Java platform

http://publicationslist.org/junio

The Java Platform

Prof. Dr. Jose Fernando Rodrigues Junior

Universidade de São PauloICMC-USP


Overview

• Introduction• Running Java• Evolution and Documentation• JDK and Compilation• Java vs C++• Coding• Conclusions


INTRODUCTION


Java Features• Modern project, eliminates known programming

pitfalls (like pointers and array overflow)

• Objected Oriented

• Powerful set of ready-to-go functionalities

• Rich documentation with Javadocs


Java Features

• Security: no memory overflow, sandbox (outworldlimited view), bytecode validation

• Performance: 50% to 100% C performance

• Wide scope of use: plenty of free code


Some facts• Released in 1995 - Sun Microsystems

• Java stands for nothing at all, it is only the brand of thecoffee its earlier programmers used to drink

• Style derived from C and C++, 99% OOP

• Code emulation: an old idea, inviable for long

• Initial Java appeal: applets over the Internet – it wasn’tgood for applications, bad performance and clumsy graphics

• Java main niches today: enterprise applications (multi-platform), middleware, database interfaces, cell phones andpda’s


Some facts


Java platform structure:4 components

1) Java runtime – Java Virtual Machine (JVM)2) Java language – 99.9% object oriented3) Java compiler – javac – and tools4) Java library – a lot of stuff ready-to-use

The term Java, can be rather confusing as“Java” might refer to any of these components


RUNNING JAVA


Running Java• Java is emulated in a virtual computer, the Java

Virtual Machine (JVM)

• The assembly language of JVM is the bytecode

• To run Java, one must have this computer– Physically: picoJava processor– Virtually: the Java Virtual Machine software

• Where to get this?– Install the Java Runtime Environment (JRE)

(also available as part of JDK)


Java Runtime Environment• What´s in JRE?

– JVM

– Java lib: some basic things are expected to bethere, check rt.jar (util, math, lang, awt, swing,etc)

– Runtime libraries: binaries, platform-specific


Java Execution• Java/Javaw: standard JVM evocation

• HotSpot: standard JVM, since Java 1.3, a lot faster

• Apache Harmony

• IBM J9

• Oracle JRockit

• Mac OS Runtime for Java


Java Execution

• All these JVM run bytecodes

• But bytecodes do not come only from Java:– JRuby: Rubby bytecode compiler– Jython : Python– JGNAT: Ada– JavaFX/Rhino: Java Script– Quercus: PHP– Clojure: Lisp– C2J: C


EVOLUTION AND DOCUMENTATION


Java Evolution

• 1995: Version 1.0, 8 packages with 212classes

• 1997: Version 1.1: 23 packages - 504classes, improved JVM, Swing is started

• 1999: Version 1.2 - Java 2 Platform - 59packages - 1520 classes, SDK, JFC (AWT,Swing and Java 2D)


Java Evolution• 2000: Version 1.3: 76 packages - 1842

classes, Hotspot JVM

• 2002: Version 1.4: 135 packages - 2991classes, better I/O and XML

• 2004: Version 5 (previously numbered 1.5) -165 packages, over 3000 classes, generics,faster startup, less memory


Java Evolution• 2006: Version 6, more on web, databases,

desktop-oriented API and security

• 2011: Java 7, structural redesign features;more modularization, multi-languageenhancements, developer productivity andperformance

• 2014: Java 8, functional programing,JavaScript runtime, among others


Java Evolution

Years

Pack

ages


Java Distributions

• Java Standard Edition (J2SE): client-sidestandalone applications or applets

• Java Enterprise Edition (J2EE): server-sideapplications such as Java servlets and JavaServerPages

• Java Micro Edition (J2ME): applications formobile devices such as cell phones


Main packages (libraries)• java.lang: metadata handlers (object, class, packages),

number classes, system,…• java.math• java.net• java.io• java.util• java.sql• java.applet• java.awt (inluding Java 2d), java swing• java.security• java.util: zip, jar, maps, sets, lists, vectors,…


Documentation

Demonstration


JDK AND COMPILATION


Java platform structure:4 components

The 4 components (runtime, compiler, language andlibraries) of the Java platform come in the softwarebundle known as Java Development Kit

Besides, the kit comes with:• javadoc: a framework for documentation• jar: a framework for archiving• jdb: a debugger• appletviewer: a platform for browser-designed

applications

And many, many other tools.


Java compilation• Javac: standard compiler

• Jikes (sourceforge): open source compiler, a lot faster

• GNU Compiler for Java (GCJ): part of gcc project,generates bytecodes or native code

• Eclipse Compiler for Java (ECJ): open source fromEclipse project

• Excelsior JET: commercial Java compilation (bytecodeand binary), optimization and distribution


Compilation vs Interpretation vs Emulation

• Compilation: the code is read and converted to themachine’s instruction set static binary executablefile later execution

• Interpretation: during execution, the code is readand, on the fly, actions are taken so as to have theexpected behavior script language (but not only)

• Emulation: the code is compiled to the instructionset of a machine different from the machine it is tobe executed on need of a machine emulator


Java Execution Framework• Java is compiled into bytecodes, the

instruction set of the Java Virtual Machine(JVM)

• Platform independence, over JVM emulation

• Just-in-time compilation, for performance

• Garbage collector: automated memorymanagement in JVM


Bytecodes• Bytecodes are quite simple and structured

• Different from binaries, it is not difficult to get abytecode file and reverse engineer it to the originalcode

• This fact has lead to the advent of obfuscation

• Obfuscation: obfuscator software shuffles bytecodesso that reverse engineering becomes a lot moredifficult and, eventually, useless


Not only from Sun• Provided by Sun (GNU Public License) and others:

– GNU Classpath– OpenJDK (da própria Sun)– OpenJDK-IcedTea (Red Hat)– Kaffe (http://www.kaffe.org/)– Kada, portable devices (http://www.kadasystems.com/)– LaTTe– Dinkum Jcore Library– Microsoft SDK– SableVM– IBM's J9 JDK– Oracle Corporation's JRockit– Blackdown Java (Linux JDK)– Apache Harmony


Why Java from other vendors?

• Open source software with an agreementlicense different from Sun´s

• Use other languages to have the benefitsof Java

• Better performance


Also Java• Servlets: Java used the same way as CGI

• JSP: JavaServer Pages, Java used thesame way as PHP and ASP

• Java FX: a higher level script languagethat runs on the JVM - Java FX competeswith Adobe Flash (Action Script)


Mobile Java• There is no, de facto, hardware platform for mobile

devices

• Hence, a multi-platform solution is a good choice

• One of the greatest Java niches is mobile

• Java Platform, Micro Edition (ME): the Javaplatform for embedded systems, mobile devicesand set-top boxes


Mobile Java• There is no, de facto, hardware platform for mobile

devices

• Hence, a multi-platform solution is a good choice

• One of the greatest Java niches is mobile

• Java Platform, Micro Edition (ME): the Javaplatform for embedded systems, mobile devicesand set-top boxes

There is an even smaller subset of the Java Platform, called Java Card

It provides Java in an enviroment with no more than the 16 KB found in smart cards


Java 7 - Platform


JAVA VS C++


Java vs C++


Java vs C++• Java Has No Pointers:

– referencing and dereferencing: it is handled for youautomatically

– no manipulation of pointers or memory addresses ofany kind:

• no pointer arithmetic• no computation of the size, in bytes, of any primitive type or object

• Why?– pointers are a source of bugs: no pointers simplifies the

language and eliminates many potential bugs– pointers and pointer arithmetic: they could be used to

sidestep Java's run-time checks and security mechanisms -no pointers allows Java to provide the security guaranteesthat it does


Java vs C++• Java Has No Global Variables: in case it is very needed, one has

to use static modifiers inside classes, attributes must be inside aclass

• Java Does Not Support Multiple Inheritance: multipleinheritance is not necessary, and it can be better accomplishedwith interfaces

• Java Does Not Allow Operator Overloading: it might permitextensions to the syntax of the language, which is not good

• No pre-compilation: that is, no .h, no #ifdefs, no defines and nomacros


Other features• Java has both kinds of comments like C++ does

• Everything must be in a class: no structs, enumerations norunions, only classes

• No headers: all method definitions are defined in the body ofthe classes

• Static quoted strings: they are automatically converted intoString objects

• Objects of non-primitive types can be created only via new:there’s no equivalent to creating non-primitive objects “on thestack” as in C++


Other features• All array accesses are checked for bounds violations

• Automatic garbage collection prevents memory leaks

• Clean, relatively fool-proof exception handling

• Simple language support for multi-threading

• Bytecode verification of network applets


CODING


Java IDEs - Gel


Java IDEs - NetBeans


Java IDEs - Eclipse


A Simple Java Program

import java.net.*;/*First Java program*/class SystemHello{public static void main(String args[]){try{System.out.println("Hi, my name is " + InetAddress.getLocalHost().getHostName() +" , my IP is " + InetAddress.getLocalHost().getHostAddress());

}catch(Exception e){System.out.println("Exception caught ="+e.getMessage());

}} //end main method} //end class


Using NotePad


Similar C/C++


Similar C/C++


Creating, Compiling, and Running Programs

Source Code

Compile Source Code i.e., javac Syste mHello.java

Bytecode

Run Byte odei.e., java SystemHe ll o

Re sult

If compilation errors

If runtime er rors o r incorrect result

impor t java.net.*; /*F ir s t Java pr ogram*/ class Sys temHell o{ public s tatic voi d mai n(Str ing ar gs[ ]){ tr y{ Sys tem.out.pri ntln( "Hi , my nam e i s " + InetAddress .get Local Host( ).getHo stName() + " , m y IP is " + InetAddress .getL ocalHost() .get HostAddress() ); }cat ch( Exception e){ Sys tem.out.pri ntln("E xception caught = "+ e.get Message()) ; } } //end main method } //end class

… Method Syste mHello() 0 aload_0 … Method void main(java.la ng.String[]) 0 getstatic #2 … 3 ldc #3 <S tring "Wel come to Java!"> 5 invokevirt ual #4 …

Saved on the disk

stored on the disk

Source code (d eveloped by the programmer)

Byte code (generated by the compiler for JVM to read an d interpret, not fo r you to unders tand)

Create/Modi fy Source Code


Compiling and Running Java from the Command prompt

• Set path to JDK bin directory– set path=c:\Program Files\java\ jdk1.6.0_16 \bin

• Compile– javac SystemHello.java

• Run– java SystemHello


Compiling and Running Java from NetBeans

• Install NetBeans

• Type code

• Run


Anatomy of a Java Program• Comments• Package• Reserved words• Modifiers• Statements• Blocks• Classes• Methods• The main method


Comments

• Comments are:– preceded by two slashes (//) in a line– enclosed between /* and */ in one or multiple lines


Package• The first line in the program specifies a package tobe imported• Here we import network functionalities


Reserved Words• Words that have a specific meaning to thecompiler and cannot be used for other purposes• For example, the word class• Other reserved words are public, static, void, tryand catch


Modifiers• Modifiers specify the properties of the data, methods,and classes and how they can be used

• Examples of modifiers are public and static• Other modifiers are private, final, abstract, andprotected


Statements• A statement represents an action or a sequence ofactions• System.out.println


Blocks

• A pair of braces in a program forms a block thatgroups components of a program


Classes• The class is the essential Java construct. A class is a template or blueprint for objects

• To program in Java, you must understand classes and be able to write and use them


Methods• Methods: a collection of statements that performsa sequence of operations for a specific task

• It can be used even without fully understanding thedetails of how it works


The main Method• Provides the control of program flow• JVM executes the application by invoking the mainmethod

public static void main(String args[]){

// Statements;

}

• Any/every class can have a public static mainmethod - so, every class is potentially executablegood for tests


The main Method• Provides the control of program flow• JVM executes the application by invoking the mainmethod

public static void main(String[] args) {

// Statements;

}


Modificadores de Acesso

Modificador Classe Pacote Sub-classe WorldPublic X X X XProtected X X X{nenhum} X XPrivate X


Tipos Primitivos

Tipo Tamanho Valor Mínimo Valor Máximo Valor Padrão

byte 8-bit signed -128 127 0

short 16-bit signed -32,768 32,767 0

int 32-bit signed -2,147,483,648 2,147,483,647 0

long 64-bit signed -9,223,372,036,854,775,808 9,223,372,036,854,775,807 0

float 32-bit IEEE -1.4023984e-45 3.40282347e+38 0.0

double 64-bit IEEE -4.94065645841246533e-324 1.79769313486231570e+308 0.0

boolean - false true false

char 16-bit Unicode \u0000 \uffff \u0000

Fonte: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/datatypes.html


OperadoresOperador Significado

= Atribuição+ Adição e concatenação de Strings- Subtração, operador unário para inverter um número* Multiplicação/ Divisão

% Resto da divisão++ Incremento-- Decremento! Complemento, inverte um valor booleano

== Igual a!= Diferente de> Maior que>= Maior ou igual a< Menor que<= Menor ou igual a


OperadoresOperador Significado

&& Condicional E (AND)|| Condicional OU (OR)?: Ternário (if-then-else)new Instancia um objeto

instanceof Compara um objeto a um determinado tipo~ Operador binário de complemento

<< Signed left shift (deslocamento bit-a-bit para a esquerda)>> Signed right shift (deslocamento bit-a-bit para a direita)

>>> Unsigned right shift& Operador E binário^ Operador OU exclusivo binário| Operador OU inclusivo binário

Fonte: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/operators.html


Precedência de Operadores

Fonte: http://tecnoesis.wordpress.com/2009/11/07/declaring-initializing-and-using-variables/


Palavras Reservadas

abstract continue for new switchassert*** default goto* package synchronizedboolean do if private thisbreak double implements protected throwbyte else import public throwscase enum**** instanceof return transientcatch extends int short trychar final interface static voidclass finally long strictfp** volatileconst* float native super while

* Não utilizado** Adicionado na versão 1.2

*** Adicionado na versão 1.4**** Adicionado na versão 5.0

Fonte: http://docs.oracle.com/javase/tutorial/java/nutsandbolts/_keywords.html


Conclusion

• Java gathers two of the most importantand useful things in computing:

– organization

– simplicity

Technology

Java platform