Wednesday, February 11, 2004


I was looking for more information about this today and found this (Martin Fowler has an eariler article and so does Michael Yuan):
"The best way to describe what IoC is about, and what benefits it can provide, is to look at a simple example. The following JDBCDataManger class is used to manage our application's accessing of the database. This application is currently using raw JDBC for persistence. To access the persistence store via JDBC, the JDBCDataManger will need a DataSource object. The standard approach would be to hard code this DataSource object into the class, like this:

public class JDBCDataManger {
public void accessData() {
DataSource dataSource = new DataSource();
//access data

Given that JDBCDataManger is handling all data access for our application, hard coding the DataSource isn't that bad, but we may want to further abstract the DataSource, perhaps getting it via some system-wide property object:

public class JDBCDataManger {
public void accessData() {
DataSource dataSource =

In either case, the JDBCDataManger has to fetch the DataSource itself.

IoC takes a different approach — with IoC, the JDBCDataManger would declare its need for a DataSource and have one provided to it by an IoC framework. This means that the component would no longer need to know how to get the dependency, resulting in cleaner, more focused, and more flexible code."

A Brief Introduction to IoC
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