1. Refactoring Constants and Variables Lesson Three: Constants and Variables

2. Refactoring Constants and Variables Process 1. Review scope of all constants 2. Review scope of all variables 3. Adjust any gets/sets due to reviews 4. Apply refactorings

3. Refactoring Constants and Variables 1. Review the scope of all constants 2. Review the scope of all variables 3. Adjust code to limit scope A.Review all the constants and variables to make sure they are not MORE global in scope than necessary. Downcast any that are too broad in scope. Adjust gets and sets to adapt to new or modified scope.

4. Refactoring Constants and Variables 3. Adjust code to limit scope Investigate variables, parameters, and methods to see if they can be local or need to be uplifted to later evaluate their partitioning into classes. 1 2 3

5. Refactoring Constants and Variables 3. Adjust code to limit scope private static int mostStrategicMove[] = {4,0,2,6,8,1,3,5,7}; // square order of importance BECOMES int mostStrategicMove[] = {4,0,2,6,8,1,3,5,7};// square order of importance // in the method bestMove

6. Refactoring Constants and Variables 4.Apply Refactorings Replace Magic Number with Symbolic Constant Introduce Explaining Variable Split Temporary Variable Replace Temp with Query Separate Query from Modifier **** Replace Array with Object *****

7. Refactoring Constants and Variables Summary: You have a literal number with a particular meaning Create a constant, name it after the meaning, and replace the number with it. Replace Magic Number with Symbolic Constant

8. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: Motivation: Magic numbers are numbers with special values that usually are not obvious. Add a constant to store the values of these magic numbers.

9. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: Example: double potentialEnergy (double mass, double height) { return mass * 9.81 * height; }// end potential Energy double potentialEnergy (double mass, double height { return mass * GRAVITATIONAL_CONSTANT * height; }// end potentialEnergy static Final double GRAVITATIONAL_CONSTANT * 9.81; Should be

10. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: Mechanics: declare a constant and set to magic number find occurrences of magic number if magic matches constant usage – use constant when all magic numbers changed compile and test.

11. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: static final int ENDINGSTATE = (1 << 9) - 1; BECOMES static final int NINE_SHIFTING_BITS = 9; static final int ENDINGSTATE = (1 << NINE_SHIFTING_BITS) - 1; for (int i = 0 ; i < 9 ; i++) { // for square = 0 to < 9 BECOMES static final int firstCell = 0; // first cell at row 1 col 1 static final int lastCell = 8; // last cell at row 3, col 3 for (int i = firstCell ; i <= lastCell ; i++) { \

12. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: int bestmove = -1; if (bestmove == -1) { if (bestmove != -1) { return -1; // return no more moves BECOMES static final int bestMoveNotFound = -1; //indicating best move not found int bestmove = bestmoveNotFound; if (bestmove == bestMoveNotFound) { if (bestmove != bestMoveNotFound) { return bestMoveNotFound; // return no more moves

13. Refactoring Constants and Variables Replace Magic Number with Symbolic Constant: for (int row = 0 ; row < 3 ; row++) { for (int col = 0 ; col < 3 ; col++, i++) { int col = (x * 3) / d.width;// determine col int row = (y * 3) / d.height; // determine the row BECOMES static final int NUMBER_OF_COLUMNS = 3; static final int NUMBER_OF_ROWS = 3; for (int row = 0 ; row < NUMBER_OF_ROWS ; row++) { for (int col = 0 ; col < NUMBER_OF_COLUMNS ; col++, i++) { int col = (x * NUMBER_OF_COLUMNS) / d.width;// determine col int row = (y * NUMBER_OF_ROWS) / d.height; // determine the row

14. Refactoring Constants and Variables Summary: You have a complicated expression. Put the result of the expression in a temp with a name that explains the purpose. 4. Introduce Explaining Variable

15. Refactoring Constants and Variables 4. Introduce Explaining Variable: Motivation: Complex code that requires many lines of code but could more easily be explained with some variable name that helps to explain the code semantics.

16. Refactoring Constants and Variables 4. Introduce Explaining Variable: Example: If ( (platform.toUpperCase().indexOf(“MAC”) > -1) && (browser.toUpperCase().indexOf(“IE”) > -1) && wasInitialized () && resize >0) { ….. other code …..} goes to final boolean isMacOs = platform.toUpperCase().indexOf(“MAC”) > -1; final boolean isIEBrowser = platform.toUpperCase().indexOf(“IE”) > -1; final boolean wasResized = resize >0; If (isMacOs && isIEBrowser && wasInitialized () && was Resized) { ….. other code …..}

17. Refactoring Constants and Variables 4. Introduce Explaining Variable: Mechanics: declare a final temp variable set it to the result portion of the expression compile and test

18. Refactoring Constants and Variables Summary: You have one temp assigned to more than once and it is not a loop variable. Make a new temp for each assignment 5. Split Temporary Variables

19. Refactoring Constants and Variables 5. Split Temporary Variables: Motivation: Looping variables (control variables of a loop) or accumulator variables (summing variables) may have the need for assignments more than once. Other variables should not be assigned to more than once. Investigation of greater than one assignments to the same variable may yield variables that are actually used for different semantics.

20. Refactoring Constants and Variables 5. Split Temporary Variables: Example: double getDistanceTravelled (int time) { double result; double acc = _primaryForce / _mass; // initial value of acceleration of first force int primaryTime = Math.min(time, _delay); result = 0.5 * acc * primaryTime * primaryTime; int secondaryTime = time - _delay; if (secondaryTime > 0) { double primaryVel = acc * _delay; acc = (_primaryForce * _secondaryForce) / _mass; // final value of acceleration result += primaryVel * secondaryTime + 0.5 *acc * secondaryTime * secondaryTime; } // end if return result; } // end getDistanceTravelled

21. Refactoring Constants and Variables 5. Split Temporary Variables: Example: double getDistanceTravelled (int time) { double result; double primaryacc = _primaryForce / _mass; // initial value of acceleration of first force int primaryTime = Math.min(time, _delay); result = 0.5 * primaryacc * primaryTime * primaryTime; int secondaryTime = time - _delay; if (secondaryTime > 0) { double primaryVel = acc * _delay; double acc = (_primaryForce * _secondaryForce) / _mass; // final value of acceleration result += primaryVel * secondaryTime + 0.5 *acc * secondaryTime * secondaryTime; } // end if return result; } // end getDistanceTravelled CAN YOU THINK OF OTHER REFACTORING?

22. Refactoring Constants and Variables 5. Split Temporary Variables: Mechanics: find the variables assigned to more than once change the name for each different assignments change references compile and test

23. Refactoring Constants and Variables Summary: You are using a temporary variable to hold the result of an expression. Extract the expression into a method Replace all references to the temp with the expression. 3. Replace Temp with Query

24. Refactoring Constants and Variables 3. Replace Temp with Query: Motivation: Methods with many temps tend to be long. Replacing the temp variable with a query method makes the code cleaner for further refactoring.

25. Refactoring Constants and Variables 3. Replace Temp with Query: Example: double getPrice(){ int basePrice = _quanity * itemPrice; double discountFactor; if (basePrice > 1000) discountFactor = 0.95 else discountFactor = 0.98; return basePrice *discountFactor; }// end getPrice

26. Refactoring Constants and Variables 3. Replace Temp with Query: Example: double getPrice(){ int basePrice = _quanity * itemPrice; double discountFactor; if (basePrice() > 1000) discountFactor = 0.95 else discountFactor = 0.98; return basePrice() *discountFactor; }// end getPrice private int basePrice () { return quanity * itemPrice; }

27. Refactoring Constants and Variables 3. Replace Temp with Query: Example: double getPrice(){ double discountFactor = discountFactor(); if (basePrice() > 1000) discountFactor = 0.95 else discountFactor = 0.98; return basePrice() *discountFactor; }// end getPrice private double discountFactor () { if (basePrice() > 1000) return 0.95; else return 0.98; } // end discountFactor Extract Method

28. Refactoring Constants and Variables 3. Replace Temp with Query: Example: double getPrice(){ double discountFactor = discountFactor(); return basePrice() *discountFactor; }// end getPrice private double discountFactor () { if (basePrice() > 1000) return 0.95; else return 0.98; } // end discountFactor private int basePrice () { return quanity * itemPrice; } Can I do more? Replace Temp with Query

29. Refactoring Constants and Variables 3. Replace Temp with Query: Mechanics: declare the temp as final to check references compile to test extract the right hand side as a method body if a loop take entire loop name and construct the method replace the temp with the call

30. Refactoring Constants and Variables 3. Replace Temp with Query: int best = bestMove(computerStatus, userStatus); setComputerStatus (computerStatus | 1 << best); BECOMES setComputerStatus (computerStatus | 1 << bestMove(computerStatus, userStatus));

31. Refactoring Constants and Variables Summary: You have an array in which certain elements mean different things. Replace the array with an object that has a field for each element. Replace Array with Object

32. Refactoring Constants and Variables Replace Array with Object: Motivation: You have a collection of objects BUT those objects are not similar. Arrays should not be composed of objects not similar. Replace the dissimilar array with an object.

33. Refactoring Constants and Variables Replace Array with Object: Example: String[] row = new String[3]; row [0] = “Liverpool”; row [1] = ’13”; String name = row(0); int wins = Integer.parseInt(row(1)); The original array. Code using the array.

34. Refactoring Constants and Variables Replace Array with Object: Example: class Performance {} row._data[0] = “Liverpool”; row._data [1] = ’13”; String name = row._data(0); int wins = Integer.parseInt(row._data(1)); Create and access the array.

35. Refactoring Constants and Variables Replace Array with Object: Example: class Performance {} public String getName() { return _data[0]; public void setName (String arg) {_data[0] = arg; } String name = row.getName(); int wins = Integer.parseInt(row._data[1]); private String [].data = new String[3]; Add getters and setters. Make the array private.

36. Refactoring Constants and Variables Replace Array with Object: Example: class Performance {} public String getName() { return _name; public void setName (String arg) {_name = arg; } private String _name; Change the interface and replace array internally by adding a field for each array element and changing accessors.

37. Refactoring Constants and Variables Replace Array with Object: Mechanics: create a new class for the array change all users of the array to use the class add getters and setters for each element for each element, create a field delete the array compile and test

38. Refactoring Constants and Variables Replace Array with Object: