Naming restrictions of variables in java

Question

Why are special characters (except $, _) not allowed in Java variable names?

Answer 1

The following code is all valid in Java...

int Δ = 1;
double π = 3.141592;
String 你好 = "hello";
Δ++;
System.out.println(Δ);

I'd say those are pretty special characters for variable names.

Source : http://rosettacode.org/wiki/Unicode_variable_names#Java