2

C H A P T E R

Grammars

Grammar, which knows how to control even kings . . .

Moliere

, Les Femmes Savantes

(1672), Act II, scene vi

T

HIS chapter describes the context free grammars used in this specification to

define the lexical and syntactic structure of a Java program.

2.1   Context Free Grammars

A

context free grammar

 consists of a number of

productions

. Each production has

an abstract symbol called a

nonterminal

 as its

left hand side

, and a sequence of

one or more nonterminal and

terminal

 symbols as its

right hand side

. For each

grammar, the terminal symbols are drawn from a specified

alphabet

.

Starting from a sentence consisting of a single distinguished nonterminal,

called the

goal symbol

, a given context free grammar specifies a

language

,

namely, the infinite set of possible sequences of terminal symbols that can result

from repeatedly replacing any nonterminal in the sequence with a right hand side

of a production for which the nonterminal is the left hand side.

2.2   The Lexical Grammar

A

lexical grammar

 for Java is given in  3. This grammar has as its terminal sym 

bols the characters of the Unicode character set. It defines a set of productions,

starting from the goal symbol

Input

( 3.5), that describe how sequences of Uni 

code characters ( 3.1) are translated into a sequence of input elements ( 3.5).

These input elements, with white space ( 3.6) and comments ( 3.7) dis 

carded, form the terminal symbols for the syntactic grammar for Java and are

called Java

tokens

 ( 3.5). These tokens are the identifiers ( 3.8), keywords ( 3.9),

literals ( 3.10), separators ( 3.11), and operators ( 3.11) of the Java language.

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