What is lazy loading?

public class Example {
private Vector data = null;
public Vector getData() {
if (this.data == null) {
this.data = new Vector();
// Load data into vector …
}
return this.data;
}
}

This technique is most useful when you have large hierarchies of objects (such as a product catalog). You can lazy-load subordinate objects as you navigate down the hierarchy, and thereby only create objects when you need them.

The term lazy loading is usually used when talking about object relational mappers. If you use ADO.NET directly you always get eager loading (ie it always loads just what you specify).

OR-mappers like nHibernate support returning proxy objects that get "filled in" with the right data only when you access the data. That way you only load the data that you really use. This is a usefull feature when you specify a lot of relations between objects that can get loaded from the database, you don't want the OR-mapper to load all the related objects and the objects related to the related objects and so on. That can result in your whole database getting loaded.

This problem can be prevented by carefull design of your object model too. (using aggregates and only loading aggregate roots like in domain driven design is a way to get around this without using lazy loading).

We can have this in Java,.Net

Read the follwoing links to get a clear overview

http://msdn.microsoft.com/en-us/library/vstudio/dd456846(v=vs.100).aspx

http://www.digital-web.com/articles/improve_page_performance_with_lazy_loading/

http://whatis.techtarget.com/definition/lazy-loading-dynamic-function-loading

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