Normalization in DOM parsing with java - how does it work?

Question

I saw the line below in code for a DOM parser at this tutorial.

doc.getDocumentElement().normalize(); 

Why do we do this normalization ?
I read the docs but I could not understand a word.

Puts all Text nodes in the full depth of the sub-tree underneath this Node

Okay, then can someone show me (preferably with a picture) what this tree looks like ?

Can anyone explain me why normalization is needed?
What happens if we don't normalize ?

Answer 1

The rest of the sentence is:

where only structure (e.g., elements, comments, processing instructions, CDATA sections, and entity references) separates Text nodes, i.e., there are neither adjacent Text nodes nor empty Text nodes.

This basically means that the following XML element

<foo>hello  wor ld</foo> 

could be represented like this in a denormalized node:

Element foo     Text node: ""     Text node: "Hello "     Text node: "wor"     Text node: "ld" 

When normalized, the node will look like this

Element foo     Text node: "Hello world" 

And the same goes for attributes: <foo bar="Hello world"/>, comments, etc.

Answer 2

In simple, Normalisation is Reduction of Redundancies.
Examples of Redundancies:
a) white spaces outside of the root/document tags(...<document></document>...)
b) white spaces within start tag (<...>) and end tag (</...>)
c) white spaces between attributes and their values (ie. spaces between key name and =")
d) superfluous namespace declarations
e) line breaks/white spaces in texts of attributes and tags
f) comments etc...