Refactoring

Refactoring means improving the design of existing code.

Create a new project called flight.

Add two classes to flight: Aeroplane and Helicopter.

Add the following fields and methods to both classes:

double speed;
double altitude;

void takeoff() {
speed = 500;
altitude = 10000;
}

void land() {
speed = 0;
altitude = 0;
}

Extracting a Super Class

We can extract a super class and move selected methods and fields from subclasses to the superclass.

Select:

Refactor>Extract Superclass...

Here's the Extract Superclass dialog:

After this refactoring is performed, Aeroplane and Helicopter are empty subclasses of Aircraft, which contains their fields and methods.

Renaming a Class

We can rename a method, class, or field by selecting:

Refactor>Rename

Use this feature to rename "Aeroplane" "Airplane".

Encapsulate Fields

A quick way to add setters and getters to a selected field is to click:

Refactor>Encapsulate Fields...

Here's the dialog:

Here's the Aircraft code:

public class Aircraft {

private double speed;
private double altitude;

public Aircraft() {
super();
}

void takeoff() {
speed = 500;
setAltitude(10000);
}

void land() {
speed = 0;
setAltitude(0);
}

public void setAltitude(double altitude) {
this.altitude = altitude;
}

public double getAltitude() {
return altitude;
}

public void setSpeed(double speed) {
this.speed = speed;
}

public double getSpeed() {
return speed;
}
}

Pull Up/Push Down

Add the following code the Aircraft:

boolean canHover = false;

void hover() {
if (canHover) {
setSpeed(0);
}
}

Add the following code to Airplane:

void speedUp() {
double amt = 50;
setSpeed(getSpeed() + amt);
}

void slowDown() {
double amt = 50;
setSpeed(getSpeed() - amt);
}

Use pull up and push down to relocate this code.

Converting Local Variables to Fields

Refactor the local variable amt found in speedUp and slowDown to fields.

Converting Fields to Local Variables

Extracting Constants

Use Extract Constant to get rid of the magic numbers in takeoff.