Inversion of Control is a principle which recommends moving unwanted responsibilities out of a class and letting the class focus on core responsibilities, hence providing loose coupling.

There are two basic ways in Java to provide IOC- Dependency Injection and Dependency lookup.

As the name suggest, Dependency Injection is where the dependency is injected from outside the class, and class is not worried about details – http://kamalmeet.com/coding/more-on-dependency-injection/

Dependency lookup is where class itself looks up for dependency and chooses appropriate implementation. Use of JNDI lookup for proper bean of datasource is a good example.

InitialContext ic = new InitialContext();
DataSource ds = (DataSource) ic.lookup(“jndiName”);