identifiers

■ Java identifiers can only begin with three things:

a letter (A-Z or a-z)

a dollar sign ($)

an underscore ( _ )

No digits or punctuations.

■ Identifiers can contain the aforementioned three things plus digits (0-9) inside their bodies or at the end. Anything else is illegal. i.e.

double d_1; and

float f$; will both compile.

int no.1 = 1; and

String @address; will not compile

■ You cannot use a reserved word as an identifier. i.e.

double do = 2;

float for = 1;

byte switch = 0; None of these three statements will compile.