JLS100708：Note on JLS, Ch1~Ch3

 

@ http://zcatt.cublog.cn

 

Hist:

100708, draft

 

 

 

Chapter1 Intorduction

The Java language is a general-purpose, concurrent, class-based, OO languages.

The Java language is strongly typed. It is a relatively high-level language and normally compiled to the bytecoded instruction set and bin format.

JLS does not describe reflection. Readers should be aware of this.

 

Chapter 2 Grammars

Context-Free Grammars:  production, nonterminal, terminal, left-hand, and right-hand. Language and sentence.

The Lexical Grammar: token, identifier, keyword, literal, separator, operator

Syntactic Grammar.

 

Chapter 3 Lexical Structure

Unicode

Java are writteng using the Unicode character set. The range of legal code points is now U+0000 to U+10FFFF. Characters whose code points are greater than U+FFFF are called supplementary characters. Unicode standard defines an encoding called UTF-16, which use paires of 16-bit code units to represent supplementary characters. For characters in the range U+0000 to U+FFFF, the values of code points and UTF-16 code units are the same. Tha Java represents text in sequences of 16-bit code untis, using the UTF-16 encoding.

 

Lexical Translations

3 steps: 1) translate the Unicode escaps ‘\uxxxx’ in raw stream of Unicode characters to the corresponding Unicode character. 2)translate into a stream of input characters and line terminators. 3)comprise the tokens that are the terminals symbols of the syntactic grammar, after discarding ws and comments.

 

Unicode Escapes

\u followed by four hex digits with the indicated hex value. The character produced by a Unicode escape does not participate in further Unicode escapes.

The Java language specifies a standard way of transforming a program written in Unicode into ASCII that changes a program into a form that can be processed by ASCII-based tools.

 

Line Terminators

LF, CR, or CR LF

 

 

Input Elements and Tokens

 

WS

SP, HT, FF, or LineTerminator

 

Comments

/* traditional comment */

// end-of-line comment

Comments do not nest.

/*, */, and // have no special meaning in comments.

 

 

Identifiers

 

Keyword

One of :

abstract continue for new switch

assert default if package synchronized

boolean do goto private this

break double implements protected throw

byte else import public throws

case enum instanceof return transient

catch extends int short try

char final interface static void

class finally long strictfp volatile

const float native super while

Attention: true , false, and null are not here.

 

Literals

A literal is the source code representation of a value of a primitive type, the String type, or the null type.

 

Integer literals: decimal, hexadecimal, or octal.

Decimal:  0,  123, 1234566666666666L

Hexadecimal:  0x12ab, 0x7fffffffffffffffffffL

Octal: 017777, 077777777777777L

 

Float literals

 

Boolean literals

true, or false

 

Character literals

A character or an escape sequence: \uxxxx

 

String literals

Zero or more characters enclosed in double quotes. Each string literal is a reference to an instance of class String. String objects have a constant value.  

 

Escape Sequences for characters and String literals

\b BS, \u0008

\t HT, \u0009

\n LF, \u000a

\f FF, \u000c

\r CR, \u000d

\” double quote, \u0022

\’ single quote, \u0027

\\ backslash, u\005c

octalEscape, such as \777, from \u0000 to \u00ff

 

 

The Null literal

Null

 

Separators

( ) { } [ ] ; , .

 

Operators

= > < ! ~ ? :

== <= >= != && || ++ --

+ - * / & | ^ % << >> >>>

+= -= *= /= &= |= ^= %= <<= >>= >>>=

 

 

REF

1.       JLS 3nd

2.       JVM 2nd