The hexdump unix utility allows you to dump the contents of a
compiled/executable file in a readable hexadecimal format. Adding the -C
flag includes a sidebar with a formatted version of that row of hexadecimal.
For example, a compiled Hello World java program, Hello.java, will look
something like this:
> cat Hello.class | hexdump -C
00000000 ca fe ba be 00 00 00 34 00 1d 0a 00 06 00 0f 09 |.......4........|
00000010 00 10 00 11 08 00 12 0a 00 13 00 14 07 00 15 07 |................|
00000020 00 16 01 00 06 3c 69 6e 69 74 3e 01 00 03 28 29 |.....<init>...()|
00000030 56 01 00 04 43 6f 64 65 01 00 0f 4c 69 6e 65 4e |V...Code...LineN|
00000040 75 6d 62 65 72 54 61 62 6c 65 01 00 04 6d 61 69 |umberTable...mai|
00000050 6e 01 00 16 28 5b 4c 6a 61 76 61 2f 6c 61 6e 67 |n...([Ljava/lang|
00000060 2f 53 74 72 69 6e 67 3b 29 56 01 00 0a 53 6f 75 |/String;)V...Sou|
00000070 72 63 65 46 69 6c 65 01 00 0a 48 65 6c 6c 6f 2e |rceFile...Hello.|
00000080 6a 61 76 61 0c 00 07 00 08 07 00 17 0c 00 18 00 |java............|
00000090 19 01 00 0d 48 65 6c 6c 6f 2c 20 57 6f 72 6c 64 |....Hello, World|
000000a0 21 07 00 1a 0c 00 1b 00 1c 01 00 05 48 65 6c 6c |!...........Hell|
000000b0 6f 01 00 10 6a 61 76 61 2f 6c 61 6e 67 2f 4f 62 |o...java/lang/Ob|
000000c0 6a 65 63 74 01 00 10 6a 61 76 61 2f 6c 61 6e 67 |ject...java/lang|
000000d0 2f 53 79 73 74 65 6d 01 00 03 6f 75 74 01 00 15 |/System...out...|
000000e0 4c 6a 61 76 61 2f 69 6f 2f 50 72 69 6e 74 53 74 |Ljava/io/PrintSt|
000000f0 72 65 61 6d 3b 01 00 13 6a 61 76 61 2f 69 6f 2f |ream;...java/io/|
00000100 50 72 69 6e 74 53 74 72 65 61 6d 01 00 07 70 72 |PrintStream...pr|
00000110 69 6e 74 6c 6e 01 00 15 28 4c 6a 61 76 61 2f 6c |intln...(Ljava/l|
00000120 61 6e 67 2f 53 74 72 69 6e 67 3b 29 56 00 20 00 |ang/String;)V. .|
00000130 05 00 06 00 00 00 00 00 02 00 00 00 07 00 08 00 |................|
00000140 01 00 09 00 00 00 1d 00 01 00 01 00 00 00 05 2a |...............*|
00000150 b7 00 01 b1 00 00 00 01 00 0a 00 00 00 06 00 01 |................|
00000160 00 00 00 01 00 09 00 0b 00 0c 00 01 00 09 00 00 |................|
00000170 00 25 00 02 00 01 00 00 00 09 b2 00 02 12 03 b6 |.%..............|
00000180 00 04 b1 00 00 00 01 00 0a 00 00 00 0a 00 02 00 |................|
00000190 00 00 03 00 08 00 04 00 01 00 0d 00 00 00 02 00 |................|
000001a0 0e |.|
000001a1