Definition: u11 bytes are non-negative values. u22 bytes are non-negative values ........ (others) the Java file structure is described as follows using struct: ClassFile {u4magic; must be 0xCAFEBABEu2minor_version; u2major_version; CLASS file structure primary and secondary version JA
Definition: u1 1 byte is the unit of non-negative value u2 2 byte is the unit of non-negative value u3 ........ (others) the Java file structure is described as follows using struct: ClassFile {u4 magic; // It must be 0 xCAFEBABE u2 minor_version; u2 major_version; // The primary and secondary versions of the CLASS file structure JA
Definition: u1
1 byte is a non-negative value in units
U2
The two bytes are non-negative values in units.
U3
........
(Others, and so on)
Java
File
StructureA description similar to struct is as follows:
ClassFile {
U4 magic;
// The value must be 0 xCAFEBABE.
U2 minor_version;
U2 major_version;
// CLASS
File
StructureMajor and minor version JAVA2 supports 45.0-46.
0
U2 constant_pool_count; // record constant information
Cp_info constant_pool [constant_pool_count-1];
// The count starts from 1.
U2 access_flags;
// Class/interface access permission
U2 this_class;
// Point to the valid index value in constant_poll
U2 super_class;
// 0 or point to the valid index value in constant_poll.
Terface must be non-0
U2 interfaces_count;
// Number of superinterfaces
U2 interfaces [interfaces_count];
// Count [0, count-1) corresponding to constant_po
An index value in ol
U2 fields_count;
Field_info fields [fields_count];
// Used to record class and instance variables
U2 methods_count;
Method_info methods [methods_count];
U2 attributes_count;
Attribute_info attributes [attributes_count];
}
Cp_info {
U1 tag;
U1 info [];
}
The tag has the following meanings:
CONSTANT_Class
7
CONSTANT_Fieldref
9
CONSTANT_Methodref
10
CONSTANT_InterfaceMethodref
11
CONSTANT_String
8
CONSTANT_Integer
3
CONSTANT_Float
4
CONSTANT_Long
5
CONSTANT_Double
6
CONSTANT_NameAndType
12
CONSTANT_Utf8
1
Cp_info corresponds
StructureChanged
1. CONSTANT_Class
CONSTANT_Class_info {
U1 tag;
U2 name_index;
}
2. CONSTANT_Fieldref
CONSTANT_Fieldref_info {
U1 tag;
U2 class_index;
// Constant_pool index, corresponding to CONSTANT_Class _
Info
U2 name_and_type_index; // constant_pool index, corresponding to CONSTANT _
NameAndType_info
}
3. CONSTANT_Methodref
CONSTANT_Methodref_info {
U1 tag;
U2 class_index;
U2 name_and_type_index;
}
4. CONSTANT_InterfaceMethodref
CONSTANT_InterfaceMethodref_info {
U1 tag;
U2 class_index;
U2 name_and_type_index;
}
5. CONSTANT_String
CONSTANT_String_info {
U1 tag;
U2 string_index;
}
6. CONSTANT_Integer
CONSTANT_Integer_info {
U1 tag;
U4 bytes;
}
7. CONSTANT_Float
CONSTANT_Float_info {
U1 tag;
U4 bytes;
}
8. CONSTANT_Long
CONSTANT_Long_info {
U1 tag;
U4 high_bytes;
U4 low_bytes;
}
9. CONSTANT_Double
CONSTANT_Double_info {
U1 tag;
U4 high_bytes;
U4 low_bytes
}
10. CONSTANT_NameAndType
CONSTANT_NameAndType_info {
U1 tag;
U2 name_index;
U2 descriptor_index;
}
11. CONSTANT_Utf8
CONSTANT_Utf8_info {
U1 tag;
U2 length;
U1 bytes [length];
}
Access_flags indicates the following:
ACC_PUBLIC
Zero x 0001
ACC_FINAL
Zero x 0010
ACC_SUPER
Zero x 0020
ACC_INTERFACE
Zero x 0200
ACC_ABSTRACT
Zero x 0400
If it is an interface, you must set ACC_INTERFACE. If it is not set to an ACC_INTERFACE, it is defined as one.
Instead of interfaces.
If ACC_INTERFACE is set, the ACC_ABSTRACT bit must also be set. You can also set the AC
C_PUBLIC.
ACC_SUPER is used to indicate invokespecial semantics. Sun's old JAVA compiler does not set ACC_SUPER
And the old JVM
The ACC_SUPER bit is ignored, but the new compiler should implement the invokespecial semantics.
Other unspecified bits are reserved for future use, and the compiler should set them to 0.
Click them.
This_class:
The index value in constant_pool. The cp_info of the element to which it points is equivalent to CONSTANT_Class.
_ Info
CONSTANT_Class_info {
U1 tag;
// The value must be CONSTANT_Class (7)
U2 name_index;
// Point to an index value in constant_pool
}
Name_index: cp_info is equivalent to CONSTANT_Utf8_info.
CONSTANT_Utf8_info {
U1 tag;
// The value must be CONSTANT_Utf8 (1)
U2 length;
U1 bytes [length];
// Utf8 encoded string
}
Field_info {
U2 access_flags;
// Access Control
U2 name_index;
// Index in constant_pool, corresponding to CONSTANT_Utf8_inf
O description.
U2 descriptor_index; // The index in constant_pool, corresponding to CONSTANT_Utf8_ I
Nfo description.
U2 attributes_count;
Attribute_info attributes [attributes_count]; // attribute_info will be stored in mo
Description after thods.
}
The value of access_flages in field_info is as follows:
ACC_PUBLIC
Zero x 0001
ACC_PRIVATE
Zero x 0002
ACC_PROTECTED
Zero x 0004
ACC_STATIC
Zero x 0008
ACC_FINAL
Zero x 0010
ACC_VOLATILE
Zero x 0040
ACC_TRANSIENT
Zero x 0080
Obviously, the ACC_FINAL and ACC_VOLATILE cannot be used at the same time, and the first three are mutually exclusive.
The interface must be set to the ACC_PUBLIC, ACC_STATIC, and ACC_FINAL bits, and cannot be set to other bits.
Other unspecified bits are retained for future use, and the compiler should set it to 0.
When ignoring them.
Methods indicates all methods in the class.
Method_info {
U2 access_flags;
U2 name_index;
// Point to the constant_pool entry, corresponding to CONSTANT _
Utf8_info
U2 descriptor_index;
// Point to the constant_pool entry, corresponding to CONS
TANT_Utf8_info
U2 attributes_count;
Attribute_info attributes [attributes_count];
// Only four types of codes, Exceptions, Synthetic, and Deprecated can appear here
Type attributes
}
Access_flags access permissions are described as follows:
ACC_PUBLIC
Zero x 0001
ACC_PRIVATE
Zero x 0002
ACC_PROTECTED
Zero x 0004
ACC_STATIC
Zero x 0008
ACC_FINAL
Zero x 0010
ACC_SYNCHRONIZED
Zero x 0020
ACC_NATIVE
Zero x 0100
ACC_ABSTRACT
Zero x 0400
ACC_STRICT
Zero x 0800
Attribute_info {
U2 attribute_name_index;
// Index in constant_pool, corresponding to CONSTANT_U
Tf8_info description.
U4 attribute_length;
U1 info [attribute_length];
}
Predefined attributes include:
1. SourceFile: attribute_info is replaced:
SourceFile_attribute {
U2 attribute_name_index;
U4 attribute_length;
U2 sourcefile_index; // point to a CONSTANT_Ut in constant_pool
F8_info
Structure.
}
2. Constantvalue: attribute_info is replaced:
Constantvalue_attribute {
U2 attribute_name_index;
U4 attribute_length;
// It must be 2
U2 constantvalue_index;
}
Constantvalue_index has the following meanings:
Long
CONSTANT_Long
Float
CONSTANT_Float
Double
CONSTANT_Double
Int, short, char, byte, boolean
CONSTANT_Integer
String
CONSTANT_String
Constantvalue is used in field_info to describe a static constant,
In this case, the access_flags of field_info should be ACC_STATIC.
3. Code: attribute_info is replaced:
Code_attribute {
U2 attribute_name_index;
U4 attribute_length;
U2 max_stack;
// Maximum stack depth available when executing this function
U2 max_locals; // The maximum number of local variables available for executing this function, including Parameters
Number.
// Note: A long/double is equivalent to the number of two variables.
U4 code_length; // The code length used by this function.
U1 code [code_length]; // The Real bytecode used to implement this function
U2 prediction_table_length;
{
U2 start_pc;
U2 end_pc; // [start_pc, end_p
C) Part
U2
Handler_pc; // What does handler_pc do !!
U2
Catch_type; // The index pointing to the constant_pool, corresponding to the CONSTANT
_ Class_info
} Prediction_table [prediction_table_length];
