I have a string
May 1988 – June 1992
String sample="May 1988 – June 1992";
String arr=sample.split(" - ");
The String you are trying to split has a "en dash" (U+2013), while you try to split with a "HYPHEN-MINUS" (U+002D). Seeing the difference with your eyes is pretty hard (dash is slighly longer), but they are different symbols.
just copy and paste the en dash into your split method and it should work:
String arr=sample.split(" – ");