K.I.S.S

CONSTANT_Class_info {
  u1 tag;
  u2 name_index;
}

注意,这里代表的是cp_{info的整个},所以也包括了tag.name\_{index则代表的具体的名称的index},具体的名称同样也会在pool里面,指向的类型应该是 CONSTANT\_Utf8\info 的类型.

数组也是对象,表示形式比较特殊:

int[][] => [[I
Thread[] => [Ljava/lang/Thread;

An array type descriptor is valid only if it represents 255 or fewer dimensions.

这句是什么意思呢?最多只支持255维度?

*代表的是Field/Method/Interface,这几个结构一致.

CONSTANT_*ref_info {
  u1 tag;
  u2 class_index;
  u2 name_and_type_index;
}

CONSTANT_String_info {
  u1 tag;
  u2 string_index;
}

比较简单,index指向的必须是 CONSTANT\_Utf8\info

CONSTANT_*_info {
  u1 tag;
  u4 bytes;
}

bytes中保存是常量的值,其中float的是IEEE 754 floating-point single format.都是big-endian. 表示float的value,首先转换为int,直接引用:

• If bits is 0x7f800000, the float value will be positive infinity.
• If bits is 0xff800000, the float value will be negative infinity.
• If bits is in the range 0x7f800001 through 0x7fffffff or in the range 0xff800001 through 0xffffffff, the float value will be NaN.
• In all other cases, let s, e, and m be three values that might be computed from bits:
  • int s = ((bits >> 31) == 0) ? 1 : -1;
  • int e = ((bits >> 23) & 0xff);
  • int m = (e == 0) ? (bits & 0x7fffff) << 1 : (bits & 0x7fffff) | 0x800000;
  • Then the float value equals the result of the mathematical expression . s * m* 2^(e-150)

CONSTANT_*_info {
  u1 tag;
  u4 high_bytes;
  u4 low_bytes;
}

这里计算index有个特殊情况,这两个结构一次占用两个位置.

All 8-byte constants take up two entries in the constant_pool table of the class
file. If a CONSTANT_Long_info or CONSTANT_Double_info structure is the item
in the constant_pool table at index n, then the next usable item in the pool is
located at index n +2. The constant_pool index n +1 must be valid but is
considered unusable.

基本类似上面的integer和float,只不过长度加多了.有关double的确定也是一样:

• If bits is 0x7ff0000000000000L, the double value will be positive infinity.
• If bits is 0xfff0000000000000L, the double value will be negative infinity.
• If bits is in the range 0x7ff0000000000001L through 0x7fffffffffffffffL or in the range 0xfff0000000000001L through 0xffffffffffffffffL, the double value will be NaN.
• In all other cases, let s, e, and m be three values that might be computed from bits:
  • int s = ((bits >> 63) == 0) ? 1 : -1;
  • int e = (int)((bits >> 52) & 0x7ffL);
  • long m = (e == 0) ? (bits & 0xfffffffffffffL) << 1 : (bits & 0xfffffffffffffL) | 0x10000000000000L;
  • Then the floating-point value equals the double value of the mathematical expression s*m*2^(e-1075)

CONSTANT_NameAndType_info {
  u1 tag;
  u2 name_index;
  u2 descriptor_index;
}

index指向的都是 CONSTANT\_Utf8\info,一个是名字,一个是 descriptor.

The CONSTANT\_Utf8\info structure is used to represent constant string values.String content is encoded in modified UTF-8.

和标准的UTF-8有小不同:

There are two differences between this format and the “standard” UTF-8 format. First, the null character (char)0 is encoded using the 2-byte format rather than the 1-byte format, so that modified UTF-8 strings never have embedded nulls. Second, only the 1-byte, 2-byte, and 3-byte formats of standard UTF-8 are used. The Java VM does not recognize the four-byte format of standard UTF-8; it uses its own two-times-three-byte format instead.

结构如下:

CONSTANT_Utf8_info {
  u1 tag;
  u2 length;
  u1 bytes[length];
}

没有可以多废话,很明显,限制条件是,不能是0 和 range(0xf0, 0xff)⁴

field_info {
 u2 access_flags;
 u2 name_index;
 u2 descriptor_index;
 u2 attributes_count;
 attribute_info attributes[attributes_count];
}

主要就是 attribute\_info ,结构:

attribute_info {
  u2 attribute_name_index;
  u4 attribute_length;
  u1 info[attribute_length];
}

有predefined的,SourceFile,ConstantValue,Code,StackMapTable,Exceptions,InnerClasses,EnclosingMethod, Synthetic, Signature, LineNumberTable, LocalVariableTable and Deprecated…后面太多了,不看了.