20030425 - JavaVirtualMachine&ClassFile

8/7/2019 20030425 - JavaVirtualMachine&ClassFile

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Java Virtual MachineJava Virtual Machine


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Java: Not a Traditional Programming LanguageJava: Not a Traditional Programming Language

Hardware

Win32/NTLinux Solaris

Java Platform

Java

Source

(*.java)Java Compiler

Java

Bytecode

(*.class)

Java bytecode

(moves locally or via web)


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Java PlatformJava Platform


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Java Platform & VM & DevicesJava Platform & VM & Devices


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Java 2 XXX EditionJava 2 XXX Edition

Each edition is a developer treasure chest ofEach edition is a developer treasure chest oftools and supplies that can be used with atools and supplies that can be used with aparticular product:particular product: Java virtual machines that fit inside the range ofJava virtual machines that fit inside the range of

consumer devicesconsumer devices a library of APIs that are specialized for each type ofa library of APIs that are specialized for each type of

devicedevice tools for deployment and device configurationtools for deployment and device configuration a profile, that is, a specification of the minimum set ofa profile, that is, a specification of the minimum set ofAPIs useful for a particular kind of consumer deviceAPIs useful for a particular kind of consumer device(set(set--top, screenphone, wireless, car, and digitaltop, screenphone, wireless, car, and digitalassistant) and a specification of the Java virtualassistant) and a specification of the Java virtualmachine functions required to support those APIsmachine functions required to support those APIs


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Java 2 Standard EditionJava 2 Standard Edition


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Java 2 Enterprise EditionJava 2 Enterprise Edition


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Various VMVarious VM

JVM (J2EE & J2SE)JVM (J2EE & J2SE) WellWell--known Java Virtual Machine.known Java Virtual Machine.

CVM, KVM (J2ME)CVM, KVM (J2ME)Addresses on vast small devices.Addresses on vast small devices.

Reduces some VM features to fit resourceReduces some VM features to fit resource--constrained devices.constrained devices.

JCVM (Java Card)JCVM (Java Card)Addresses on smart cards.Addresses on smart cards.

It has least VM features.It has least VM features.


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J2ME : ConfigurationJ2ME : Configuration

J2ME technology has two design centersJ2ME technology has two design centers----things that you hold in your hand andthings that you hold in your hand and

things you plug into a wall.things you plug into a wall.

Configurations are composed of the twoConfigurations are composed of the twolowlow--level APIs and optimized virtuallevel APIs and optimized virtualmachines .machines .


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J2ME : ProfileJ2ME : Profile

A profile is a specification that details theA profile is a specification that details theJava technology APIs, built on top of andJava technology APIs, built on top of andutilizing the underlying Configuration.utilizing the underlying Configuration.

Profiles specify both APIs and theProfiles specify both APIs and theConfiguration.Configuration.


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Profiles:Foundation & MIDPProfiles:Foundation & MIDP

MIDP:Mobile Information Device ProfileMIDP:Mobile Information Device Profile

Foundation is a set of JavaTM APIs which,Foundation is a set of JavaTM APIs which,

together with the Connected Devicetogether with the Connected DeviceConfiguration (CDC).Configuration (CDC).

MIDP is a set of Java APIs which, togetherMIDP is a set of Java APIs which, togetherwith the Connected Limited Devicewith the Connected Limited DeviceConfiguration (CLDC).Configuration (CLDC).


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CVM & CDC (1)CVM & CDC (1)

CDC : Connected Device ConfigurationCDC : Connected Device Configuration

CVM is a Java 2 virtual machine designed forCVM is a Java 2 virtual machine designed fordevices needing the functionality of the Java 2devices needing the functionality of the Java 2

virtual machine feature set, but with a smallervirtual machine feature set, but with a smallerfootprint.footprint.

The Connected Device Configuration (CDC)The Connected Device Configuration (CDC)

includes the CVM and basic class libraries toincludes the CVM and basic class libraries tosupport Java language applications on consumersupport Java language applications on consumerelectronic and embedded devices.electronic and embedded devices.


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CVM & CDC (2)CVM & CDC (2)

CDC is designed for the devices such asCDC is designed for the devices such assmart communicators, pagers, personalsmart communicators, pagers, personaldigital assistants (PDAs), and interactive,digital assistants (PDAs), and interactive,digital television setdigital television set--top boxes.top boxes.

Typically, these devices run a 32Typically, these devices run a 32--bitbitmicroprocessor/controller and have moremicroprocessor/controller and have morethan 2.0MB of total memory.than 2.0MB of total memory.


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KVM & CLDC (1)KVM & CLDC (1)

CLDC : Connected Limited Device ConfigurationCLDC : Connected Limited Device Configuration

K virtual machine (KVM) is a new, highlyK virtual machine (KVM) is a new, highlyoptimized Java virtual machine specificallyoptimized Java virtual machine specifically

designed for resourcedesigned for resource--constrained consumerconstrained consumerdevices.devices.

CLDC outlines the most basic set of libraries andCLDC outlines the most basic set of libraries andJavaTM virtual machine features that must beJavaTM virtual machine features that must be

present in each implementation of a Java 2present in each implementation of a Java 2Platform, Micro Edition environment on highlyPlatform, Micro Edition environment on highlyconstrained devices.constrained devices.


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JCVM (1)JCVM (1)


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JCVM (2)JCVM (2)


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JCVM (3)JCVM (3)

JCVM has least VM features defined inJCVM has least VM features defined inJVM SPEC.JVM SPEC.

Unsupported Features:Unsupported Features: Dynamic Class LoadingDynamic Class Loading

Security ManagerSecurity Manager

Garbage Collection & FinalizationGarbage Collection & Finalization

ThreadsThreads

CloningCloning


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JCVM (4)JCVM (4)

Unsupported Keywords:Unsupported Keywords:

nativenative

synchronizedsynchronized transienttransient

volatilevolatile

Unsupported Types:Unsupported Types:

char, float, double, longchar, float, double, long

Arrays that is more than one dimension.Arrays that is more than one dimension.


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JCVM (5)JCVM (5)

In general, none of Java core API classesIn general, none of Java core API classesare supported in the Java Card platform.are supported in the Java Card platform.

Some classes from java.lang package areSome classes from java.lang package aresupported, but none of the rest are.supported, but none of the rest are.

Class java.lang.System is not supported.Class java.lang.System is not supported.Instead, it supplies a classInstead, it supplies a class

javacard.framework.JCSystem, whichjavacard.framework.JCSystem, whichprovides an interface to system behavior.provides an interface to system behavior.


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VM MechanismVM Mechanism


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Internal Architecture of JVMInternal Architecture of JVMJava Runtime System

Operating System

native method

Java Class

Library

Java bytecode

(*.class)

execution engine

Exception,

Thread,

Security.

Heap

Class Loader& Verifier

nativemethod linker

classmethod

area

nativemethodarea

Java Stack,

Register


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Method Area & HeapMethod Area & Heap

Each JVM implementation has a heap andEach JVM implementation has a heap anda method area.a method area.

Heap is shared among all threads. It is theHeap is shared among all threads. It is theruntime data area from which for all classruntime data area from which for all classinstances and arrays is allocated.instances and arrays is allocated.

Method area is shared among all threads.Method area is shared among all threads.

It stores perIt stores per--class structures such as theclass structures such as theruntime constant pool, field and methodruntime constant pool, field and methoddata, the code for methods.data, the code for methods.


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Class Loader & VerifierClass Loader & Verifier

Loading: Load binary representation of classLoading: Load binary representation of class(*.class).(*.class).

Linking:Linking: Verification: Ensure that the binary representation isVerification: Ensure that the binary representation is

structurally valid.structurally valid. Preparation: Create the static fields for the class orPreparation: Create the static fields for the class or

interface and initializing those fields to their standardinterface and initializing those fields to their standarddefault values.default values.

Resolution: Determine concrete values from symbolicResolution: Determine concrete values from symbolic

references in the runtime constant pool .references in the runtime constant pool . Initializing: Invoke its static initializers and theInitializing: Invoke its static initializers and the

initializers for static fields declared in class.initializers for static fields declared in class.


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RegisterRegister

PC (program counter) register. It containsPC (program counter) register. It containsthe address of the Java virtual machinethe address of the Java virtual machineinstruction currently being executed.instruction currently being executed.

Each thread has its own PC register.Each thread has its own PC register.

If the method currently being executed byIf the method currently being executed bythe thread is native, the value of the Javathe thread is native, the value of the Javavirtual machine's pc register is undefined.virtual machine's pc register is undefined.


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Java StackJava Stack

Java Stack stores frames.Java Stack stores frames.

Each thread has a private JVM stack,Each thread has a private JVM stack,

created at the same time as thread.created at the same time as thread. Java Stack holds local variables and partialJava Stack holds local variables and partial

results, and plays a part in methodresults, and plays a part in methodinvocation and return.invocation and return.


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Java Stack : frame (1)Java Stack : frame (1)

A new frame is created each time aA new frame is created each time amethod is invoked. A frame is destroyedmethod is invoked. A frame is destroyedwhen its method invocation completes.when its method invocation completes.

A frame is used to store data and partialA frame is used to store data and partialresults, as well as to perform dynamicresults, as well as to perform dynamiclinking, return values for methods, andlinking, return values for methods, and

dispatch exception.dispatch exception.


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Each frame has its own array of localEach frame has its own array of localvariables, its own operand stack, and avariables, its own operand stack, and areference to the runtime constant pool ofreference to the runtime constant pool ofthe class of the current method.the class of the current method.

local variables

Java Stack

operand stack

othersframe


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class LocalVariableExample {

public static void runClassMethod(int i, long l, float f) { }

public void runInstanceMethod(char c, double d, boolean b) { }

}

runClassMethod()

int i

long l

float f

0

1

3

runInstanceMethod()

double d

char c

boolean b

0

2

4

1

reference


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iload_0

iload_1

iadd

istore_2

98

0

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98

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local variables

operand stack


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class pointerclass pointer

previous frame pointerprevious frame pointer

exception tableexception table


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Execution Engine (1)Execution Engine (1)

A virtual processorA virtual processor ---- the core of JVM.the core of JVM.

Programming aspect : interpreter.Programming aspect : interpreter.

Read bytecode stream then execute theRead bytecode stream then execute theinstructions.instructions.

The performance can be improved byThe performance can be improved by

JustJust--InIn--Time(JIT) compiler.Time(JIT) compiler.


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Execution Engine (2)Execution Engine (2)

int y=x+5;

iload 1

bipush 5

iadd

istore 2

iload 1 bipush 5 iadd istore 2

21 1 16 5 96 54 2


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JavaJava

Assembly LanguageAssembly Language


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Count.javaCount.javapublic class Count

{

public static void main(String[] args)

{

int i;

for(i=0;i


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Count.j (1)Count.j (1).class public Count.super java/lang/Object

.method public ()V

aload_0

invokespecial java/lang/Object/()Vreturn

.end method


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Count.j (2)Count.j (2)

.method public static main([Ljava/lang/String;)V

.limit stack 3

.limit locals 4

getstatic java/lang/System/out Ljava/io/PrintStream;

astore_1

bipush 10

istore_2


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Count.j (3)Count.j (3)

Loop:bipush 10iload_2isubinvokestatic java/lang/String/valueOf(I)Ljava/lang/String;

astore_3aload_1aload_3invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

iinc 2 -1

iload_2ifne Loop

return.end method


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Java AssemblerJava Assembler

Not an official assembler. There is noNot an official assembler. There is nostandard for java assembly language.standard for java assembly language.

http://mrl.nyu.edu/~meyer/jasmin/http://mrl.nyu.edu/~meyer/jasmin/


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Class File StructureClass File Structure


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Tables of Class FileTables of Class File

Top Table:Top Table: Basic information of the whole class.Basic information of the whole class.

Constant Pool Table:Constant Pool Table: Records string, constant, reference, method name, field nameRecords string, constant, reference, method name, field name

Interface Table:Interface Table: What interface are implemented by this class.What interface are implemented by this class.

Field Table:Field Table: The fields which class owns.The fields which class owns.

Method Table:Method Table: The methods which class owns.The methods which class owns.

Attribute Table:Attribute Table: The extra information of class, field, methodThe extra information of class, field, method and so on.and so on.


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Magic NumberMagic Number

0xCA, 0xFE, 0xBA, 0xBE0xCA, 0xFE, 0xBA, 0xBE

Every class file contains these 4Every class file contains these 4--byte databyte datain the header.in the header.


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Type Descriptor (1)Type Descriptor (1)

Primitive Type:Primitive Type: B : byteB : byte

C : charC : char

D : doubleD : double F : floatF : float

I : intI : int

J : longJ : long S : shortS : short

Z : booleanZ : boolean


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Class Type:Class Type:

L;L;

Ex1: Ljava/lang/String;Ex1: Ljava/lang/String;

Ex2:Ex2: Ljava/io/PrintStream;


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Array Type:Array Type:

[[

Ex1: [CEx1: [C char[]char[]

Ex2: [[FEx2: [[F float[][]float[][]

Ex3: [Ljava/lang/Thread;Ex3: [Ljava/lang/Thread; Thread[]Thread[]


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Method:Method: ()()

VV indicatesindicates voidvoid (used in return type)(used in return type)

Ex1: ()VEx1: ()V void xyz() {void xyz() {}}

Ex2: (SF[Ljava/lang/Thread;)IEx2: (SF[Ljava/lang/Thread;)I int xyz(short x, float y, Thread[] z) {int xyz(short x, float y, Thread[] z) {}}


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Constant PoolConstant Pool

TagTag ValueValue DescriptionDescription

CONSTANT_Utf8CONSTANT_Utf8 11 array of bytearray of byte

CONSTANT_IntegerCONSTANT_Integer 33 integerinteger

CONSTANT_FloatCONSTANT_Float 44 float float

CONSTANT_LongCONSTANT_Long 55 longlong

CONSTANT_DoubleCONSTANT_Double 66 DoubleDouble

CONSTANT_ClassCONSTANT_Class 77 TagTag--1 index1 index

CONSTANT_StringCONSTANT_String 88 TagTag--1 index1 index

CONSTANT_FieldrefCONSTANT_Fieldref 99 TagTag--7 index + Tag7 index + Tag--12 index12 index

CONSTANT_MethodrefCONSTANT_Methodref 1010 TagTag--7 index + Tag7 index + Tag--12 index12 index

CONSTANT_InterfaceMethodrefCONSTANT_InterfaceMethodref 1111 TagTag--7 index + Tag7 index + Tag--12 index12 index

CONSTANT_NameAndTypeCONSTANT_NameAndType 1212 TagTag--1 index(filed,method name)1 index(filed,method name)

+ Tag+ Tag--1 index(type descriptor)1 index(type descriptor)


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Access FlagAccess Flag

FlagFlag ValueValue

ACC_PUBLICACC_PUBLIC 0x00010x0001

ACC_PRIVATEACC_PRIVATE 0x00020x0002

ACC_PROTECTEDACC_PROTECTED 0x00040x0004

ACC_STATICACC_STATIC 0x00080x0008

ACC_FINALACC_FINAL 0x00100x0010

ACC_SUPERACC_SUPER 0x00200x0020

ACC_SYNCHRONIZEDACC_SYNCHRONIZED 0x00200x0020

ACC_VOLATILEACC_VOLATILE 0x00400x0040ACC_TRANSIENTACC_TRANSIENT 0x00800x0080

ACC_NATIVEACC_NATIVE 0x01000x0100

ACC_INTERFACEACC_INTERFACE 0x02000x0200

ACC_ABSTRACTACC_ABSTRACT 0x04000x0400


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out.jout.j.class public out

.super java/lang/Object

.method public ()V

aload_0

invokespecial java/lang/Object/()V

return

.end method

.method public static main([Ljava/lang/String;)V

.limit stack 2

getstatic java/lang/System/out Ljava/io/PrintStream;ldc Hello World

invokevirtual java/io/PrintStream/println(Ljava/lang/String;)V

return

.end method


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publicpublic[ ][ ] [ ] [ ]

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stack sizestack size

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local variable sizelocal variable size

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bytecode lengthbytecode length

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bytecode contentbytecode content

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exception sizeexception size

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extra attribute numberextra attribute number

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public + staticpublic + static

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method namemethod name

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method typemethod type

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attribute typeattribute type

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method lengthmethod length

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stack sizestack size

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local variable sizelocal variable size

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bytecode lengthbytecode length

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bytecode contentbytecode content

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exception sizeexception size

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extra attribute numberextra attribute number

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atttribute numberatttribute number

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attribute typeattribute type

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attribute lengthattribute length

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attribute dataattribute data

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The EndThe End

Documents

20030425 - JavaVirtualMachine&ClassFile