Small changes to code to improve it

Transcription

1 Small changes to code to improve it 1

2 Refactoring Defined A change made to the internal structure of software to make it easier to understand and cheaper to modify without changing its observable behavior Refactoring, Martin Fowler. et. al., page 53 Martin wrote the book: Refactoring Improving the Design of Existing Code Refactoring owes a lot to a Refactoring: William Opdyke's PhD thesis 2

3 Write Drafts and Revise All good writing is based upon revision. Jacques Barzun, Simple & Direct, 4th Edition Revision means "to look at again" Example: Before 4-July, 1776, Thomas Jefferson's draft of the Declaration of Independence had this "We hold these truths to be sacred and undeniable,..." He let his friend Benjamin Franklin look over this draft to make changes including this: "We hold these truths to be self-evident,..." Total of 47 revisions, then Congress made 39 more 3

4 Refactoring Happens In larger systems (frameworks), code will be read and modified more frequently than it will be written Refactoring typically involves Removing duplicated or dead code Simplifying complex code Clarifying unclear code It turns out that removing code can actually be a good thing: your system has fewer lines of code Easier to develop, maintain, and change Refactoring can be risky, unless you do it in small steps and have automated tests that can be run anytime 4

5 A few examples A few refactorings we've seen (they have names) Encapsulate Field (do this virtually always) add getters and/or setters to access a field Rename Method (often) Extract SuperClass (recall Shape and Fruit) You have two classes with similar features Create a superclass and move common features to the superclass Compose Method A variety of refactorings can happen at the method level 5

6 Composed Method Some refactoring attempts to "compose" methods A composed method is relatively short by using calls to a small number of coherent elements Easier to understand what the method does Some refactorings for composing methods Extract Method: replace complex code with a nice name Inline Method: use code that's as easy to read as method Code demo: Compose insertelement in ArrayPriorityList 6

7 Before public void insertelementat(int index, E el) { // If need to grow array, grow it if (size() == data.length) { Object[] temp = new Object[data.length + 20]; for (int i = 0; i < size; i++) temp[i] = data[i]; data = temp; // Shift array elements right to make room for (int j = size; j > index; j--) { data[j] = data[j - 1]; // Add new element at the provided index data[index] = el; size++; 7

8 After public void insertelementat(int index, E el) { if (shouldgrowarray()) gowarray(); makeroomat(index); addat(index, el); Is the new insertelementat more readable? Vote: Yes: Nay: Are the extra private methods in the way? Vote: Yes: Nay: 8

9 private void addat(int index, E el) { data[index] = el; size++; private void makeroomat(int index) { for (int j = size; j > index; j--) { data[j] = data[j - 1]; private void gowarray() { Object[] temp = new Object[data.length + 20]; for (int i = 0; i < size; i++) temp[i] = data[i]; data = temp; 9

10 Replace Nested Conditional with Guard Clauses see link private int bogglescoreof(string word) { int sum = 0; if (next.length() == 3 next.length() == 4) sum = 1; else if (next.length() == 5) sum = 2; else if (next.length() == 6) sum = 3; else if (next.length() == 7) sum = 5; else if (next.length() >= 8) sum = 11; else sum = 0; return sum; 10

11 Refactoring Catalog Buy the book or check out Martin's Refactoring Catalog from the refactoring page Find catalog link and then find and read Inline Method Before test 2 read all 27 Refactorings on the next slide to prepare for the test 2 on Thursday 18-Nov 11

12 Some of these will be on test 1. Add Parameter 2. Collapse Hierarchy 3. Consolidate Conditional Expression 4. Consolidate Duplicate Conditional Fragments 5. Decompose Conditional 6. Encapsulate Collection Read the following refactorings Polymorphism from (liste 19. Replace Iteration with Recursion d here in alphabetic order) 7. Encapsulate Field 8. Extract Class 9. Extract Method Modifier 10. Extract Superclass 11. Hide Method 12. Inline Method 13. Parameterize Method Pull up Field 14. Pull Up Method 15. Remove Double Negative 16. Replace Assignment with Initialization 17. Replace Conditional with 18. Replace Inheritance with Delegation 20.Remove Control Flag 21. Replace Error Code with Exception 22. Replace Exception with Test 23. Replace Magic Number with Symbolic Constant 24. Replace Nested Conditional with Guard Clauses 25. Replace Recursion with Iteration 26.Reverse Conditional 27. Separate Query from Modifier 12

13 A dozen questions like this g) Which design is better, I or II? Why? I void printowing() { printbanner(); // print details System.out.println("name: System.out.println("amount II void printowing() { printbanner(); printdetails(getoutstanding()); " + _name); " + getoutstanding()); void printdetails (double outstanding) { System.out.println ("name: " + _name); System.out.println ("amount " + outstanding); 13

14 Answer g) II Why? If you have a code fragment that can be grouped together, use Extract Method to turn the fragment into a method whose name explains the purpose of the method 14