JAVA - KLASSENDATEIEN

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JAVA - KLASSENDATEIEN

Seminarvortrag von

Studierach Beatrix

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Überblick

 Klassendatei

 Spezielle Strings

 Constant Pool

 Attribute

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Class-File

Programm in Java Programm

in anderer Sprache Programm

in Java

Compiler Compiler

Compiler

Java class

files Java class

files Other binary

format

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Typen

1. PRIMITIVE TYPEN:

 u1 ...1 unsigned byte

 u2 ... 2 unsigned bytes

 u4 ... 4 unsigned bytes

 u8 ... 8 unsigned bytes 2. TABELLENNAME

Big Endian

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Klassendatei - Struktur

ClassFile{

u4 magic;

u2 minor_version;

u2 major_version;

u2 constant_pool_count;

cp_info constant_pool [constant_pool_count-1];

u2 access_flags u2 this_class;

u2 super_class;

u2 interfaces_count;

u2 interfaces[interfaces_count];

u2 fields_count;

field_info fields[fields_count];

u2 methods_count;

method_info methods[methods_count];

u2 attributes_count;

attributte_info attributes[attributes_count];

Magic Number: 0xCAFEBABE

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Beispiele zur Version

 JDK 1.0.2 unterstützt Klassendatei- Formate der Versionen 45.0 bis 45.3

 SDK 1.2 unterstützt Klassendatei- Formate der Versionen 45.0 bis 46.0

Versionsnummer: 45.3

Major version no. Minor version no.

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Klassendatei - Struktur

ClassFile{

u4 magic; 

u2 minor_version;  u2 major_version;  u2 constant_pool_count;

cp_info constant_pool [constant_pool_count-1];

u2 access_flags u2 this_class;

u2 super_class;

u2 fields_count;

field_info fields [fields_count];

u2 methods_count;

attributte_info attributes[attributes_count];

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Constant Pool

Tag: CONSTANT_Class name_index: 7

Tag: CONSTANT_Utf8_info length: 3

This_class: 1 bytes: „Act“

constant_pool Entry #1

constant_pool Entry #7

this class

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Klassendatei - Struktur

ClassFile{

u4 magic; 

u2 minor_version;  u2 major_version; 

u2 constant_pool_count; 

cp_info constant_pool [constant_pool_count-1];  u2 access_flags

u2 this_class;

u2 super_class;

u2 fields_count;

field_info fields[fields_count];

u2 methods_count;

attribute_info attributes[attributes_count];

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Access_flags

Flag Name Bedeutung Verwendung

ACC_PUBLIC Zugriff ausserhalb des

Package möglich Klasse, Interface

ACC_FINAL Keine Unterklassen

erlaubt Klasse

ACC_SUPER Hat geerbte Methoden Klasse, Interface

ACC_INTERFACE Ist ein Interface Interface

ACC_ABSTRACT Ist Abstract und kann nicht

instanziert werden Klasse, Interface

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Überblick

 Klassendatei ^

 Spezielle Strings

 Constant Pool

 Attribute

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Spezielle Strings

 Fully qualified Names

 Simple Names

 Descriptors

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Fully qualified names

 Source Code:

– java.lang.Thread

 Class File:

– java/lang/Thread

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Simple names

 Constant Pool Eintrag der auf die Methode String toString() verweist:

– „toString“

 Constant Pool Eintrag der auf das Feld java.io.PrintStram out verweist:

– „out“

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Descriptors

FieldDescriptor:

FieldType ComponentType:

FieldType FieldType:

BaseType ObjectType ArrayType BaseType:

B C D F I J S Z

ObjectType:

L<classname>

ArrayType:

[ ComponentType MethodDesciptor:

( ParameterDesciptor * ) ReturnDesciptor ObjectType

ArrayType ParameterDesciptor:

FieldType ReturnDesciptor:

FieldType V

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Beispiele - Field Desciptor

int i;  I

long [][] windingRoad;  [[J

java.lang.Object[] stuff  [Ljava/lang/Object

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Beispiel – MethodDescriptor

 int getSize;

 ()I

 void main(String [] args);

 ([Ljava/lang/String;)V

 boolean regionMatches(boolean ignoreCase, int toOffset, String other, int offset, int len);

 (ZILjava/lang/Srting;II)Z

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Überblick

 Klassendatei ^

 Spezielle Strings ^

 Constant Pool

 Attribute

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Constant Pool

– Allgemeines Format

cp_ info { u1 tag;

u1 info[];

}

tag – Indikator für Typ des Eintrags

info – Inhalt variert mit Wert des Tags

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Constant Pool - Tag



CONSTANT_Class



CONSTANT_Fieldref



CONSTANT_Methodref



CONSTANT_InterfaceMethodref



CONSTANT_String



CONSTANT_Integer



CONSTANT_Float



CONSTANT_Long



CONSTANT_Double



CONSTANT_NameAndType



CONSTANT_Utf8

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Constant_Class

CONSTANT_Class_info{

U1 tag;

U2 name_index;

}

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CONSTANT_NameAndType

CONSTANT_NameAndType_info{

U1 tag;

U2 name_index;

U2 desciptor_index;

}

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CONSTANT_UTF8

CONSTANT_utf8_info{

U1 tag;

U2 length;

U2 bytes[length];

}

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Überblick

 Klassendatei ^

 Spezielle Strings ^

 Constant Pool ^

 Attribute

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Attribute



Code



ConstantValue



Deprecated



Exceptions



InnerClasses



LineNumberTable



LocalVariableTable



SourceFile



Synthetic

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ConstantValue

ConstantValue_attribute {

u2 attribute_name_index;

u4 attribute_length;

u2 constantvalue_index;

}

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Code

Code_attribute {

u2 attribute_name_index;

u4 attribute_length;

u2 max_stack;

u2 max_locals;

u4 code_length;

u1 code[code_ length]

u2 exception table_length;

{ u2 start_pc;

u2 end_pc;

u2 handler_pc;

u2 catch_type;

} exception_table[exception_table_length];

attribute_info attributes[attributes_count]:

}

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LocalVariableTable

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]:

}

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JAVA - KLASSENDATEIEN