You can only re-use an existing character. e.g. \0
If you put this in a String, you will have a String with one character in it.
Say you want a char
such that when you do
String s =
char ch = ?
String s2 = s + ch; // there is not char which does this.
assert s.equals(s2);
what you have to do instead is
String s =
char ch = MY_NULL_CHAR;
String s2 = ch == MY_NULL_CHAR ? s : s + ch;
assert s.equals(s2);