Avoid your getters and setters, Part 1

In the Java world, getters and setters are one of those things everyone says to hate but everyone actually uses.
I think this is mainly because:

1. They are procedural, heritage of C-style (or even older) programming.


2. They are a practice embedded by JavaBeans conventions.


3. Many ORM and Web frameworks heavily use getters and setters.

In a series of blog posts called Avoid your getters and setters, I'll try to show you some ideas for avoiding getters and setters, by simply applying some fundamental Object Oriented and Domain Driven Design principles.

Any feedback will be highly appreciated.

Let's go!

Avoid your getters and setters: Programming to an Interface

From the GOF book:

Don't declare variables to be instances of particular concrete classes. Instead, commit only to an interface
defined by an abstract class.

This is probably the main Object Oriented principle: we could write words and words about it, but I prefer to remind you some good books like the one cited above, or like this one.

Programming to an interface is the first step toward good OO code.
Moreover, and here we come to our point, if you program to an interface, and think in terms of interfaces, you can better choose the getters and setters you need, while removing or hiding the unwanted ones.

First, thinking in terms of interfaces is thinking in terms of contracts.
Say you have a Customer entity in your domain model.
How does it interact with other entities?
What are its behaviours?
What its pre / post conditions and invariants?
That is: what is the contract defined by the Customer interface?

You may have an issue(Order ) method, and you may discover you need to know, for business reasons, the customer code.
So, here is our Customer interface:

public interface Customer {
  
  public String getCustomerCode();

  public void issue(Order newOrder);
}

Think always in terms of business contracts: all methods in your interfaces must have a business meaning.
Obviously, also getters and setters can have business meaning, which is the case of getCustomerCode().
All getters and setters without this meaning must be removed from the interface.

Here it comes your preferred ORM tool or Web Framework: it requires a lot of setters and getters for writing and reading properties, and you really don't want to do all that dirty job by hand!

What to do?

Too bad, we cannot actually avoid all those getters and setters, but we can hide them from your code simply declaring them in your concrete classes, and leaving them out from interfaces: your code, depending on interfaces, will never see all those unwanted methods!.

So you have a Customer concrete class:

public class CustomerImpl implements Customer{
  
  ...

  public String getCustomerCode() { ... }

  public void issue(Order newOrder) { ... }

  // Setters and getters not in the interface:

  public void setSurname(String surname) { ... }

  public String getSurname() { ... }
}

What really hurts is the setSurname() method: in your business, once defined a customer's surname should never change!
But, hey: your code is written in terms of the Customer interface, so it will not be able to call unwanted methods!

public class CustomerService {
  
  public void register(Customer c) { ... }
}


public class CustomerDAO {
  
  public void save(Customer c) { ... }
}

Moreover, under the hood they actually are CustomerImpl objects, so your Web or ORM frameworks will be able to call all getters and setters thanks to Java reflection!



That's all.
And it's awful simple.
I hope to have explained well how you can hide getters and setters by simply programming to interfaces, while still using common frameworks.

In my next Avoid your getters and setters post we'll talk about the expert pattern ... in the meantime, let me know what do you think!