----( Java .class file structure )----------------------------------------------

this gives a hint on how the java .class files are structured. for 
details see the Java VM Specification.

supporting files can be found on http://plain.at/vpavlu/class/



ClassFile {
	u4 magic = 0xCAFEBABE;
	u2 minor_version;        //class file version
	u2 major_version;        //class file version
	u2 constant_pool_count;  // number of cp_info elems (1 = empty pool) indexed by 1..N-1
	cp_info constant_pool[constant_pool_count-1];
	u2 access_flags;
	u2 this_class;           //valid index to CONSTANT_Class_info elem in constant_pool
	u2 super_class;          //like this_class or zero (but then this class must be the class Object)
	u2 interfaces_count;     //number of super interfaces 0..N-1
	u2 interfaces[interfaces_count];
	u2 fields_count;         //number of class/instance variables (not inherited ones)
	field_info fields[fields_count];
	u2 methods_count;        //number of methods (not inherited ones)
	method_info methods[methods_count];
	u2 attributes_count;     //number of attributes (SourceFile, Deprecated, ...)
	attribute_info attributes[attributes_count];
}


-- CONSTANT POOL (cp.c) --

cp_info {
  u1 tag;
  u1 info[];
}

    derived type                  cp_info.tag
    -----------------------------------------
    CONSTANT_Utf8 	              1
    CONSTANT_Integer 	            3
    CONSTANT_Float 	              4
    CONSTANT_Long 	              5
    CONSTANT_Double 	            6
    CONSTANT_Class 	              7
    CONSTANT_String 	            8
    CONSTANT_Fieldref 	          9
    CONSTANT_Methodref 	          10
    CONSTANT_InterfaceMethodref 	11
    CONSTANT_NameAndType 	        12


cp_info derived types:  


CONSTANT_Utf8_info {
  u1 tag=1;
  u2 bytes_length;  //number of bytes (not null-terminated)
  u1 bytes[length];
}

CONSTANT_Integer_info { //or Float
  u1 tag;    //3 (int), or 4 (float)
  u4 bytes;  //big-endian bytes determining value
}

CONSTANT_Long_info { //or Double
  u1 tag;        //5 (long), 6 (double)
  u4 high_bytes;
  u4 low_bytes;
}

CONSTANT_Class_info {
  u1 tag=7;
  u2 name_index;  //CONSTANT_Utf8_info in cp
}

CONSTANT_String_info {
  u1 tag=8;
  u2 string_index;  //CONSTANT_Utf8_info in cp
}

CONSTANT_XXXref_info {    //XXX = {Field|Method|InterfaceMethod}
  u1 tag;                 //9, 10, or 11
  u2 class_index;         //CONSTANT_Class_info in cp
  u2 name_and_type_index; //CONSTANT_NameAndType_info in cp
}

CONSTANT_NameAndType_info {
  u1 tag=12;
  u2 name_index;       //CONSTANT_Utf8_info in cp
  u2 descriptor_index; //CONSTANT_Utf8_info in cp
}



-- FIELDS (members.c) --

field_info {
	u2 access_flags;     //access permission
	u2 name_index;       //CONSTANT_Utf8_info (name) in cp
	u2 descriptor_index; //CONSTANT_Utf8_info (field descriptor) in cp
	u2 attributes_count;
	attribute_info attributes[attributes_count];
}



-- ACCESS MODIFER (access.c) --

ACC_PUBLIC -- 0x0001, accessed from outside package
ACC_PRIVATE -- 0x0002, only within defining class
ACC_PROTECTED -- 0x0004, within subclasses
ACC_STATIC -- 0x0008, static (class variable)
ACC_FINAL -- 0x0010, no further assignment after initialization

additional for fields

ACC_VOLATILE -- 0x0040, cannot be cached (FIELDS)
ACC_TRANSIENT -- 0x0080, not written/read by persistent object manager (FIELDS)

additional for methods

ACC_SYNCHRONIZED -- 0x0020, invocation is wrapped in monitor lock
ACC_NATIVE -- 0x0100, implemented in  non-java
ACC_ABSTRACT -- 0x0400, no implementation
ACC_STRICT -- 0x0800, floating-point mode is strict FP




-- METHODS (members.c) --

method_info {
	u2 access_flags;     //access permission
	u2 name_index;       //CONSTANT_Utf8_info (name, <init>, <clinit>) in cp
	u2 descriptor_index; //CONSTANT_Utf8_info (method descriptor) in cp
	u2 attributes_count;
	attribute_info attributes[attributes_count];
}

-- ATTRIBUTES --

attribute_info {
	u2 attribute_name_index;   //CONSTANT_Utf8_info (name) in cp
	u4 attribute_length;       //length in bytes
	u1 info[attribute_length]; //array of attribute bytes
}


attribute_info derived types:


ConstantValue_attribute {
  u2 attribute_name_index; //CONSTANT_Utf8_info ("ConstantValue") in cp
  u4 attribute_length;
  u2 constantvalue_index;  //CONSTANT_XXX (the value) in cp
}

Code_attribute {
  u2 attribute_name_index;   //CONSTANT_Utf8_info ("Code") in cp
  u4 attribute_length;       //length without initial 6 bytes
  u2 max_stack;              //max depth of stack at any point
  u2 max_locals;             //number of locals and params
  u4 code_length;            //>0 bytes in code array
  u1 code[code_length];      //byte code instructions
  u2 exception_table_length; //number of entries in exception table
  {
    u2 start_pc;     //starting program counter (valid index in code)
    u2 end_pc;       //first pc value where execption is inactive (>start_pc, max code_length)
    u2 handler_pc;   //index in code, specifying the entry point for exception handler
    u2 catch_type;   //zero or CONSTANT_Class_info in cp giving exception type
  } exception_table[exception_table_length];  
  u2 attributes_count;       //attributes of code
  attribute_info attributes[attributes_count];
}


Exceptions_attribute {
  u2 attribute_name_index;  //CONSTANT_Utf8_info ("Exceptions") in cp
  u4 attribute_length;      //length without initial 6 bytes
  u2 number_of_exceptions;
  u2 exception_index_table[number_of_exceptions];
}


InnerClasses_attribute {
	u2 attribute_name_index;
	u4 attribute_length;
	u2 number_of_classes;
	{  u2 inner_class_info_index;	     
	   u2 outer_class_info_index;	     
	   u2 inner_name_index;	     
	   u2 inner_class_access_flags;	     
	} classes[number_of_classes];
}


SourceFile_attribute {
	u2 attribute_name_index;
	u4 attribute_length;
	u2 sourcefile_index;  //CONSTANT_Utf8_info in cp
}


LineNumberTable_attribute {
	u2 attribute_name_index;
	u4 attribute_length;
	u2 line_number_table_length;
	{  u2 start_pc;
	   u2 line_number;
	} line_number_table[line_number_table_length];
}


LocalVariableTable_attribute {
	u2 attribute_name_index;
	u4 attribute_length;
	u2 local_variable_table_length;
	{  u2 start_pc;
	    u2 length;
	    u2 name_index;
	    u2 descriptor_index;
	    u2 index;
	} local_variable_table[local_variable_table_length];
}	

---------------------------------------------------------(vpavlu, 22May2004)----