<p>How can I turn off the wavy red underlines in Netbeans? I don't want to be interrupted while I'm typing, and told that a half finished line of code is wrong.</p>

Follow this path if you want to turn them off, (I'm using NeatBeans 5.5.1)
Tools ->
Options ->
Advanced Options ->
Open the "Editing" node and click on "Java sources" ->
Enter 0 for the "Error Annotation Limit"
That will completely turn off the red underlines. You can also change the "automatic parsing delay" at the same location if you want a longer pause instead.