legal identifiers: : identifier « Java Source And Data Type « SCJP

1. SCJP
2. Java Source And Data Type
3. identifier

public class MainClass {
  public static void main(String[] argv) {
    int _a;
    int $c;
    int ______2_w;
    int _$;
    int this_is_a_very_long_identifier;
    int myIdentifier;
    int $my_identifier;
    int $123;
  }
}
/*    
illegal (it's your job to recognize why):

int :b;
int -d;
int e#;
int .f;
int 7g;


*/