Lexical Structure (JDK8-jsl)

java jsl study

Unicode

• Unicode 6.2

• Everything is writen in unicode

  Unicode Escapes

  UnicodeInputCharacter:
    UnicodeEscape
    RawInputCharacter
  UnicodeEscape:
    \ UnicodeMarker HexDigit HexDigit HexDigit HexDigit
  UnicodeMarker:
    u {u}
  HexDigit:
    (one of)
    0 1 2 3 4 5 6 7 8 9 a b c d e f A B C D E F
  RawInputCharacter:
    any Unicode character

  Special Chars

• Line Terminators : LF,CR,LFCR
• White Spaces : SP,HT.FF
• Comments : /../ , //

Identifiers

Identifier:
    IdentifierChars but not a Keyword or BooleanLiteral or NullLiteral
IdentifierChars:
    JavaLetter {JavaLetterOrDigit}
JavaLetter:
    any Unicode character that is a "Java letter"
JavaLetterOrDigit:
    any Unicode character that is a "Java letter-or-digit"

• Two identifiers are the same only if they are identical, that is, have the same Unicode character for each letter or digit. Identifiers that have the same external appearance may yet be different.
• The "Java letters" include uppercase and lowercase ASCII Latin letters A-Z (\u0041-\u005a), and a-z (\u0061-\u007a), and, for historical reasons, the ASCII underscore (_, or \u005f) and dollar sign ($, or \u0024). The $ sign should be used only in mechanically generated source code or, rarely, to access pre-existing names on legacy systems.

Keywords, Boolean Literals, Null Literals

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

• 50, can not be used as identifiers
• treu/false
• null
• after jdk9, underscore cannot be used as identifiers

Integer

IntegerLiteral:
    DecimalIntegerLiteral
    HexIntegerLiteral
    OctalIntegerLiteral
    BinaryIntegerLiteral
DecimalIntegerLiteral:
    DecimalNumeral [IntegerTypeSuffix]
HexIntegerLiteral:
    HexNumeral [IntegerTypeSuffix]
OctalIntegerLiteral:
    OctalNumeral [IntegerTypeSuffix]
BinaryIntegerLiteral:
    BinaryNumeral [IntegerTypeSuffix]
IntegerTypeSuffix:
    (one of)
    l L

• Suffix : L for type long
• Decimal : 0 , nonzero [digits], nonzero [underscore] digits
• Hex : 0x(X) HexDigits [undersocre] HexDigits
• Octal : 0 OctalDigits [undersocre] OctalDigits
• Binary : 0b(B) BinaryDigits [undersocre] BinaryDigits
• Undersocre : use to denote digits, as comma in accounting, only between digits, can not be start or end
• Max pos int(32 bits) : 2^31 = 2147483647 / 0x7fff_ffff / 0177_7777_7777 / 0b0111_1111_1111_1111_1111_1111_1111_1111
• Max neg int : -2^31 = -2147483648

• Max long(64 bits) : 2^63

  Floating

  FloatingPointLiteral:
    DecimalFloatingPointLiteral
    HexadecimalFloatingPointLiteral
  DecimalFloatingPointLiteral:
    Digits . [Digits] [ExponentPart] [FloatTypeSuffix]
    . Digits [ExponentPart] [FloatTypeSuffix]
    Digits ExponentPart [FloatTypeSuffix]
    Digits [ExponentPart] FloatTypeSuffix
  ExponentPart:
    ExponentIndicator SignedInteger
  ExponentIndicator:
    (one of)
    e E
  SignedInteger:
    [Sign] Digits
  Sign:
    (one of)
    + -
  FloatTypeSuffix:
    (one of)
    f F d D

• Suffix : F for folat, D for double
• Infinities : 1f/0f, -1d/0d, POSITIVE_INFINITY, NEGATIVE_INFINITY

Boolean

ture/ false

Character

• enclosed in single quotes
• UTF-16 code units : \u0000 - \uffff
• Line Terminator not allowed : \u000a,\u000d ; use \n, \r instead

String

• enclosed in double quotes

• not accept : \u000a(LF), \u000d(CR) and \u0002(")

  package testPackage;
  class Test {
    public static void main(String[] args) {
        String hello = "Hello", lo = "lo";
        System.out.print((hello == "Hello") + " ");            //true
        System.out.print((Other.hello == hello) + " ");        //true
        System.out.print((other.Other.hello == hello) + " ");  //true
        System.out.print((hello == ("Hel"+"lo")) + " ");       //true, computed at compile
        System.out.print((hello == ("Hel"+lo)) + " ");         //fasle, computed as runtime
        System.out.println(hello == ("Hel"+lo).intern());      //true, use constant pool
    }
  }
  class Other { static String hello = "Hello"; }

• more compare : Strings

Escapes

EscapeSequence:
    \ b (backspace BS, Unicode \u0008)
    \ t (horizontal tab HT, Unicode \u0009)
    \ n (linefeed LF, Unicode \u000a)
    \ f (form feed FF, Unicode \u000c)
    \ r (carriage return CR, Unicode \u000d)
    \ " (double quote ", Unicode \u0022)
    \ ' (single quote ', Unicode \u0027)
    \ \ (backslash \, Unicode \u005c)
    OctalEscape (octal value, Unicode \u0000 to \u00ff)
OctalEscape:
    \ OctalDigit
    \ OctalDigit OctalDigit
    \ ZeroToThree OctalDigit OctalDigit
OctalDigit:
    (one of)
    0 1 2 3 4 5 6 7
ZeroToThree:
    (one of)
    0 1 2 3

Null

• null

Separators (Punctuators)

(   )   {   }   [   ]   ;   ,   .   ...   @   ::

• 12

Operators

=   >   <   !   ~   ?   :   ->
==  >=  <=  !=  &&  ||  ++  --
+   -   *   /   &   |   ^   %   <<   >>   >>>
+=  -=  *=  /=  &=  |=  ^=  %=  <<=  >>=  >>>=

• 38

Ref.

Lexical Structure

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