RE: JavaVM description

> theUser BL wrote:
> > Hi!
> 
> > But where can I find documentations about .class files? How are they are
> > structures and so on?
> 
> In the JVM specification, 2nd edition, for example. There is quite a
> bunch of literature explaining the workings of bytecode and the class
> file format, depending on the background you're after, from compiler
> design books, over interactive introductions, to formal methods.

Thx. It helps, but not much.
I have written  a little HelloWorld program in Java and have then treied to understand the created binary.
The most things I understand, but there are three big fields where I don't know for what they are. But if I change there a bit, the program will not run, so that areas seens to be important.
To understand it, I have written a little QBasic, program which generates that .class file. But as I said, there are the three big areas (one with 34 bytes and two with 39 bytes at a time) , which I don't understand.

------------------------------------

DECLARE FUNCTION invokespecial$ (a&)
DECLARE FUNCTION invokevirtual$ (a&)
DECLARE FUNCTION ldc$ (a%)
DECLARE FUNCTION getstatic$ (a&)
DECLARE FUNCTION LStr$ (name$)
DECLARE FUNCTION unhex$ (hexa$)
aload0$ = CHR$(42)
return$ = CHR$(177)
CLS
OPEN "HW.dat" FOR OUTPUT AS #1
PRINT #1, ""
CLOSE #1
OPEN "HW.dat" FOR BINARY AS #1
co$ = ""
co$ = co$ + unhex$("CAFEBABE")
co$ = co$ + unhex$("00000032")                  ' Classversion Number 0x32=50

co$ = co$ + unhex$("0024")                      'Length of the now comming field+1

co$ = co$ + unhex$("0A00090012")                '0x01 'java/lang/Object."<init>":()V
co$ = co$ + unhex$("0900130014")                '0x02 'java/lang/System.out:Ljava/io/PrintStream;
co$ = co$ + unhex$("080015")                    '0x03 'der erste Text,
co$ = co$ + unhex$("0A00160017")                '0x04 'java/io/PrintStream.println:(Ljava/lang/String;)V
co$ = co$ + unhex$("080018")                    '0x05 'der zweite Text
co$ = co$ + unhex$("0A00160019")                '0x06 'java/io/PrintStream.print:(Ljava/lang/String;)V
co$ = co$ + unhex$("08001A")                    '0x07 'und der dritte Text.
co$ = co$ + unhex$("07001B")                    '0x08 'HalloWelt
co$ = co$ + unhex$("07001C")                    '0x09 'java/lang/Object
co$ = co$ + LStr$("<init>")                     '0x0A
co$ = co$ + LStr$("()V")                        '0x0B
co$ = co$ + LStr$("Code")                       '0x0C
co$ = co$ + LStr$("LineNumberTable")            '0x0D
co$ = co$ + LStr$("main")                       '0x0E
co$ = co$ + LStr$("([Ljava/lang/String;)V")     '0x0F
co$ = co$ + LStr$("SourceFile")                 '0x10
co$ = co$ + LStr$("HalloWelt.java")             '0x11
co$ = co$ + unhex$("0C000A000B")                '0x12 '"<init>":()V
co$ = co$ + unhex$("07001D")                    '0x13 'java/lang/System.
co$ = co$ + unhex$("0C001E001F")                '0x14 'out:Ljava/io/PrintStream;
co$ = co$ + LStr$("der erste Text,")            '0x15
co$ = co$ + unhex$("070020")                    '0x16 'java/io/PrintStream.
co$ = co$ + unhex$("0C00210022")                '0x17 'println:(Ljava/lang/String;)V
co$ = co$ + LStr$("der zweite Text ")           '0x18
co$ = co$ + unhex$("0C00230022")                '0x19 'print:(Ljava/lang/String;)V
co$ = co$ + LStr$("und der dritte Text.")       '0x1A
co$ = co$ + LStr$("HalloWelt")                  '0x1B
co$ = co$ + LStr$("java/lang/Object")           '0x1C
co$ = co$ + LStr$("java/lang/System")           '0x1D
co$ = co$ + LStr$("out")                        '0x1E
co$ = co$ + LStr$("Ljava/io/PrintStream;")      '0x1F
co$ = co$ + LStr$("java/io/PrintStream")        '0x20
co$ = co$ + LStr$("println")                    '0x21
co$ = co$ + LStr$("(Ljava/lang/String;)V")      '0x22
co$ = co$ + LStr$("print")                      '0x23

co$ = co$ + unhex$("0020000800090000000000020000000A")  ' for what is this ??? possible is the 0x20=32 the number of bytes until
co$ = co$ + unhex$("000B0001000C0000001D000100010000")  ' the first assembler code. But what is with the rest?
co$ = co$ + unhex$("0005")

co$ = co$ + aload0$
co$ = co$ + invokespecial$(1)
co$ = co$ + return$

co$ = co$ + unhex$("00000001000D00000006000100000001")  ' and for what this ???
co$ = co$ + unhex$("0009000E000F0001000C0000003D0002")
co$ = co$ + unhex$("000100000019")

co$ = co$ + getstatic$(2)
co$ = co$ + ldc$(3)
co$ = co$ + invokevirtual$(4)
co$ = co$ + getstatic$(2)
co$ = co$ + ldc$(5)
co$ = co$ + invokevirtual$(6)
co$ = co$ + getstatic$(2)
co$ = co$ + ldc$(7)
co$ = co$ + invokevirtual$(4)
co$ = co$ + return$

co$ = co$ + unhex$("00000001000D00000012000400000003")  ' and this ???
co$ = co$ + unhex$("00080004001000050018000600010010")
co$ = co$ + unhex$("000000020011")


PUT #1, 1, co$
CLOSE #1

SHELL "xcopy /y HW.dat HalloWelt.class"
SHELL "java HalloWelt"
'SHELL "c:\Progra~1\java\jdk16~1.0_1\bin\javap.exe -c HalloWelt"

FUNCTION getstatic$ (a&)
IF a& > 65535 THEN PRINT "*** Error": END
a1& = INT(a& / 256)
a2& = a& - a1& * 256
getstatic$ = CHR$(178) + CHR$(a1&) + CHR$(a2&)
END FUNCTION

FUNCTION invokespecial$ (a&)
IF a& > 65535 THEN PRINT "*** Error": END
a1& = INT(a& / 256)
a2& = a& - a1& * 256
invokespecial$ = CHR$(183) + CHR$(a1&) + CHR$(a2&)
END FUNCTION

FUNCTION invokevirtual$ (a&)
IF a& > 65535 THEN PRINT "*** Error": END
a1& = INT(a& / 256)
a2& = a& - a1& * 256
invokevirtual$ = CHR$(182) + CHR$(a1&) + CHR$(a2&)
END FUNCTION

FUNCTION ldc$ (a%)
IF a% > 255 THEN PRINT "*** Error": END
ldc$ = CHR$(18) + CHR$(a%)
END FUNCTION

FUNCTION LStr$ (name$)
' gives out the length of name$ as character and adds the name$ to it

a& = LEN(name$)
IF a& > 65535 THEN PRINT "*** Error": END
a1& = INT(a& / 256)
a2& = a& - a1& * 256

LStr$ = CHR$(1) + CHR$(a1&) + CHR$(a2&) + name$

END FUNCTION

FUNCTION unhex$ (hexa$)

uhex$ = ""

FOR i = 1 TO LEN(hexa$) / 2
 ahex$ = MID$(hexa$, i * 2 - 1, 1)
  IF ahex$ = "0" THEN abyte% = 0
  IF ahex$ = "1" THEN abyte% = 1
  IF ahex$ = "2" THEN abyte% = 2
  IF ahex$ = "3" THEN abyte% = 3
  IF ahex$ = "4" THEN abyte% = 4
  IF ahex$ = "5" THEN abyte% = 5
  IF ahex$ = "6" THEN abyte% = 6
  IF ahex$ = "7" THEN abyte% = 7
  IF ahex$ = "8" THEN abyte% = 8
  IF ahex$ = "9" THEN abyte% = 9
  IF ahex$ = "A" THEN abyte% = 10
  IF ahex$ = "B" THEN abyte% = 11
  IF ahex$ = "C" THEN abyte% = 12
  IF ahex$ = "D" THEN abyte% = 13
  IF ahex$ = "E" THEN abyte% = 14
  IF ahex$ = "F" THEN abyte% = 15

 bhex$ = MID$(hexa$, i * 2, 1)
  IF bhex$ = "0" THEN bbyte% = 0
  IF bhex$ = "1" THEN bbyte% = 1
  IF bhex$ = "2" THEN bbyte% = 2
  IF bhex$ = "3" THEN bbyte% = 3
  IF bhex$ = "4" THEN bbyte% = 4
  IF bhex$ = "5" THEN bbyte% = 5
  IF bhex$ = "6" THEN bbyte% = 6
  IF bhex$ = "7" THEN bbyte% = 7
  IF bhex$ = "8" THEN bbyte% = 8
  IF bhex$ = "9" THEN bbyte% = 9
  IF bhex$ = "A" THEN bbyte% = 10
  IF bhex$ = "B" THEN bbyte% = 11
  IF bhex$ = "C" THEN bbyte% = 12
  IF bhex$ = "D" THEN bbyte% = 13
  IF bhex$ = "E" THEN bbyte% = 14
  IF bhex$ = "F" THEN bbyte% = 15

uhex$ = uhex$ + CHR$(abyte% * 16 + bbyte%)
NEXT i
unhex$ = uhex$
END FUNCTION



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