1. Small changes to code to improve it
Refactoring
Small changes to code to improve it

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

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

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

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

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

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++;

8. 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?

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;

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; }

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