Inversion of Control

Inversion of Control (IoC)

Hollywood Principle:

Don’t call us, we’ll call you.

Framework v.s. Library

One important characteristic of a framework is that the methods defined by the user to tailor the framework will often be called from within the framework itself, rather than from the user’s application code. The framework often plays the role of the main program in coordinating and sequencing application activity. This inversion of control gives frameworks the power to serve as extensible skeletons. The methods supplied by the user tailor the generic algorithms defined in the framework for a particular application.

– Ralph Johnson and Brian Foote

Example

JUnit Framework setUp and tearDown

Lightweight containers

J2EE

Dependency Injection

• Constructor Injection
• Setter Injection
• Interface Injection

    private MutablePicoContainer configureContainer() {
        MutablePicoContainer pico = new DefaultPicoContainer();
        Parameter[] finderParams =  {new ConstantParameter("movies1.txt")};
        pico.registerComponentImplementation(MovieFinder.class, ColonMovieFinder.class, finderParams);
        pico.registerComponentImplementation(MovieLister.class);
        return pico;
    }

PicoContainer NanoContainer: XML configure mapping

PicoContainer

Spring

Avalon

Interface Injection

References

1. Inversion of Control Containers and the Dependency Injection pattern, Martin Fowler