How to create an Apex class

Preface – This post is part of the Object Oriented Thinking series.

Enough theoretical talk about what classes are – it’s time to get our hands dirty and code one!

First things first, here’s where you go in your org to create a class:
Setup >> Develop >> Apex Classes >> New

For this tutorial, let’s build our X-wing class!

If you don’t know what an X-Wing is, you have homework to do!

Every class has three components to it: [1] Attributes, [2] Methods, and [3] Constructors.

1. Attributes

Attributes are the variables that describe your class. Your class’s attributes can be any data type, collection, or even class! Think of attributes to be just like custom fields, except they exist on your class instead of a Salesforce object.

// Basic data type attributes
String  name;
Integer protonTorpedoes;
Integer deathStarsDestroyed;
Decimal powerRemaining;
// Attributes related to Salesforce objects - like lookups!
User    pilot;
Account manufacturer;
// Attributes related to other classes - also like lookups!
LaserCannon      lasers;
HyperdriveEngine engine;
DeflectorShield  shield;
AstromechDroid   droid;

Note that the LaserCannon, HyperdriveEngine, and DeflectorShield classes referenced above would have to already exist for this class to save!

2. Methods

Methods are the actions available to objects of your class. You define the logic inside each method, what inputs are required (if any), and what value is returned (if any). Here’s the general template:

public ReturnType MethodName(Input1Type Input1Variable) {
  // Method logic goes here!
}

ReturnType is simply the data type, collection, or class that’s returned when your method is called. For example, if your method took two Integers and added them together, your return type would be Integer. If you don’t want your method to return anything, use void.

MethodName is whatever you want to name your method! Make sure to choose a method name so descriptive that a Wookiee could understand it! Also, don’t forget to use camelCase.

Input1Type is the data type, collection, or class that represents your first accepted input, and Input1Variable is the variable name you’re assigning it to so you can reference it in your method’s logic. You can add more inputs to your method by separating them with commas.

Let’s create a few methods for our class:

// This method has one input and doesn't return anything
public void shootLasers(Integer numberOfShots) {
  for (Integer i = 0; i < numberOfShots; i++) {
    System.debug('PEW!');
  }
}

// Notice how this method references class attributes!
public void fireProtonTorpedo() {
  if (protonTorpedoes > 0) {
    System.debug('Shoop... KABOOM!!!');
    protonTorpedoes--;      // This decrements the variable by 1
    deathStarsDestroyed++;  // This increments the variable by 1
  }
} 

// This method returns a value!
public Boolean initiateHyperdrive() {
  Boolean isSuccess = false;    
  if (powerRemaining > 0.10) {
    System.debug('Zoom zoom, WEEE!');
    powerRemaining = powerRemaining - 0.10;
    isSuccess = true;
  }
  return isSuccess;
}

3. Constructors

Constructors are the methods that create new instances of your class, aka objects. Just like with methods, you define the logic and what inputs are required (if any). The difference with methods is that you don’t define a return type because constructors always return a new object.

The goal of a constructor is to prepare your new object for use!

// The name of the constructor "method" is always the class name
public XWing(String nickname, User myUser) {
  name                = nickname;  
  protonTorpedoes     = 2;
  deathStarsDestroyed = 0;
  powerRemaining      = 1.00;
  pilot               = myUser;
}

Constructors are totally optional – Apex automatically creates a default constructor that simply creates a new object with all empty attributes.

Putting it all together…

public class XWing {
  // Attributes usually come first!
  String  name;
  Integer protonTorpedoes;
  Integer deathStarsDestroyed;
  Decimal powerRemaining;
  User    pilot;
  Account manufacturer;
  LaserCannon      lasers;
  HyperdriveEngine engine;
  DeflectorShield  shield;
  AstromechDroid   droid;
  // Constructor(s) are next
  public XWing(String nickname, User myUser) {
    name                = nickname;  
    protonTorpedoes     = 2;
    deathStarsDestroyed = 0;
    powerRemaining      = 1.00;
    pilot               = myUser;
  }

  // Finally comes the methods
  public void shootLasers(Integer numberOfShots) {
    for (Integer i = 0; i < numberOfShots; i++) {
      System.debug('PEW!');
    }
  }

  public void fireProtonTorpedo() {
    if (protonTorpedoes > 0) {
      System.debug('KABOOM!!!');
      protonTorpedoes--;  
      deathStarsDestroyed++;
    }
  } 

  public Boolean initiateHyperdrive() {
    Boolean isSuccess = false;    
    if (powerRemaining > 0.10) {
      System.debug('Zoom zoom, WEEE!');
      powerRemaining = powerRemaining - 0.10;
      isSuccess = true;
    }
    return isSuccess;
  }
}

We’re now ready to start creating objects of this class in our code!

Starting to wrap your head around the concept of objects and classes? Don’t worry if it’s still a little fuzzy to you, it takes months of practice for most people to understand these concepts.

We’ll put this class to you in the next post to “force” it in your head!

Next post: How to use objects in your code!