Small changes to code to improve it Refactoring Small changes to code to improve it

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

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 http://www.weeklyreader.com/googledocs/pdfs/revisionfiles.pdf

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

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

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

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++;

After Is the new insertElementAt more readable? 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?

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;

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; }

Refactoring Catalog http://www.refactoring.com/catalog/ Check out Martin's Refactoring Catalog from the refactoring page http://www.refactoring.com/catalog/