You should be testing this sort of thing rather than asking about it.
String one = 'Hello World ! ";
String two = 'Hello World ! ";
OR
String one = 'Hello World ! ";
String two = new String ('Hello World ! ") ;
Apart from the fact that your code will only compile if you change the ' to ", you will see for yourself. You learn so much more by trying out code for yourself. Even apparently trivial little bits of code which run in three lines teach you something.