snu ee shin jin woo

SNU EE

Shin Jin Woo

The Java Virtual Machine(Design & APIs)

2005. 10. 19

http://java.sun.com/

Java Virtual MachineJava Virtual Machine22

1. What is JVM?

2. Terminologies

3. The Java Class Files

4. Data Types in JVM

5. Runtime Data Area

6. Java Instruction Set

7. Verification of Class Files

8. Java APIs

Table of Contents


1. What is a Java Virtual Machine?

Module 1

• an abstract computing machine

Java Virtual Machine

• own instruction set(Java ISA) • memory manipulation at runtime

classloader

executionengine

Host OS

The Java API’s class file

user class files

JVM

bytecodes

native method invocation


2. Terminologies

JRE(Java Runtime Environment)

• : contains the Java virtual machine, classes comprising the Java 2 Platform API, and supporting files

JDK(Java Development Kit)

• : JRE, Development Tools(compiler, debugger), additional library

compile-time environment run-time environment

a.java b.java c.java

a.class b.class c.class

a.class b.class c.class

Object.class String.class

Javacompiler JVM


3. What is a Class File?

Java Class Files- precisely defined binary file format for Java

programs- put only one class or interface in a single class

file- primary vehicle for delivering program to JVM

Java LanguageProgram

C LanguageProgram

Compiler

Compiler

Java Class File

Java Class File


3. What is a Class File?

What is in Class Files

Magic NumberVersion InformationConstant Pool size

Constant PoolAccess Flags

This ClassSuper Class

0xCAFEBABE, 4byte

Interface CountInterfaces

Field CountField Information

Method CountMethods

Attributes CountAttributes


4. Data Type in JVM

- int - char- byte- short- float- double- returnAddress : used by subroutine mechanism

jsr places return address on operand stack

Primitive Data Types

Reference Data Types

- reference : points to an object stored in memory


5. Runtime Data Areas

PC Registers

: each JVM thread has its own program counter: the index in bytecode of the instruction

Java Virtual Machine Stacks: each JVM thread has its own stacks: invoke method -> new frame is allocated on

stack: store operand stack, local variables, state

variables

Thread 1

Thread 2

foo()

draw()

boo()Local VariablesOperand Stacks

Local VariablesOperand Stacks

Local VariablesOperand Stacks



The Operand Stack

- used to pass arguments- receive return results- interpreter is responsible for transferring

return result to the caller operand stack

Local Variables

- number of local variables in stack is determined at compile time- local variables are numbered ex) dconst_0 dstore 1



Heap

- one heap per one JVM- created on VM start-up- all class instance and arrays are allocated in heap- objects are never deallocated

Method Area

- one M.A for one JVM- created on VM start-up- analogous to ‘text’ segment- stores constant pool, field and method data, code

for method


Constant Pool

- analogous to ‘symbol table’- a collection of all symbolic data need by a class- each constant pool is private to its class


:5: add g0, FSIZE(class)+GC_HEAD, it06: call 07: sethi %hi(class->dtable), rt28: or r3, rt2, %lo(class->itable)

:


6. Java Instruction Sets

Java Instruction Sets

- opcode is just one byte (256 combination possible) - additional index bytes- additional date bytes

opcode

opcode index1 index2

opcode date



Data Movement Instructions

1. stack manipulation instructions iconst_1, bipush, pop, dup, swap

ex) bipush 10 bipush 20 swap pop dup pop2

10

20

20

10

20 20

20



Type Conversion

- convert one type of item on the stack to another ex) i2f, i2d, i2l, f2i, f2l…

Functional Instructions

- operands are always taken from the stack and results are placed on the stack

ex) iadd, iand

Control Flow Instructions

- conditional branches ex) ifeq, if_icmpeq- unconditional branches ex) jsr, ret returnAddress type used


7. Verification of Class Files

Module 1

pass 1 – ensure that the file has the basic format of a class file

Verification of Class Files

It is done at Linking Time

pass 2 – verification without looking at actual codepass 3 – verifier checks the code array -> operand

stack tracking


8. Java APIs

Java Platforms

- J2SE, J2EE, J2ME

Java APIs

java.lang

: core API package : have Obejct class

java.awt

: contains classes for constructing GUIs

java.io

: manage data stream, file I/O


8. Java APIs

Serialization & Reflection

- Serialization : make a implementation independent form of objects

In Java implement Serializable interface to do this

- Reflection : find all of objects members

network

storage

platform 1 platform 2

platformindependent

form

snu ee shin jin woo

Documents