My slides from the conference talk "Identifying Code Smells".

1. softwaretester.blog | Benjamin Bischoff
TestCon Europe 2023
Identifying Code Smells

2. softwaretester.blog | Benjamin Bischoff
Law of Two Feet
• If this is not for you, please don’t stay!
• I mean it!
• Really!

3. softwaretester.blog | Benjamin Bischoff
About me
• Benjamin Bischoff
• Test Automation Engineer @ trivago N.V.
• 23 years in IT
• Last 8 years in testing

4. softwaretester.blog | Benjamin Bischoff
I wrote a book
• “Writing API Tests with Karate”
• Available since 05/2023
• Packt Publishing

5. softwaretester.blog | Benjamin Bischoff
I wrote a book
• “Writing API Tests with Karate”
• Available since 05/2023
• Packt Publishing

6. softwaretester.blog | Benjamin Bischoff
Disclaimer
• This is only about identi
fi
cation
• Lots of code
• All Java

7. softwaretester.blog | Benjamin Bischoff
Smelly Code
Smelly code, smelly code
How are they treating you?
Smelly code, smelly code
It’s not your fault.

8. softwaretester.blog | Benjamin Bischoff
The term

9. softwaretester.blog | Benjamin Bischoff
The term

10. softwaretester.blog | Benjamin Bischoff
–Martin Fowler
„A code smell is a surface indication that usually
corresponds to a deeper problem in the system.“

11. softwaretester.blog | Benjamin Bischoff
Why should you care?
• Communication
Speak a common language
• A step towards better code
Clean code principles and design patterns
• Less technical debt
Clean code principles and design patterns
• Testability
Testable code is maintainable code!

12. softwaretester.blog | Benjamin Bischoff
TAXONOMY OF
CODE SMELLS
Mika V. Mäntylä & Casper Lassenius,
Helsinki University of Technology

13. softwaretester.blog | Benjamin Bischoff
TAXONOMY OF
CODE SMELLS
Mika V. Mäntylä & Casper Lassenius,
Helsinki University of Technology

14. softwaretester.blog | Benjamin Bischoff
Classi
fi
cation

15. softwaretester.blog | Benjamin Bischoff
Classi
fi
cation
Bloaters
Long Method
Large Class
Primitive
Obsession
Long Parameter
List
Data Clumps
OOP
Abusers
Switch Statements
Temporary
Field
Refused
Bequest
Alternative classes
with di
ff
erent
Interfaces
Change
Preventers
Divergent Change
Shotgun Surgery
Parallel Inheritance
Hierarchy
Dispensables
Lazy Class
Data Class
Duplicate Code
Dead Code
Speculative
Generality
Couplers
Feature Envy
Inappropriate
Intimacy
Message Chains
Middleman

16. softwaretester.blog | Benjamin Bischoff
Bloaters
Too large to handle.

17. softwaretester.blog | Benjamin Bischoff
public class WebShop {
private final List<Customer> customers = new ArrayList<>();
public String saveCustomer(final Customer customer) {
customers.add(customer);
return String.format(
"We have a new customer called %",
customer.name());
}
}
Bloaters Long Method
A method that does
too much

18. softwaretester.blog | Benjamin Bischoff
public class WebShop {
private final List<Customer> customers = new ArrayList<>();
public String saveCustomer(final Customer customer) {
customers.add(customer);
return String.format(
"We have a new customer called %",
customer.name());
}
}
Bloaters Long Method
A method that does
too much

19. softwaretester.blog | Benjamin Bischoff
public class WebShop {
private final List<Customer> customers = new ArrayList<>();
public String saveCustomer(final Customer customer) {
customers.add(customer);
return String.format(
"We have a new customer called %",
customer.name());
}
}
Bloaters Long Method
A method that does
too much

20. softwaretester.blog | Benjamin Bischoff
public class WebShop {
private final List<Customer> customers = new ArrayList<>();
public String saveCustomer(final Customer customer) {
customers.add(customer);
return String.format(
"We have a new customer called %",
customer.name());
}
}
Bloaters Long Method
A method that does
too much

21. softwaretester.blog | Benjamin Bischoff
public class WebShop {
private final List<Customer> customers = new ArrayList<>();
public String saveCustomer(final Customer customer) {
customers.add(customer);
return String.format(
"We have a new customer called %",
customer.name());
}
}
Bloaters Long Method
A method that does
too much

22. softwaretester.blog | Benjamin Bischoff
public class ShoppingCart {
public void addProduct(final Product product) {}
public void removeProduct(final Product product) {}
public void checkOut() {}
public void enterVoucherCode() {}
public void contactSupport() {}
}
Bloaters Large Class
A class that does too
much

23. softwaretester.blog | Benjamin Bischoff
public class ShoppingCart {
public void addProduct(final Product product) {}
public void removeProduct(final Product product) {}
public void checkOut() {}
public void enterVoucherCode() {}
public void contactSupport() {}
}
Bloaters Large Class
A class that does too
much

24. softwaretester.blog | Benjamin Bischoff
public class ShoppingCart {
public void addProduct(final Product product) {}
public void removeProduct(final Product product) {}
public void checkOut() {}
public void enterVoucherCode() {}
public void contactSupport() {}
}
Bloaters Large Class
A class that does too
much

25. softwaretester.blog | Benjamin Bischoff
public class ShoppingCart {
public void addProduct(final Product product) {}
public void removeProduct(final Product product) {}
public void checkOut() {}
public void enterVoucherCode() {}
public void contactSupport() {}
}
Bloaters Large Class
A class that does too
much

26. softwaretester.blog | Benjamin Bischoff
public class ShoppingCart {
public void addProduct(final Product product) {}
public void removeProduct(final Product product) {}
public void checkOut() {}
public void enterVoucherCode() {}
public void contactSupport() {}
}
Bloaters Large Class
A class that does too
much

27. softwaretester.blog | Benjamin Bischoff
record Customer(
String name,
int age,
String street,
String city,
int zipCode,
String country
) {
}
Bloaters Primitive Obsession
Favouring primitive
data types

28. softwaretester.blog | Benjamin Bischoff
record Customer(
String name,
int age,
String street,
String city,
int zipCode,
String country
) {
}
Bloaters Primitive Obsession
Favouring primitive
data types

29. softwaretester.blog | Benjamin Bischoff
record Customer(
String name,
int age,
String street,
String city,
int zipCode,
String country
) {
}
Bloaters Primitive Obsession
Favouring primitive
data types

30. softwaretester.blog | Benjamin Bischoff
public class CadTool {
public static void main(String[] args) {
int result =
CadTool.calculateResult(13, false, true, -1, null);
}
public static int calculateResult(final int baseValue,
final boolean isMetric,
final boolean is2D,
final int offset,
final Integer height) {
return 0; // some calculation
}
}
Bloaters Long Parameter List
Too many method
parameters

31. softwaretester.blog | Benjamin Bischoff
public class CadTool {
public static void main(String[] args) {
int result =
CadTool.calculateResult(13, false, true, -1, null);
}
public static int calculateResult(final int baseValue,
final boolean isMetric,
final boolean is2D,
final int offset,
final Integer height) {
return 0; // some calculation
}
}
Bloaters Long Parameter List
Too many method
parameters

32. softwaretester.blog | Benjamin Bischoff
public class CadTool {
public static void main(String[] args) {
int result =
CadTool.calculateResult(13, false, true, -1, null);
}
public static int calculateResult(final int baseValue,
final boolean isMetric,
final boolean is2D,
final int offset,
final Integer height) {
return 0; // some calculation
}
}
Bloaters Long Parameter List
Too many method
parameters

33. softwaretester.blog | Benjamin Bischoff
public class CadTool {
public static void main(String[] args) {
int result =
CadTool.calculateResult(13, false, true, -1, null);
}
public static int calculateResult(final int baseValue,
final boolean isMetric,
final boolean is2D,
final int offset,
final Integer height) {
return 0; // some calculation
}
}
Bloaters Long Parameter List
Too many method
parameters

34. softwaretester.blog | Benjamin Bischoff
public class CadTool {
public static void main(String[] args) {
int result =
CadTool.calculateResult(13, false, true, -1, null);
}
public static int calculateResult(final int baseValue,
final boolean isMetric,
final boolean is2D,
final int offset,
final Integer height) {
return 0; // some calculation
}
}
Bloaters Long Parameter List
Too many method
parameters

35. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

36. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

37. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

38. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

39. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

40. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

41. softwaretester.blog | Benjamin Bischoff
record Customer(
String lastName,
String firstName,
String middleName,
String salutation,
String streetAddress,
String city,
String state,
String country,
boolean isEmployed,
boolean isHomeOwner
) {
}
Bloaters Data Clumps
Grouping unrelated
data

42. softwaretester.blog | Benjamin Bischoff
OOP Abusers
Missing object-oriented design possibilities.

43. softwaretester.blog | Benjamin Bischoff
public class Vehicles {
public int numberOfWheels(final String vehicle)
throws Exception {
return switch (vehicle) {
case "car" -> 4;
case "boat" -> 0;
case "bike" -> 2;
case "bicycle" -> 2;
default -> throw new Exception("Unknown");
};
}
}
OOP Abusers Switch Statements
Branching out too
much

44. softwaretester.blog | Benjamin Bischoff
public class Vehicles {
public int numberOfWheels(final String vehicle)
throws Exception {
return switch (vehicle) {
case "car" -> 4;
case "boat" -> 0;
case "bike" -> 2;
case "bicycle" -> 2;
default -> throw new Exception("Unknown");
};
}
}
OOP Abusers Switch Statements
Branching out too
much

45. softwaretester.blog | Benjamin Bischoff
public class Vehicles {
public int numberOfWheels(final String vehicle)
throws Exception {
return switch (vehicle) {
case "car" -> 4;
case "boat" -> 0;
case "bike" -> 2;
case "bicycle" -> 2;
default -> throw new Exception("Unknown");
};
}
}
OOP Abusers Switch Statements
Branching out too
much

46. softwaretester.blog | Benjamin Bischoff
public class Vehicles {
public int numberOfWheels(final String vehicle)
throws Exception {
return switch (vehicle) {
case "car" -> 4;
case "boat" -> 0;
case "bike" -> 2;
case "bicycle" -> 2;
default -> throw new Exception("Unknown");
};
}
}
OOP Abusers Switch Statements
Branching out too
much

47. softwaretester.blog | Benjamin Bischoff
public class Vehicles {
public int numberOfWheels(final String vehicle)
throws Exception {
return switch (vehicle) {
case "car" -> 4;
case "boat" -> 0;
case "bike" -> 2;
case "bicycle" -> 2;
default -> throw new Exception("Unknown");
};
}
}
OOP Abusers Switch Statements
Branching out too
much

48. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

49. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

50. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

51. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

52. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

53. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

54. softwaretester.blog | Benjamin Bischoff
public class Rectangle {
private float sideA;
private float sideB;
public void setSideA(float sideA) {
this.sideA = sideA;
}
public void setSideB(float sideB) {
this.sideB = sideB;
}
public double getAreaSize() {
return sideA * sideB;
}
}
OOP Abusers Temporary Field
Fields that are only
used once

55. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

56. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

57. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

58. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

59. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

60. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

61. softwaretester.blog | Benjamin Bischoff
public class Animals {
interface Animal { void speak(); }
static class Dog implements Animal {
@Override
public void speak() {
System.out.println("Woof");
}
}
static class Fish implements Animal {
@Override
public void speak() {
}
}
}
OOP Abusers Refused Bequest
Passing unneeded
behaviour to classes

62. softwaretester.blog | Benjamin Bischoff
public class Shapes {
record Circle(float radius) {
public double getAreaSize() {
return radius * radius * Math.PI;
}
}
record Rectangle(float a, float b) {
public double getSurfaceSize() {
return a * b;
}
}
}
OOP Abusers Different Interfaces
Confusing naming of
similar functions

63. softwaretester.blog | Benjamin Bischoff
public class Shapes {
record Circle(float radius) {
public double getAreaSize() {
return radius * radius * Math.PI;
}
}
record Rectangle(float a, float b) {
public double getSurfaceSize() {
return a * b;
}
}
}
OOP Abusers Different Interfaces
Confusing naming of
similar functions

64. softwaretester.blog | Benjamin Bischoff
public class Shapes {
record Circle(float radius) {
public double getAreaSize() {
return radius * radius * Math.PI;
}
}
record Rectangle(float a, float b) {
public double getSurfaceSize() {
return a * b;
}
}
}
OOP Abusers Different Interfaces
Confusing naming of
similar functions

65. softwaretester.blog | Benjamin Bischoff
public class Shapes {
record Circle(float radius) {
public double getAreaSize() {
return radius * radius * Math.PI;
}
}
record Rectangle(float a, float b) {
public double getSurfaceSize() {
return a * b;
}
}
}
OOP Abusers Different Interfaces
Confusing naming of
similar functions

66. softwaretester.blog | Benjamin Bischoff
public class Shapes {
record Circle(float radius) {
public double getAreaSize() {
return radius * radius * Math.PI;
}
}
record Rectangle(float a, float b) {
public double getSurfaceSize() {
return a * b;
}
}
}
OOP Abusers Different Interfaces
Confusing naming of
similar functions

67. softwaretester.blog | Benjamin Bischoff
Change Preventers
Hindering further development.

68. softwaretester.blog | Benjamin Bischoff
public class AnimalInformation {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Divergent Change
Changes across
methods

69. softwaretester.blog | Benjamin Bischoff
public class AnimalInformation {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Divergent Change
Changes across
methods

70. softwaretester.blog | Benjamin Bischoff
public class AnimalInformation {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Divergent Change
Changes across
methods

71. softwaretester.blog | Benjamin Bischoff
public class AnimalInformation {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Divergent Change
Changes across
methods

72. softwaretester.blog | Benjamin Bischoff
public class AnimalInformation {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Divergent Change
Changes across
methods

73. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

74. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

75. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

76. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

77. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

78. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

79. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

80. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

81. softwaretester.blog | Benjamin Bischoff
public class Classification {
public static String getLatinName(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return "Equus caballus";
return "";
}
}
public class BodyParts {
public static int getNumberOfLegs(final String animal) {
if (animal.equalsIgnoreCase("horse"))
return 4;
return -1;
}
}
Change Preventers Shotgun Surgery
Changes across
classes

82. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

83. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

84. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

85. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

86. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

87. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

88. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

89. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

90. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

91. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

92. softwaretester.blog | Benjamin Bischoff
public class Birds {
private static class Bird {}
private static class Egg {}
private static class Sparrow extends Bird {
private SparrowEgg layEgg() {
return new SparrowEgg();
}
}
private static class SparrowEgg extends Egg {
}
}
Change Preventers Parallel Hierarchy
Implementing
parallel interfaces

93. softwaretester.blog | Benjamin Bischoff
Dispensables
Unnecessary things that can be removed.

94. softwaretester.blog | Benjamin Bischoff
public class WebShopCheckOut {
public static void checkOut(final ShoppingCart cart) {
// Some implementation
}
}
record ShoppingCart(Product... products) {
}
record Product(String id) {
}
Dispensables Lazy Class
A class with a single
method

95. softwaretester.blog | Benjamin Bischoff
public class WebShopCheckOut {
public static void checkOut(final ShoppingCart cart) {
// Some implementation
}
}
record ShoppingCart(Product... products) {
}
record Product(String id) {
}
Dispensables Lazy Class
A class with a single
method

96. softwaretester.blog | Benjamin Bischoff
public class WebShopCheckOut {
public static void checkOut(final ShoppingCart cart) {
// Some implementation
}
}
record ShoppingCart(Product... products) {
}
record Product(String id) {
}
Dispensables Lazy Class
A class with a single
method

97. softwaretester.blog | Benjamin Bischoff
public class WebShopCheckOut {
public static void checkOut(final ShoppingCart cart) {
// Some implementation
}
}
record ShoppingCart(Product... products) {
}
record Product(String id) {
}
Dispensables Lazy Class
A class with a single
method

98. softwaretester.blog | Benjamin Bischoff
public class WebShopCheckOut {
public static void checkOut(final ShoppingCart cart) {
// Some implementation
}
}
record ShoppingCart(Product... products) {
}
record Product(String id) {
}
Dispensables Lazy Class
A class with a single
method

99. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

100. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

101. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

102. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

103. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

104. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

105. softwaretester.blog | Benjamin Bischoff
public class DataClass {
record Rectangle(int sideA, int sideB) {
}
public static void main(String[] args) {
Rectangle rectangle = new Rectangle(5, 20);
int rectangleArea = rectangle.sideA * rectangle.sideB;
}
}
Dispensables Data Class
Class holding data
but not its own logic

106. softwaretester.blog | Benjamin Bischoff
public class Customers {
private List<Customer> customers;
public void addCustomer(Customer customer) {
customers.add(customer);
customers.forEach(System.out::println);
}
public void removeCustomer(Customer customer) {
customers.remove(customer);
customers.forEach(System.out::println);
}
}
Dispensables Duplicate Code
The same code
multiple times

107. softwaretester.blog | Benjamin Bischoff
public class Customers {
private List<Customer> customers;
public void addCustomer(Customer customer) {
customers.add(customer);
customers.forEach(System.out::println);
}
public void removeCustomer(Customer customer) {
customers.remove(customer);
customers.forEach(System.out::println);
}
}
Dispensables Duplicate Code
The same code
multiple times

108. softwaretester.blog | Benjamin Bischoff
public class Customers {
private List<Customer> customers;
public void addCustomer(Customer customer) {
customers.add(customer);
customers.forEach(System.out::println);
}
public void removeCustomer(Customer customer) {
customers.remove(customer);
customers.forEach(System.out::println);
}
}
Dispensables Duplicate Code
The same code
multiple times

109. softwaretester.blog | Benjamin Bischoff
public class Customers {
private List<Customer> customers;
public void addCustomer(Customer customer) {
customers.add(customer);
customers.forEach(System.out::println);
}
public void removeCustomer(Customer customer) {
customers.remove(customer);
customers.forEach(System.out::println);
}
}
Dispensables Duplicate Code
The same code
multiple times

110. softwaretester.blog | Benjamin Bischoff
public class Customers {
private List<Customer> customers;
public void addCustomer(Customer customer) {
customers.add(customer);
customers.forEach(System.out::println);
}
public void removeCustomer(Customer customer) {
customers.remove(customer);
customers.forEach(System.out::println);
}
}
Dispensables Duplicate Code
The same code
multiple times

111. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

112. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

113. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

114. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

115. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

116. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

117. softwaretester.blog | Benjamin Bischoff
public class DeadCode {
public static void main(String[] args) {
System.out.println("Pi = " + Math.PI);
}
private double getPi() {
return 3.141592;
System.out.println("Returning Pi");
}
}
Dispensables Dead Code
Code that cannot be
reached

118. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

119. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

120. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

121. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

122. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

123. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

124. softwaretester.blog | Benjamin Bischoff
public class LaserPrinter implements Printer {
@Override
public void print(final String textToPrint) {
// Implementation
}
@Override
public void turnOnOrOff() {
//Implementation
}
}
interface Printer {
void print(String textToPrint);
void turnOnOrOff();
}
Dispensables Speculative Generality
Premature future-
proo
fi
ng

125. softwaretester.blog | Benjamin Bischoff
Couplers
Too much or too little coupling.

126. softwaretester.blog | Benjamin Bischoff
public class UsersAndAddresses {
record User(Address address) {
public String getAddressString() {
return
address.street() + ", "
+ address.city() + ", "
+ address.country();
}
}
record Address(String street, String city, String country) { }
}
Couplers Feature Envy
Class implementing
features of another

127. softwaretester.blog | Benjamin Bischoff
public class UsersAndAddresses {
record User(Address address) {
public String getAddressString() {
return
address.street() + ", "
+ address.city() + ", "
+ address.country();
}
}
record Address(String street, String city, String country) { }
}
Couplers Feature Envy
Class implementing
features of another

128. softwaretester.blog | Benjamin Bischoff
public class UsersAndAddresses {
record User(Address address) {
public String getAddressString() {
return
address.street() + ", "
+ address.city() + ", "
+ address.country();
}
}
record Address(String street, String city, String country) { }
}
Couplers Feature Envy
Class implementing
features of another

129. softwaretester.blog | Benjamin Bischoff
public class UsersAndAddresses {
record User(Address address) {
public String getAddressString() {
return
address.street() + ", "
+ address.city() + ", "
+ address.country();
}
}
record Address(String street, String city, String country) { }
}
Couplers Feature Envy
Class implementing
features of another

130. softwaretester.blog | Benjamin Bischoff
public class UsersAndAddresses {
record User(Address address) {
public String getAddressString() {
return
address.street() + ", "
+ address.city() + ", "
+ address.country();
}
}
record Address(String street, String city, String country) { }
}
Couplers Feature Envy
Class implementing
features of another

131. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

132. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

133. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

134. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

135. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

136. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

137. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

138. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

139. softwaretester.blog | Benjamin Bischoff
public class Book {
private final String title;
private Author author;
public Book(String title) { this.title = title;}
public void setAuthor(Author author) { this.author = author; }
}
public class Author {
private final String name;
private Book book;
public Author(String name) { this.name = name; }
public void setBook(Book book) { this.book = book; }
}
Couplers Inappropriate Intimacy
Classes knowing
each other too well

140. softwaretester.blog | Benjamin Bischoff
public class Storehouse {
public static void main(String[] args) {
List<Product> products = List.of(
new Product("Cheese", "Tasty cheese"));
List<Shelf> shelves = List.of(new Shelf(products));
String description =
shelves.get(0).products().get(0).description();
}
record Shelf(List<Product> products) { }
record Product(String name, String description) { }
}
Couplers Message Chains
Returning objects
that return objects…

141. softwaretester.blog | Benjamin Bischoff
public class Storehouse {
public static void main(String[] args) {
List<Product> products = List.of(
new Product("Cheese", "Tasty cheese"));
List<Shelf> shelves = List.of(new Shelf(products));
String description =
shelves.get(0).products().get(0).description();
}
record Shelf(List<Product> products) { }
record Product(String name, String description) { }
}
Couplers Message Chains
Returning objects
that return objects…

142. softwaretester.blog | Benjamin Bischoff
public class Storehouse {
public static void main(String[] args) {
List<Product> products = List.of(
new Product("Cheese", "Tasty cheese"));
List<Shelf> shelves = List.of(new Shelf(products));
String description =
shelves.get(0).products().get(0).description();
}
record Shelf(List<Product> products) { }
record Product(String name, String description) { }
}
Couplers Message Chains
Returning objects
that return objects…

143. softwaretester.blog | Benjamin Bischoff
public record Customer(String name, Address address) {
public String getCity() {
return address.city();
}
public String getStreet() {
return address.street();
}
record Address(String street, String city) { }
}
Dispensables Middle Man
Class accessing
another one on its
behalf

144. softwaretester.blog | Benjamin Bischoff
public record Customer(String name, Address address) {
public String getCity() {
return address.city();
}
public String getStreet() {
return address.street();
}
record Address(String street, String city) { }
}
Dispensables Middle Man
Class accessing
another one on its
behalf

145. softwaretester.blog | Benjamin Bischoff
public record Customer(String name, Address address) {
public String getCity() {
return address.city();
}
public String getStreet() {
return address.street();
}
record Address(String street, String city) { }
}
Dispensables Middle Man
Class accessing
another one on its
behalf

146. softwaretester.blog | Benjamin Bischoff
public record Customer(String name, Address address) {
public String getCity() {
return address.city();
}
public String getStreet() {
return address.street();
}
record Address(String street, String city) { }
}
Dispensables Middle Man
Class accessing
another one on its
behalf

147. softwaretester.blog | Benjamin Bischoff
public record Customer(String name, Address address) {
public String getCity() {
return address.city();
}
public String getStreet() {
return address.street();
}
record Address(String street, String city) { }
}
Dispensables Middle Man
Class accessing
another one on its
behalf

148. softwaretester.blog | Benjamin Bischoff
Classi
fi
cation
Bloaters
OOP
Abusers
Change
Preventers
Dispensables Couplers
Long Method
Large Class
Primitive
Obsession
Long Parameter
List
Data Clumps
Switch Statements
Temporary
Field
Refused
Bequest
Alternative classes
with di
ff
erent
Interfaces
Divergent Change
Shotgun Surgery
Parallel Inheritance
Hierarchy
Lazy Class
Data Class
Duplicate Code
Dead Code
Speculative
Generality
Feature Envy
Inappropriate
Intimacy
Message Chains
Middleman

149. softwaretester.blog | Benjamin Bischoff
Example Code
github.com/bischoffdev/code-smells

150. softwaretester.blog | Benjamin Bischoff
When to tackle code smells?

151. softwaretester.blog | Benjamin Bischoff
Broken window
Long-term effects of un
fi
xed
code.

152. softwaretester.blog | Benjamin Bischoff
YAGNI
Wasting time with future
requirements.

153. softwaretester.blog | Benjamin Bischoff
Campground Rule
Later never comes…

154. softwaretester.blog | Benjamin Bischoff
Code Reviews
Point out smells before it is too
late!

155. softwaretester.blog | Benjamin Bischoff
More information

156. softwaretester.blog | Benjamin Bischoff
Refactoring catalog
refactoring.com/catalog

157. softwaretester.blog | Benjamin Bischoff
Refactoring Guru
refactoring.guru/refactoring

158. softwaretester.blog | Benjamin Bischoff
Marcel Jerzyk
luzkan.github.io/smells/

159. softwaretester.blog | Benjamin Bischoff
Smelly Code
Smelly code, smelly code
How are they treating you?
Smelly code, smelly code
It’s not your fault.

160. softwaretester.blog | Benjamin Bischoff
Thank you!

161. softwaretester.blog | Benjamin Bischoff
Thank you!