It seems that is imposible to type the ˜ symbol (named also tilde,squiggle,twiddle,not,approx,wiggle,swung,dash,enyay,sqiggle) in Netbeans with a Swedish keyboard at least. It seems that it’s a long known java bug (bug 6353098, bug 6253172). At least I can use the Alt+126 code to type it.