Refactoring 001 - Remove Setters
Maximiliano Contieri
Engineering Manager@Avature | CS Teacher@UBA | Book Author@O'Reilly | MaximilianoContieri.com
Setters violate immutability and add accidental coupling
TL;DR: Make your attributes private to favor mutability
Problems Addressed
Related Code Smells
Steps
Sample Code
Before
public class Point {
protected int x;
protected int y;
public Point() {
this.x = 0;
this.y = 0;
}
public void setX(int x) {
this.x = x;
}
public void setY(int y) {
this.y = y;
}
}
Point location = new Point();
// At this moment, it is not clear which points represent
// It is coupled to the constructor decision.
// Might be null or some other convention
location.setX(1);
// Now you have point(1,0)
location.setY(2);
// Now you have point(1,2)
public class Car {
protected int speed;
public Car() {
}
public void setSpeed(Speed desiredSpeed) {
this.speed = desiredSpeed;
}
}
Car tesla = new Car();
// We have no speed??
tesla.setSpeed(100 km/h);
// Now our car runs fast
After
// 1. Locate setters usage
location.setX(1);
location.setY(2);
// 2. If you are setting essential properties move
// them to the constructor and remove the method
public class Point {
public Point(int x, int y) {
this.x = x;
this.y = y;
// We remove the setters
}
Point location = new Point(1, 2);
public class Car {
protected int speed;
public Car() {
this.speed = 0 km/h;
}
public void speed(Speed desiredSpeed) {
this.speed = desiredSpeed;
}
}
// 1. Locate the setters usage
// 3. If you need to change an accidental property
// it is not a setter. Remove the setXXX prefix
Car tesla = new Car();
// Our car is stopped
tesla.speed(100 km/h);
// We tell the desired speed. We don't set anything
// We don't care if the car stores its new speed.
// if it manages through the engine
// if the road is moving etc
Type
[X] Semi-Automatic
We should detect setters (unless they use meta-programming) with our IDEs.
We can also remove them and see which tests fail if we have good coverage.
Safety
This is not a safe refactoring since you might miss some methods calling the removed setters.
You need to make sure to have good coverage and also an excellent QA process to ensure a smooth refactoring.
Why is the Code Better?
This refactoring improves encapsulation and integrity adding an extra access control layer.
Refactor with AI
Without Proper Instructions
With Specific Instructions
Tags
Related Refactorings
Remove Getters
Credits
This article is part of the Refactoring Series