java overview. aqute copyright © 1999 all rights reserved presentation 10/01/2000 ericsson about me...

aQute Copyright © 1999 All rights reserved presentation 10/01/2000 ERICSSON

Java Overview


About me

Peter Kriens Work as a consultant

(mainly for for ERICSSON) Finnasandsvagen 22 43933 Onsala, Sweden +46 705950899 [email protected]


History

1990 SUN starts crash team under Patrick Naughton Carte blanche to clean up the software mess at SUN Gosling created OAK for embedded devices (!) Products all failed

1993 Mosaic, the first web browser was born Somebody realized the combination: Applets Language became the product


History

1996 JDK 1.0 released Focused on Applets, lousy graphics 8 packages, 4Mb download

1997 JDK 1.1 released Better graphics, reflection, security (try), beans, RMI,

ZIP files 22 Packages, 9 Mb download


History

1999 JDK 1.2 SE released Lightweight UI (!), collections, security (again), JAR

files, Native interface change… 59 packages, 20 Mb download

2000 JDK 1.3 SE in beta Improvements ... 77 packages (so far), 25 Mb download


Quick Tour: Hello World Getting started

Content of file: HelloWorld.java /**

* Small hello world example class. * */public class HelloWorld {

public static void main( String args[] ) { System.out.println( "Hello world"

+ (args.length >= 1 ? args[0] : "whoever") );}

} javac HelloWorld.java java HelloWorld peter

Hello world peter

That is all ...


Quick Tour: Objects

Creating a class Content of file: Point.java /**

* A Simple point class. */public class Point { double _x; // Instance variable double _y; public Point() { this(0,0); } public Point( double x, double y ) { _x=x; _y=y; } public double getX() { return _x; } public double getY() { return _y; } public double getLength() { return Math.sqrt( getX()*getX() + getY() * getY() ); } public Point translate( Point t ) { return new Point(getX() + t.getX(), getY() + t.getY() );}}


Quick Tour: Not to be an Object

Not all variables are objects like in Smalltalk int, char, boolean, long, double, float, byte are

<primitive> types. Each primitive type is represented by a class in

java.lang public class HelloWorld {

public static void main( String args[] ) { int length = args.length; Point p = new Point( length, length ); }}


Quick Tour: Inner class

Everything had to be a class. Callbacks require their own class

Too cumbersome to specify in other file, so special syntax was wrought (ugly!):

public static void main( String args[] ) { Point p = new Point() { public double getX() { return super.getX() * 2; } };


Quick Tour: Garbage Collection

Java cleans up after you /* GC */

...Point p = new Point();p = p.translate( new Point(10,10) );...

Previous code creates 3 new objects No need for destructor. No need for delete


Quick Tour: Inheritance

Classes can be extended /* Extending point class */

public class Point3 extends Point { double _z; public Point3() { _z=0; super(0,0); } public double getZ() { return _z; } public double getLength() { return Math.sqrt( getX()*getX() + getY()*getY() + getZ() * getZ() ); } ...}

Only use it for an "is-a" relationship Powerful but easy to overdo


Quick Tour: Inheritance Single inheritance only All classes inherit from class Object A Class is a an instance of class Class

So the class Class is an instance of Class (!) Class objects can be used as normal objects

Reflection ClassLoaders

"super" keyword to access super class


Quick Tour: Interfaces

Used for specifications /* Interfaces */

public interface Compare { public int compare( Compare t );}

class CPoint extends Point implements Compare { public int compare( Compare t ) { Point tt = (Point) t; return getLength() - t.getLength(); }}

Decouples using from implementation Very popular with specifications


Quick Tour: Interfaces

Logclient

SimpleLog

IBMLog

MotorolaLog

implements

usesinterface

public interface Log { public void log(String s);}

public class SimpleLog { public void log(String s) { System.out.println( s ); }}


Quick Tour: Exceptions

Exceptions are used to separate normal flow of program from error cases

Runtime exceptions: public class HelloWorld {

public static void main( String args[] ) { System.out.println( "Hello world"

+ args[0] );}

}


Quick Tour: Exceptions

Checked exceptions: public class HelloWorld {

public static void main(String args[]) throws IOException { FileOutputStream out = new FileOutputStream( "temp" ); out.write( args[0].getBytes() ); out.close();

}}

Exceptions can be very messy


Quick Tour: Exceptions Handling exceptions:

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

FileOutputStream out; try { out = new FileOutputStream( "temp" ); out.write( args[0].getBytes() ); out.close(); } catch( IOException e ) { System.out.println( "Exception " + e ); e.printStackTrace(); } finally { try { out.close(); } catch(Exception ee) {} }

}}

Never ignore exceptions: catch(...) {} Easy to overdo exceptions


Quick Tour: Packages Name spaces for Java

package = add a class to a package import = use classes from a package

Encapsulate a number of related classes Used for access control

Content of file: ../se/aQute/plane/Point.java package se.aQute. plane;

import se.aQute.basictest.*;public class Point { double _x; double _y; public Point() { clear(); } ...}


Quick Tour: Equality Equal and identical are different concepts Identity check is == Class Object has method equals(Object o)

method that is identity 3 == 3; // YES "three" == new String("three"); // NO "three".equals( new String("three") ); // YES

Classes can override equals(Object o) for their semantics Watch hashCode() when overriding equals() !!!


Quick Tour: toString()

toString() is a useful method for debugging Each object inherits a default implementation

from Object Overriding can be very, very useful during

debugging public class Point {

. . . public String toString() { return getX() + "," + getY(); } . . .}


The Java VM

Java is compiled to byte codes Byte codes are interpreted by the VM

javaccompiler

public class HelloWorld { public static void main( String args[] ) { System.out.println( "Hello world" ); }}

File: HelloWorld.java

File: HelloWorld.class

javaVM

0xCA 0xFE 0xBA 0xBE 0x01 0xF7 0x76 0x41 0x23. . .

Hello world

rt.jaror

classes.zip


Native code interface

Native code interface through JNI Native interface defined in Java class

class Native { int var; public native int foo();}

Translated via javah into C header file #include <native.h>

typedef struct ClassNative { long var; } ClassNative;HandleTo(Native);extern long Native_foo(struct HNative *);


The Java VM: The good news

Portable format allows execution on many different computer types

Hundreds of VMs available from different vendors

Optimized for certain applications Inherently safe


The Java VM: The bad news

Interpretation requires CPU cycles Instruction set not optimized for target machines Byte format is rather verbose


Is Java Cool? Nothing particularly innovative

Portable object code from Pascal (P-code!) Syntax from C++ Object model from Smalltalk Garbage Collection from Lisp

Reasons for success: People were getting fed up with C++ Java looked much simpler Applets kick started it (but no longer drive it)


The runtime library

The runtime library is Java's best asset Single implementation of common code Some implementations are pretty bad (AWT!)

Library has grown very hard From 8 packages to 77 packages! Need for profiles

There is an amazing amount of code to be found on the net


The runtime library: java.lang

Basic package which is always included Contains primitive type classes for Boolean,

Integer, Double, Float, Byte, Character, Void number <-> string conversions number <-> number conversions Max/Min values Used in reflection


The runtime library: java.lang Process, Runtime and System for access to

system resources Running of external processes and linking of external

libraries Debugging Memory interface Time System properties Utiltity functions like arraycopy



Thread, ThreadGroup for threads A Thread is like an internal process Run multiple threads at the same time Combine threads in a group for security control Monitors are used to manage shared resources

Math = Math library Contains mathematical routines sqrt, cos, sin, log, ln ...



Throwable Base class for Exceptions and Error

SecurityManager for security Performs security checks (when installed) Access to call stack


The runtime library: java.lang String Unicode!

16 bit char = 65536 possible characters Functions

String can be concatenated with + System.out.println( "File : " + file + " : " + exception );

substring, indexOf, trimming Conversion from number to String Symbols (unique value with intern() )



StringBuffer Used to concatenate strings

Expensive: String concat = "";

for ( int i=0; i<10; i++ ) concat = concat + i;

Less Expensive StringBuffer sb = new StringBuffer();

for ( int i=0; i<10; i++ ) sb.append( "" + i );String concat = sb.toString();


The runtime library: java.io

Streams are used for byte access to files Readers/Writers are used for Unicode access Streams, Readers, Writers can be used as pipes

Buffering Data access (e.g. getInt(), getShort() ) Between threads (PipeXXXXX) Conversion from stream to reader/writer

ObjectStreams


The runtime library: java.net

Access to the net (TCP/IP) InetAddress

Stream connections: Socket, ServerSocket Extendable: SocketImplFactory

URL, URLConnection Extendable: URLStreamHandlerFactory

Datagrams Unicast/Multicast


The runtime library: java.util Useful classes

Collections: Vector, Hashtable, BitSet, Properties, Stack, Enumeration, Map, Array, Iterator

Time: Date, Calendars, TimeZones Locale: Locale, ResourceBundles Random Observable StringTokenizer EventObject, EventListener


The runtime library: other

java.rmi Remote method invocation support

java.math Big Integer (unlimited digits) for private/public key

calculations


The runtime library: more other java.security

Classes for certificates, principals, permissions java.sql

Access support to SQL databases java.text

Support for language independent messages java.util.zip

Access to zip files which are the preferred delivery vehicle for java applications.


The runtime library: more other

java.util.jar Access to jar files and their manifest

java.lang.reflect Access to objects in runtime via reflection on their

interfaces java.beans

Support for Java beans


The runtime libraries: GUI

Original AWT in 1.0 was … well, awful JDK 1.1 at start 1997 improved significantly Netscape released lightweight GUI called IFC at

that time SUN decided to develop their own lightweight

GUI at the end of 1997 Netscape joined them SUN team and stopped

support for IFC


GUI: AWT Uses peer model

A widget controls a native widget Supports "native look and feel"

Event model: first based on single dispatching method handleEvent Today based on listeners

Layout managers LightWeight components


GUI: AWT looks


GUI: IFC Derived from NeXT, adopted by Netscape Lightweight components Very clean code, small, reliable and included in

Netscape Communicator Internal windows, drag & drop Event handling via strings Powerful GUI builder called Constructor Available (including source) but not maintained


GUI: IFC example, full control


GUI: JFC Derived from IFC (same people [@ start]) Lightweight components, listeners

JButton top = new JButton("Top");top.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { System.out.println("top"); }} );

Compare Smalltalk, there it would be:Button top = Button new: 'top'.top action: [ Transcript print: 'top' ].

HUGE Based on Model-View paradigm & Pluggable UI Easier to use than it looks


GUI: JFC complexity, the button

AbstractButton

JButton

ButtonModel

ButtonUI

DefaultButtonModel

L&F...

JToggleButton

JRadioButton

JMenuItem

JCheckBox

MenuItem JMenuJRadioButton

MenuItemJCheck

Box


JFC: The good and changing looks


Components: Beans Components are wrapped objects Access via reflection Allows runtime composition of systems (via end users?): Visual Programming Properties can

be set via strings

BeanProperties

Methods Events


Java Beans Events follow the listener model

SomeBean bean = new SomeBean();bean.addTickEventListener(new TickEventListener() { public void tick(TickEvent e) { System.out.println("tick");}});

Properties are defined via methods that start with get/set

E.g. property "tickCount"public class SomeBean { public long getTickCount() { … } public void setTickCount() { … }}

Bean programmer can override defaults with an Introspector


The Bean Box


Enterprise Java Beans

SUN's attempt to enter the enterprise computing market

Mainframe connectivity Application Servers Message Queues Transactions

EJB client


Servlets Very popular way to create WWW pages Offers: User sessions, Parameters, Cookies Not always easy to setup in web server Life cycle managed by web server A simple servlet:

import javax.servlet.http.*;import javax.servlet.*;public class HelloServlet extends HttpServlet { public void doGet( HttpServletRequest rq, HttpServletResponse rsp ){ rsp.setContentType( "text/plain" ); PrintWriter out = rsp.getWriter(); out.println( "Hello world " + rq.getParameter("name") ); }}

http://host/servlets/HelloServlet?name=peter


Servlets

Web Server

Java VM

ServletA

Servlet B

Clienthttp://a.com/servlets/A?name=peter

HttpRequest HttpResponse

Mime typed data, e.g. HTML


Java Server Pages

HTML pages contain embedded Java code Uses bean standard Beans can be page local, session local or global Pages are pre-processed for speed Easy to design good looking pages with standard

tools


Distributed Programming

Remote Method Invocation RMI Common Object Request Broker Architecture

CORBA Voyager (ObjectSpace)

Process A Process B

String s = foo("bar")


RMI

Strongly based on Remote Procedure Call Uses serialization of objects for parameters Name server

Compute

Remote

Engine

UnicastRemoteObject

Client Stub

Skeleton

rmic

Connection made vianame server


RMI

Not all objects are serializable Code transfer awkward

Current RMI does only do class transfer via HTTP (biggest problem in JINI)

Stub skeleton model cumbersome All methods MUST throw RemoteException Built in to all Java VMs


CORBA

Language independent standard for interprocess communication defined by OMG

Uses Interface Description Language (IDL) Every VM has an Object Request Broker built in Java is a very good match for CORBA

But is it needed? No class loading


CORBA

IDL

Stub SkeletonClient

idltojava

Impl.

module HelloApp { interface Hello { string sayHello(); };};

Compute

CorbaObject

Helper

Holder

Confused?


Voyager

Simple implementation using proxy generation on the fly (standardized in Java 1.3)

Runs on all Java VM's: ~270K Does not require pre-processor Does inline class loading Advanced distributed even mechanism


Database interfaces

JDBC Traditional interface to SQL like databases Very much like Microsoft's ODBC

OO Databases PSE from Objectstore POET POS from Oracle


Service Discovery

Discover services available on the local net Broadcast/Multicast, Communication

JINI Pure java, cumbersome, big. Type based

SLP Simple

Universal PNP with SSDP HTTP based, declarative with XML


Media API's

Java 2D Java 3D Java Media Framework JTAPI, Telephony API


Interesting developments JavaSpaces Infobus Java OS Java shared data toolkit Java Embedded Server / OSGi Java mail Java Activation Framework ……………..


Conclusion

Java is a simple but powerful language It has grown too fast too big Library support is extensive Not all APIs are well designed Performance is an issue Significant improvement over C++


References Java: www.javasoft.com Java Developers Connection:

http://developer.java.sun.com IBM source code: alphaworks.ibm.com Voyager: www.objectspace.com PSE Pro: www.odi.com Links to java related:

http://www.taxon.demon.nl/JW


References

Java in a Nutshell David Flanagan. ISBN 1-56592-183-6

Java Secrets Elliote Rusty Harold.ISBN 0-7645-8007-8

Java 2 Performance and idiom guide Craig Larman, Rhett Guthrie. ISBN 0-13-014260-3


References The Java Virtual Machine Specification

Tim Lindholm, Frank Yellin, ISBN 0-201-63452-X Java Security

Scott Oaks. ISBN 1-56592-403-7 Java Developers Almanac

Patrick Chan. ISBN 0-201-37967-8 Late night IFC

Jason Beaver, Jamie Costa, Jason Wehling. ISBN 1-56276-540-X

java overview. aqute copyright © 1999 all rights reserved presentation 10/01/2000 ericsson about me...

Documents

public class point3

public class simplelog

instance of class class

y public point

public double getx

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