itectural analays

8/11/2019 itectural analays

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Introduction to Sun Microsystems java

High level OOPL

Platform Independent

Case Sensitive


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Can you make coffee with it?


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It was meant to!!

A programming language for appliances!


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Java Virtual Machine

Must Run on Any Architecture

Program

in JavaJava

Compiler

Java

Bytecode

Java Virtual Machine

WRITE ONCE, RUN ANYWHERE!debug

pretty portable


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Doesnt Make Coffee Yet


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So Whats Java Good For?

Web applications!

Java Applet

Server

Java Applet


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Java on the Web: Java Applets

Clients download applets via Web browser

Browser runs applet in a Java Virtual Machine (JVM)

Interactive web, security, and client consistencySlow to download, inconsistent VMs (besides, flash

won this war)

Applet

ClientServer


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Java on the Web: J2EE

Thin clients (minimize download)

Java all server side

THIS IS WHAT YOULL BE DOING!!

ClientServer

JSPs

Servlets

EJB

JDBC


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The Java programming environment

Compared to C++:

no header files, macros, pointers and references, unions, operatoroverloading, templates, etc.

Object-orientation: Classes + Inheritance

Distributed: RMI, Servlet, Distributed object programming.

Robust: Strong typing + no pointer + garbage collection

Secure: Type-safety + access control

Architecture neutral: architecture neutral representation

Portable

Interpreted

High performance through Just in time compilation (compilerconverts byte code to native code) + runtime modification of code

Multi-threaded


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Java Features

Well defined primitive data types: int, float, double, char, etc.

int 4 bytes [2,147,648, 2,147,483,647] Control statements similar to C++: if-then-else, switch, while, for

Interfaces

Exceptions

Concurrency (Multi-Threading)

Packages

Reflection (makes it possible to inspect classes, interfaces, fields and

methods at runtime, without knowing the names of the classes,

methods etc. at compile time. It is also possible to instantiate new

objects, invoke methods and get/set field values using reflection. )

Applet model


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The Java programming environment

Java programming language specification

Syntax of Java programs Defines different constructs

Java byte code: Intermediate representation for Java programs

Java compiler: Program that Transform Java programs into Java

byte code

Java interpreter: Read programs written in Java byte code andexecute them (converts byte into native code. i.e Codes other

than java).

Java virtual machine: The whole technology is based on the

concept of JVM. Translator of byte code into platform specific

machine language. It is the Runtime system that providesvarious services to running programs (Logical representation of

JRE)


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JVM


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JIT (Just-in-Time) Compilation


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JVM

JVM stands for Java Virtual Machine. Itsan abstract computer

or virtual computer which runs the compiled java programs.Actually JVM is a software implementation which stands on the

top of the real hardware platform and operating system. It

provides abstraction between the compiled java program and

the hardware and operating system.

JIT: This Compiler converts byte code to native code.

Old Interpreter was replaced with JIT to increase the

performance of java applications.

When JVM compiles the class file it does not compile the full

class file in one shot. Compilation is done on function basis or

file basis. Depending on need basis the compilation is done.This type of compilation is termed as JIT or Just-in- Time

compilation.


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General ( java1.5Tiger & java1.6Mustang (wild horse))

can run your compiled code on any operating system without

recompiling your source code JVM and Java Application Programming Interface (API) that are

kinds of readymade software components

Java programming environment: Set of libraries that provide

services such as GUI, data structures,etc.

Java enabled browsers: Browsers that include a JVM + ability toload programs from remote hosts

Platform Dependent JVM, Java Compiler, Java Interpreter, C

program, JDK.

Platform IndependentJava program.

JDK (Java Development Kit) Collection of various tools,required to develop and run program

Tools ( JRE, Java Compiler, Java Interpreter)


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Path & classpath

To run the program , Set the properties, then only MS-DOS

knows about java commands. (Temporary) set path=%path%; (jdk - bin) (Binary files will be accessible in all

the folders & driver of OS)

set classpath=%classpath%.; (jdk - lib) (The class will be

available in all the folder of OS)

The other way of setting up the path My Computer Advanced Environment variables proceed.

(Permanent)

JAVA_HOMEjdk

Importance of path: Binary will be accessible in all the folders

and driver of O.S

Importance of classpath: .class files will be available in all the

folders of O.S


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OOPs Concepts- PIE

Abstraction: Providing essential properties and

operation of an object by hiding internal things. Encapsulation: Placing all the properties and

operations of an object in one place.

The place is called as class, Properties are called as

variables, Operations are called as methods. Polymorphism : Remote control application - one

button is used for switch on/ off.


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How are Java programs written?

Define a class HelloWorld and store it into a file:

HelloWorld.java:public class HelloWorld {

public static void main (String[] args) {

System.out.println(Hello, World);

}

}

Compile HelloWorld.javajavac HelloWorld.java

Output: HelloWorld.class

Runjava HelloWorld

Output: Hello, World


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How are variables declared?

Fibonacci:

class Fibonacci {public static void main(String[] arg) {

int lo = 1;

int hi = 1;

System.out.println(lo);

while (hi < 50) {

System.out.println(hi);

hi = hi + lo;

lo = hi lo;

}}

}


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How to define expressions?

Arithmetic: +, -, *,/, %, =

8 + 3 * 2 /4

Use standard precedence and associativity rules

Predicates: ==, !=, >, =,


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How are simple methods defined?

Every method is defined inside a Java class definition

public class Movie {public static int movieRating(int s, int a, int d) {return s+a+d;

}

}

public class Demo {

public static void main (String argv[]) {

int script = 6, acting = 9, directing = 8;

displayRating(script, acting, directing);

}

public static void displayRating(int s, int a, int d){

System.out.print(The rating of this movie is);

System.out.println(Movie.movieRating(s, a, d));

}

}


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How are control structures specified?

Typical flow of control statements: if-then-else, while, switch, do-while, and blocksclass ImprovedFibo {

static final int MAX_INDEX = 10;

public static void main (String[] args) {

int lo = 1;

int hi = 1;

String mark = null;for (int i = 2; i < MAX_INDEX; i++) {

if ((i % 2) == 0)

mark = " *";

else mark = "";

System.out.println(i+ ": " + hi + mark);hi = lo + hi;

lo = hi - lo;

}}}


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What are classes and objects?

Classes: templates for constructing instances

Fields

Instance variables

Static variables

Methods

Instance

Static

class Point {

public double x, y;

}

Point lowerleft = new Point();

Point upperRight = new Point();

Point middlePoint = new Point();

lowerLeft.x = 0.0; lowerLeft.y = 0.0;

upperRight.x = 1280.0; upperRight.y = 1024.0

middlePoint.x = 640.0; middlePoint.y = 512.0


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How are instance methods defined?

Instance methods take an implicit parameter: instance

on which method is invokedpublic class Movie {public int script, acting, directing;

public int rating() {return script + acting + directing;

}

}

public class Demo {public static void main (String argv[]) {

Movie m = new Movie();

m.script = 6; m.acting = 9; m.directing = 8;

System.out.print(The rating of this movie is);System.out.println(m.rating());

}

}


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How to extend classes?

Inheritance: mechanism for extending behavior of

classes; leads to construction of hierarchy of classes[Note: no multiple inheritance]

What happens when class C extends class D:

Inherits instance variables

Inherits static variables Inherits instance methods

Inherits static methods

C can:

Add new instance variables

Add new methods (static and dynamic)

Modify methods (only implementation)

Cannot delete anything


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How to extend classes?

public class Attraction {public int minutes;public Attraction() {minutes = 75;}public int getMinutes() {return minutes;}public void setMinutes(int d) {minutes = d;}

}public class Movie extends Attraction {

public int script, acting, directing;public Movie() {script = 5; acting = 5; directing = 5;}public Movie(int s, int a, int d) {

script = s; acting = a; directing = d;}public int rating() {return script + acting + directing;}

}public class Symphony extends Attraction {

public int playing, music, conducting;public Symphony() {playing = music = conducting = 5;}public Symphony(int p, int m, int c) {

playing = p; music = m; conducting = c;}public int rating() {return playing + music + conducting;}

}


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What are abstract classes?

Abstract class: Merely a place holder for class

definitions; cannot be used to create instances.;public abstract class Attraction {

public int minutes;public Attraction() {minutes = 75;}public int getMinutes() {return minutes;}public void setMinutes(int d) {minutes = d;}public abstract void m();

}

Following is an error:Attraction x;x = new Attraction();

Following is not an error:

public class Movie extends Attraction { }public class Symphony extends Attraction { }Attraction x;x = new Movie ();x = new Symphony();


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Packages

Object

Attraction Auxiliaries Demonstration

Movie Symphony

extends

extends

How do we organize above classes into a single unit? Put them in file?

However, only one public class per file (whose name is same as files)

Solution: Place several files (compilation units) into a package


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Packagescontd.

units of organizing related Classes, Interfaces, Sub

packages Why?

Reduce name clashing

Limit visibility of names

Java programs typically organized in terms ofpackages and subpackages

Each package may then be divided into several packages,

subpackages, and classes

Each class can then be stored in a separate file

Each source file starts with something like:package mypackage;

Code in source file is now part ofmypackage


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Packagescontd.

package onto.java.entertainment;public class Movie extends class Attraction {}

package onto.java.entertainment;import java.io.*;import java.util.*;

public class Auxiliaries { }

package onto.java.entertainment;public abstract class Attraction { }

Where to store packages?

How does Java find packages?

Export and Import

Access control


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Exceptions

public class A {public void foo() throws MyException {

if(aBadThingHappened()) {throw new MyException();}

}public void bar() {

try {this.foo();

} catch (MyException e) {e.printStackTrace();

}}

}

public class MyException extends Exception {public MyException() {}

public MyException(String message) {super(String message);

}}


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Finally

public class A {public void foo() throws MyException {

throw new MyException();}

}public void bar() {

try {this.foo();

} catch (MyException e) {e.printStackTrace();

} catch (YourException e) {e.printStackTrace();

} finally {... // always executed before leaving the try/catch

}

}}


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Resources

http://java.sun.com/

Java[tm] 2 Platform, Standard Edition v1.4.1

java, javac, jar, jre, etc.

Any platform... FREE!

Online documentation and tutorials

http://www.eclipse.org/

Integrated development environment (IDE) for nothing in particular Java[tm] development tools (JDT) (comes with Eclips)

Project management

Editor

Incremental compiler

CVS support

C/C++ extension in progress

AspectJ support

Windows, Linux, and Mac.... FREE!
http://java.sun.com/http://www.eclipse.org/http://www.eclipse.org/http://java.sun.com/


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Qualifiers

publicany class* may access

(no qualifier) package protected only the class*and classes* in the same package may access

protectedonly the class* and decendent classes*

may access

privateonly the class* may access

The class or instances of the class (an object of the class)


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Package Protectedpackage edu.ucdavis;public class A {

int x;

}package edu.ucdavis;public class B {

void foo(A a) { a.x; } // OK, same package}

package edu.ucdavis.cs;public class B {

void foo(A a) { a.x; } // Not OK, different package}

package edu;public class B {


package edu.ucdavis.cs;public class B {


package org.omg;public class B {



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Threads

Multiple threads of execution within the same

program, share the same memory space ->lightweight.

Perform multiple tasks at the same time.

Work on the same task in parallel.

Heavily used in user interfaces. Web browsers: load web pages while the user can still scroll,

go back, open a new window, etc.

Web servers: serve multiple requests in parallel.

Can take advantage of multiple processors.

Threads in Java Java manages and schedules threads

Java provides synchronize to help coordinate multiplethreads

C


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Creating a Thread in Java

public class MyThread extends Thread {public MyThread(String threadName) {

super(threadName);}public void run() {

for(int i = 0; i < 10; i++) {System.out.println(i + + getName());try {

sleep((long)(Math.random() * 1000));

} catch(InterruptedException e) {}}

}}

C i Th d i J


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Creating a Thread in Java

public class ThreadTest {public static void main(String[] args) {

for(int i = 0; i < args.length; i++) {MyThread t = new MyThread(args[i]);t.start();

}}

}

> java ThreadTest Bob Frank0 Bob0 Frank1 Bob2 Bob1 Frank

3 Bob2 Frank3 Frank4 Frank...

C ti Th d i J i I t f


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Creating a Thread in Java via Interface

public class MyRunnable implements Runnable {String name;public MyRunnable(String name) {

this.name = name;}public void run() {

for(int i; i < 10; i++) {System.out.println(i + + name());try {sleep((long)(Math.random() * 1000));

} catch(InterruptedException e) {}}

}}

public class ThreadTest {public static void main(String[] args) {

for(int i = 0; i < args.length; i++) {Thread t = new Thread(new MyRunnable(args[i]), args[i]);t.start();

}}

}

P d C P bl


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Producer Consumer Problem

public class Producerextends Thread {private Share shared;

public Producer(Share s) {shared = s;

}

public void run() {for(int i = 0; i < 10; i++){

shared.put(i);}

}}

shared.put(0)

shared.get() // 0 gotten

shared.get() // 0 gotten again!!

shared.put(0)

shared.put(1)

shared.get() // 0 never gotten!!

public class Consumerextends Thread {private Share shared;

public Consumer(Share s) {shared = s;

}

public void run() {int value;

for(int i = 0; i < 10; i++) {value = shared.get();

}}

}

// what about simultaneous// access?!shared.put(0) shared.get()

RACE CONDITIONS!

S h i d


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public class Share {private int s;

public synchronized int get() { ... }public synchronized void put(int s) { ... }}

Synchronized

Synchronized provides mutual exclusion on an object For any object, only one thread may execute inside

any of that objects synchronized methods

Share s1 = new Share();Share s2 = new Share();

Thread t1 = ...;Thread t2 = ...;

t1 -> s1.get() // gets int2 -> s1.put(32) // blocks

t1 -> s1.get() // gets int2 -> s2.put(4) // gets in

P d C C di ti


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public class Share {private int s;private boolean empty = true;

public synchronized int get() {while (empty == true) {

try {wait(); // nothing to get, wait} catch (InterruptedException e) {}

}empty = true;

notifyAll(); // wakeup waiting Consumers/Producersreturn s;}public synchronized void put(int s) {while (empty == false) {

try {wait(); // no room} catch (InterruptedException e) {}

}this.s = s;empty = false;notifyAll(); // wakeup waiting Consumers/Producers

}}

Producer Consumer Coordination

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