This hint catches:
String test = "blah";
StringBuilder builder = new StringBuilder();
builder.append("blah"+test);

but does not catch:
String test = "blah";
StringBuilder builder = new StringBuilder();
builder.append("blah"+"blah");



If you have code that has:

String blarg = 
"blah blah blah" +
" blah blah blah" +
" blah blah blah" +
" blah blah blah" +;

it would be nice if netbeans could auto-convert that to:

StringBuilder builder = new StringBuilder();
builder.append("blah blah blah");
builder.append(" blah blah blah");
builder.append(" blah blah blah");
builder.append(" blah blah blah");
String blarg = builder.toString();

Or convert to chained .append would work, but not as cleanly in my opinion.  

I would guess that the java compiler converts the concatenation of string literals into one big string in bytecode, but when you have a giant string like that and you're working to refactor the code around it, it would be nice if netbeans had an auto-convert to StringBuilder.