Best Practices for Initializing Variables in Constructors

constructorsvariables

I try to use the best coding standards/practices, however in all of my googling and classes I have never learned which is proper form for declaring/defining variables like the examples below. I have seen numerous different people (teachers, classmates, coworkers) define variables inside and outside of the constructor seemingly at random. Any information about this would be awesome!

class Foo
{
    private static int firstNumber = 1;
    private int secondNumber = 25;
    private FooBar fooBar = new FooBar();

    public Foo()
    {
    }
}

class Foo
{
    private static int firstNumber;
    private int secondNumber;
    private FooBar fooBar;

    public Foo()
    {
        firstNumber = 1;
        secondNumber = 25;
        fooBar = new FooBar();
    }
}

Best Answer

Given that you have declared some of the variables "static", use the first option.

Static variables are not bound to one instance of a class - they are shared across all of them. They even exist before you have created an instance.

The second initialises them in the constructor, which means their values are not set to the desired values until you call the constructor. Every time you call the constructor, it initialises them again.

The first option is simpler and behaves as expected.

Related Solutions

Java – Declaring Variables Inside or Outside a Loop

The common answer to most of these questions should be "why don't you try it and find out?". In Java you could probably take a look at the generated bytecode (I believe the tool is called javap), to see what the difference in byte code is between those two ways of declaring the variable.

Doing it like that is a better learning experience for you, because next time you're running into an optimization issue you can use the same tool to verify that the compiler is doing what you are expecting - it will help you avoid needlessly changing your coding style when the optimizer does fine on its own, or finding actual tweaks when you really need that last bit of performance.

Design Patterns – Patterns for Subclass Constructors Varying Parent Class Constructor

The abstract Controller class can't create the right <concrete class>Domain classes, because it doesn't know which concrete class it belongs to and which Domain and View classes it should be associated with.

What you can do is pass in the Domain and View classes from the derived class's constructor.

abstract class Controller
{
  private $domain;
  private $view;

  function __construct($aDomain, $aView) {
    $this->domain = $aDomain;
    $this->view = $aView;
  }
}

class BlogPageController extends Controller
{
  function __construct() {
    parent::__construct(new BlogPageDomain, new BlogPageView);
  }
}

Best Answer

Related Solutions

Java – Declaring Variables Inside or Outside a Loop

Design Patterns – Patterns for Subclass Constructors Varying Parent Class Constructor

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