方案一：
class文件都是二进制的。
首先用vi 打开
然后输入%!xxd
显示其16进制格式
方案二：
javap -verbose xxx.class
例子
原始代码
public class SymjaException extends CalculatorException {
public SymjaException(String message, IExceptionType type) {
super(message, type);
}
}
字节码（16进制）
1 0000000: cafe babe 0000 0034 0014 0a00 0300 1107 .......4........
2 0000010: 0012 0700 1301 0006 3c69 6e69 743e 0100 ........<init>..
3 0000020: 4128 4c6a 6176 612f 6c61 6e67 2f53 7472 A(Ljava/lang/Str
4 0000030: 696e 673b 4c6f 7574 666f 782f 6361 6c63 ing;Loutfox/calc
5 0000040: 756c 6174 6f72 2f65 7863 6570 7469 6f6e ulator/exception
6 0000050: 2f49 4578 6365 7074 696f 6e54 7970 653b /IExceptionType;
7 0000060: 2956 0100 0443 6f64 6501 000f 4c69 6e65 )V...Code...Line
8 0000070: 4e75 6d62 6572 5461 626c 6501 0012 4c6f NumberTable...Lo
9 0000080: 6361 6c56 6172 6961 626c 6554 6162 6c65 calVariableTable
10 0000090: 0100 0474 6869 7301 002c 4c6f 7574 666f ...this..,Loutfo
11 00000a0: 782f 6361 6c63 756c 6174 6f72 2f65 7863 x/calculator/exc
12 00000b0: 6570 7469 6f6e 2f53 796d 6a61 4578 6365 eption/SymjaExce
13 00000c0: 7074 696f 6e3b 0100 076d 6573 7361 6765 ption;...message
14 00000d0: 0100 124c 6a61 7661 2f6c 616e 672f 5374 ...Ljava/lang/St
15 00000e0: 7269 6e67 3b01 0004 7479 7065 0100 2c4c ring;...type..,L
16 00000f0: 6f75 7466 6f78 2f63 616c 6375 6c61 746f outfox/calculato
17 0000100: 722f 6578 6365 7074 696f 6e2f 4945 7863 r/exception/IExc
18 0000110: 6570 7469 6f6e 5479 7065 3b01 000a 536f eptionType;...So
19 0000120: 7572 6365 4669 6c65 0100 1353 796d 6a61 urceFile...Symja
20 0000130: 4578 6365 7074 696f 6e2e 6a61 7661 0c00 Exception.java..
21 0000140: 0400 0501 002a 6f75 7466 6f78 2f63 616c .....*outfox/cal
22 0000150: 6375 6c61 746f 722f 6578 6365 7074 696f culator/exceptio
23 0000160: 6e2f 5379 6d6a 6145 7863 6570 7469 6f6e n/SymjaException
24 0000170: 0100 2f6f 7574 666f 782f 6361 6c63 756c ../outfox/calcul
25 0000180: 6174 6f72 2f65 7863 6570 7469 6f6e 2f43 ator/exception/C
26 0000190: 616c 6375 6c61 746f 7245 7863 6570 7469 alculatorExcepti
27 00001a0: 6f6e 0021 0002 0003 0000 0000 0001 0001 on.!............
28 00001b0: 0004 0005 0001 0006 0000 0049 0003 0003 ...........I....
29 00001c0: 0000 0007 2a2b 2cb7 0001 b100 0000 0200 ....*+,.........
30 00001d0: 0700 0000 0a00 0200 0000 1100 0600 1200 ................
31 00001e0: 0800 0000 2000 0300 0000 0700 0900 0a00 .... ...........
32 00001f0: 0000 0000 0700 0b00 0c00 0100 0000 0700 ................
33 0000200: 0d00 0e00 0200 0100 0f00 0000 0200 100a ................
javap
MD5 checksum 0ae899847b450473f19c09f6e38899e2
Compiled from "SymjaException.java"
public class outfox.calculator.exception.SymjaException extends outfox.calculator.exception.CalculatorException
minor version: 0
major version: 52
flags: ACC_PUBLIC, ACC_SUPER
Constant pool:
#1 = Methodref #3.#17 // outfox/calculator/exception/CalculatorException."<init>":(Ljava/lang/String;Loutfox/calculator/exception/IExceptionType;)V
#2 = Class #18 // outfox/calculator/exception/SymjaException
#3 = Class #19 // outfox/calculator/exception/CalculatorException
#4 = Utf8 <init>
#5 = Utf8 (Ljava/lang/String;Loutfox/calculator/exception/IExceptionType;)V
#6 = Utf8 Code
#7 = Utf8 LineNumberTable
#8 = Utf8 LocalVariableTable
#9 = Utf8 this
#10 = Utf8 Loutfox/calculator/exception/SymjaException;
#11 = Utf8 message
#12 = Utf8 Ljava/lang/String;
#13 = Utf8 type
#14 = Utf8 Loutfox/calculator/exception/IExceptionType;
#15 = Utf8 SourceFile
#16 = Utf8 SymjaException.java
#17 = NameAndType #4:#5 // "<init>":(Ljava/lang/String;Loutfox/calculator/exception/IExceptionType;)V
#18 = Utf8 outfox/calculator/exception/SymjaException
#19 = Utf8 outfox/calculator/exception/CalculatorException
{
public outfox.calculator.exception.SymjaException(java.lang.String, outfox.calculator.exception.IExceptionType);
descriptor: (Ljava/lang/String;Loutfox/calculator/exception/IExceptionType;)V
flags: ACC_PUBLIC
Code:
stack=3, locals=3, args_size=3
0: aload_0
1: aload_1
2: aload_2
3: invokespecial #1 // Method outfox/calculator/exception/CalculatorException."<init>":(Ljava/lang/String;Loutfox/calculator/exception/IExceptionType;)V
6: return
LineNumberTable:
line 17: 0
line 18: 6
LocalVariableTable:
Start Length Slot Name Signature
0 7 0 this Loutfox/calculator/exception/SymjaException;
0 7 1 message Ljava/lang/String;
0 7 2 type Loutfox/calculator/exception/IExceptionType;
}
SourceFile: "SymjaException.java"
可以根据字节码（16进制），一步步的读取一下数据。就能了解了。
简要分区
1、魔数，版本号
2、常量池
3、类索引，父类索引以及接口索引（3个0x0000这种格式表示）
4、字段（没有的话就是0x0000）比如上面的例子
5、方法（没有的话就是0x0000）
6、属性（会引用常量池的索引）
