Q:

How to show/reveal hidden or invisible characters in NetBeans?

How can you show/reveal hidden characters in NetBeans?  In other editors, if this feature is turned on, a space might be shown as a small centered dot, and a tab as a right arrow.  (This feature is useful to see if a file uses tabs or spaces for indentation, among other things.)

A:

This feature was missing for a long time—a feature request was created on November 1999 and it was finally implemented on August 2010 (NetBeans 6.10). You can enable/disable it at "View → Show Non-printable Characters".
Bug history
As of NetBeans 7.0.1, the definition for "non-printable" seems to include tabs and carriage returns but not regular white space char:

NetBeans 7.1.0 finally displays spaces. However, now it has a new bug where consecutive tabs (or tabs & spaces combinations) collapse into one tab:

NetBeans 7.4.0 fixes this:

There're yet a couple of issues:

The end of file is represented with the same symbol as line feeds, thus making it non-obvious to determine whether the file ends with EOL.
Hidden chars are displayed in the same colour as regular text.

These issues have not been addressed so far but they can be sort of mitigated with the Editor Whitespace third-party plugin, which:

Hides the EOL and EOF markers (which aren't useful anyway).
Displays other whitespace characters using always the same colour.

A:

in netbeans 7 you can enable display of spaces, tabs & line feeds like this:
spaces

download font from: http://netbeans.org/bugzilla/attachment.cgi?id=97902
install the ttf font
tools > options > font & colors > Syntax > All Languages > Whitespaces
choose the installed whitespace font
more info about the netbeans 6 bug: http://netbeans.org/bugzilla/show_bug.cgi?id=4619

tabs & line feeds
in netbeans 7 you can enable to see non-printable characters:

view > show non-printable characters

in netbeans 6 only the spaces part works

A:

Using Netbeans 8.0.1
View-> Show Non-Printable characters

