        x = -b / (2 * a);
        System.out.println("x = " + x);
    }
    else {
        System.out.println("Equation has no roots");
    }
}

!

public void calcQuadraticEq(double a, double b, double c) {
    double D = b * b - 4 * a * c;
    if (D > 0) {
        dGreaterThanZero(a, b, D);
    }
    else if (D == 0) {
        dEqualsZero(a, b);
    }
    else {
        dLessThanZero();
    }
}

Passing an entire object

public void employeeMethod(Employee employee) {
    // Some actions
    double yearlySalary = employee.getYearlySalary();
    double awards = employee.getAwards();
    double monthlySalary = getMonthlySalary(yearlySalary, awards);
    // Continue processing
}

public double getMonthlySalary(double yearlySalary, double awards) {
     return (yearlySalary + awards)/12;
}

!

public void employeeMethod(Employee employee) {
    // Some actions
    double monthlySalary = getMonthlySalary(employee);
    // Continue processing
}

public double getMonthlySalary(Employee employee) {
    return (employee.getYearlySalary() + employee.getAwards())/12;
}

Advice for the project

Issues to list the ideas

issues

Describe / Explain each idea

issueExample

1 refactoring = 1 branch

git flow jmb

Professional README

exempleProjet2020.pdf

Ressources

Ready for a quiz?

make refa