The document discusses the concept of "Object Calisthenics", which are 9 rules for improving code readability and quality through practices like reducing indentation levels, using early returns, wrapping primitives in classes, and avoiding getters/setters. It provides examples of refactoring code according to these rules, such as extracting methods to reduce indentation, returning early from functions, and replacing getter/setter usage with method calls. References for further reading on Object Calisthenics are also included.

1. Object
Calisthenics
Improve your code following 9 rules
Jeff Bay

2. Jeff Bay
2008

3. How long time do you
spend reading code?

6. How you improve
readability?

7. Where to start?

8. Object Calisthenics

9. One level of indentation
per method
1

10. class Board {
public String board() {
StringBuilder buf = new StringBuilder();
// 0
for (int i = 0; i < 10; i++) {
// 1
for (int j = 0; j < 10; j++) {
// 2
buf.append(data[i][j]);
}
buf.append("n");
}
return buf.toString();
}
}

11. class Board {
public String board() {
StringBuilder buf = new StringBuilder();
// 0
for (int i = 0; i < 10; i++) {
// 1
for (int j = 0; j < 10; j++) {
// 2
buf.append(data[i][j]);
}
buf.append("n");
}
return buf.toString();
}
} Extract Method

12. class Board {
public String board() {
StringBuilder buf = new StringBuilder();
collectRows(buf);
return buf.toString();
}
private void collectRows(StringBuilder buf) {
for (int i = 0; i < 10; i++) {
collectRow(buf, i);
}
}
private void collectRow(StringBuilder buf, int row) {
for (int i = 0; i < 10; i++) {
buf.append(data[row][i]);
}
buf.append("n");
}
}

13. class Board {
public String board() {
StringBuilder buf = new StringBuilder();
// 0
for (int i = 0; i < 10; i++) {
// 1
for (int j = 0; j < 10; j++) {
// 2
buf.append(data[i][j]);
}
buf.append("n");
}
return buf.toString();
}
}
class Board {
public String board() {
StringBuilder buf = new StringBuilder();
collectRows(buf);
return buf.toString();
}
}

14. Don't use ELSE
2

15. public void login(String username, String password) {
if (userRepository.isValid(username, password)) {
redirect("homepage");
} else {
addFlash("error", "Bad credentials");
redirect("login");
}
}

16. Early return
public void login(String username, String password) {
if (userRepository.isValid(username, password)) {
redirect("homepage");
} else {
addFlash("error", "Bad credentials");
redirect("login");
}
}

17. public void login(String username, String password) {
if (userRepository.isValid(username, password)) {
return redirect("homepage");
}
addFlash("error", "Bad credentials");
return redirect("login");
}

18. Wrap all primitives and
Strings in classes
3

19. public void direction(int long, int lat)
{...}

20. public void direction(int long, int lat)
{...}

21. public void direction(Coordinate coordinate)
{...}
public void direction(int long, int lat)
{...}

22. First class collections
4

23. class Board {
public String board() {
StringBuilder buf = new StringBuilder();
collectRows(buf);
return buf.toString();
}
private void collectRows(StringBuilder buf) {
for (int i = 0; i < 10; i++) {
collectRow(buf, i);
}
}
private void collectRow(StringBuilder buf, int row) {
for (int i = 0; i < 10; i++) {
buf.append(data[row][i]);
}
buf.append("n");
}
}

24. One dot per line
5

25. class Board {
public String boardRepresentation() {
StringBuilder buf = new StringBuilder();
for (Location loc : squares()) {
buf.append(loc.current.representation.substring(0, 1));
}
return buf.toString();
}
}

26. class Board {
public String boardRepresentation() {
StringBuilder buf = new StringBuilder();
for (Location loc : squares()) {
buf.append(loc.current.representation.substring(0, 1));
}
return buf.toString();
}
}
class Board {
public String boardRepresentation() {
StringBuilder buf = new StringBuilder();
for (Location location : squares()) {
location.addTo(buf);
}
return buf.toString();
}
}

27. Don’t abbreviate
6

28. public void Coordinate(int long, int lat){...}

29. public void Coordinate(int longitude, int latitude){...}
public void Coord(int long, int lat){...}

30. Keep all classes less
than 50 lines.
7

32. No classes with more
than two instance
variables.
8

33. public void direction(Coordinate coordinate, ...) {...}
public void direction(int long, int lat, string name){...}

34. No getters or setters.
9

35. // Game
private int score;
public void setScore(int score) {
this.score = score;
}
public int getScore() {
return score;
}
// Usage
game.setScore(game.getScore() + ENEMY_DESTROYED_SCORE);

36. // Game
private int score;
public void setScore(int score) {
this.score = score;
}
public int getScore() {
return score;
}
// Usage
game.setScore(game.getScore() + ENEMY_DESTROYED_SCORE);
// Game
public void addScore(int delta) {
score += delta;
}
// Usage
game.addScore(ENEMY_DESTROYED_SCORE);

37. 9 rules
1. One level of indentation per method.
2. Don't use ELSE
3. Wrap all primitives and Strings in classes.
4. First class collections.
5. One dot per line.
6. Don't abbreviate.
7. Keep all classes less than 50 lines.
8. No classes with more than two instance variables.
9. No getters or setters.

38. 38
References

39. 39
References
OBJECT CALISTHENICS
http://williamdurand.fr/2013/06/03/object-calisthenics/
http://www.xpteam.com/jeff/writings/objectcalisthenics.rtf
http://www.pseale.com/linkblogging-object-calisthenics
https://www.youtube.com/watch?v=j6xSGqZoJVI
https://refactoring.com/catalog/extractMethod.html
https://www.youtube.com/watch?v=u-w4eULRrr0
https://pt.slideshare.net/guilhermeblanco/php-para-adultos-clean-code-e-object-calisthenics

41. 41