> 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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