In OS X Lion and later Apple has introduced a feature where holding down a key brings up a popup menu with a choice of accented characters. Here is brief Apple release note on this feature:

Press-and-Hold for Certain Keys

A new system-wide behavior has been implemented for cases in which the user presses and holds down certain keys while editing text. Instead of repeating the key, this new behavior provides a mechanism for entering alternative (usually accented) forms. UI appears near the text showing these alternative forms, which can be selected by clicking, by arrowing, or by pressing a digit corresponding to the index of the desired form. Keys other than letter and digit keys continue to repeat when pressed and held.

This new behavior generally should be active only in cases in which text is actually being edited, but there are a few cases in which it may need to be turned off explicitly. There is a default provided for this, ApplePressAndHoldEnabled, which may be set to NO to turn off the new press-and-hold behavior and re-enable key repeat for all keys. This may be set for a specific application, to control the behavior for that application only, or globally, to control the behavior for all applications.


The "ApplePressAndHoldEnabled" boolean preference can be set per application, but it appears Netbeans currenlty does not respect this option at all. 

Issuing

defaults write org.netbeans.ide.baseide.201302132200 ApplePressAndHoldEnabled -bool false

command from Terminal has no effect. This only creates 

~/Library/Preferences/org.netbeans.ide.baseide.201302132200.plist

file with that setting set to false, but Netbeans does not read the file on startup. 

In Defect 206589 (closed as resolved) it was recommended users turn off this feature globally (with defaults write -g ApplePressAndHoldEnabled -bool false ), but this is not generally acceptable, since some users who often type diacritical characters depend on this system feature.

The proper solution would be for Netbeans to have a preference file in 

~/Library/Preferences/org.netbeans.ide.plist 

(or whatever the netbeans bundle ID is) which it should then read on startup and change its behaviour based on settings specified in the file. The added benefit of this solution is that OS X defaults command can now also set the Netbeans settings.