CPSC 210

D3: Refactoring

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Learning Goals

To improve the design of an existing code base through refactoring
To improve coupling by abstracting duplicated code into methods
To improve cohesion by splitting up classes

Cohesion (SRP): High = Good

Coupling: Low = Good

Refactoring

Improving code structure without changing functionality

Fully working code base with tests!

Tests keep passing!

Refactoring (2)

When we refactor code...
- we do not change the functionality of the code
- we want to improve the structure of the code
We want to improve code structure by...
- reducing repetitive code
- reducing coupling
- increasing cohesion (SRP)

Real-World Example

...from a tool that you all know and love...

https://github.com/checkstyle/checkstyle/pull/6899#pullrequestreview-261657898
https://github.com/checkstyle/checkstyle/pull/6905

Lecture Ticket

Duplication between the two methods!
We want to refactor and extract a helper method

What lines to pull out from each method?
What to pass into the method when called from each method?
What is the return type of the helper method?

public class LittleClass {

  public int doThingOne() {
    int numTimes = 6;
    int multiplier = 5;
    numTimes += 1;
    for (int i = 0; i < numTimes; i++) {
      System.out.println(multiplier * i);
    }
    return numTimes;
  }

  public void doThingTwo() {
    int occurrences = 3;
    int timeser = 10;
    System.out.println("Doing thing two");
    for (int i = 0; i < occurrences; i++) {
      System.out.println(timeser * i);
    }
    System.out.println("Doing thing two");
  }

}