El Kuba Home::Computers

Java Notes

no guarantee

Last change May 21, 2005 AD

Index

• Notes
  • notes for which I haven't found any other place :-)
  • packages & directories: friend and enemy
• APIs (Application Programming interfaces) and other
  • Networking (RMI, Sockets)
  • Threads -
  • JavaBeans -
  • GUI and Graphics in Java (Swing, AWT, Java2D , Layouts ...)
  • Strings
  • RegExps: Pattern & Matcher
  • File I/O
  • Observer/Observable
• Other (utilities, non Sun APIs ...)
  • makefile for Java
• Tools etc.
  • jdb - debugger
  • JAR archives
  • JavaDoc comments
  • Security and policytool
  • GCJ - Java to native code GNU Java Compiler (+libraries, Java interpreter etc.)
  • NetBeans IDE
• Links you can need

Notes

• Destructor: Java hasn't anything like that. You can write your clean-up code in the method void finalize() and somewhere in the beginning of your code write System.runFinalizersOnExit(true); to ensure it will be called. But runFinalizersOnExit is deprecated for it's unsafe (in multithreaded program?). See Java API documentation.
• javadoc: if you have an interface class (1 file) and its implementation class (2nd file), you can compile them either together or first the interface and then the implementation.

Packages

To make your source file to be part of a package, type in the source "package package_name;".

Packages & Directories

This is our file/directory structure:
java> ls
 mypackage
java> ls mypackage
 MyInterf.java
 MyImpl.java

Compile .java source by javac:
java/mypackage> javac MyInterf.java MyImpl.java

Compile .class source by rmic (assume we want to use RMI) - notice we are in java/ and we don't mention the extension:
java> rmic mypackage.MyImpl

And, finally, let's run it by java (if we indeed use RMI, we have to run rmiregistry first) - notice we are in java/ and we don't mention the extension:
java> java mypackage.MyImpl

Packages revisited

                       home
                           |- worm
                                     |- net
                                     |      |- Network.java
                                     |
                                     |- chat
                                             |- ChatMessage.java

Ex (the compiler's output not shown):
home> ls
  worm
home> javac worm/chat/ChatMessage.java
home> javac worm/net/Network.java

Security

- run "policytool" to create/change a policy file (see this article- also about cryptography and security in general, in Java)
- the policy file for your application is in the java.security.policy system property
- if you run a program and set policy to a non-existing file, java won't tell you it can't find the file, so you may believe everything is OK, until something doesn't work because it hasn't the permission it
needs (I guess that if java doesn't find the policy file, it uses the default one)

Granting permission (copied from the article mentioned above):
***
                   When granting permissions, you can base them on who signed the code, where the code came from (the codebase), or grant them to everyone.
                   The java.security.Permission class serves as the base class of all 1.2 permission-related classes. What an actual grant statement
                   looks like in the policy file follows. This would allow write access to the local temporary directory, and all subdirectories recursively, for code
                   signed by JavaJoe and downloaded from http://www.TrustedUserHome.foo. If an asterisks (*) was used instead of a dash (-), the
                   permissions would be for only the specific directory, not its subdirectories, also.

            grant signedBy "JavaJoe", codeBase
                       "http://www.TrustedUserHome.foo" {
                    permission java.io.FilePermission "c:\\temp\-";
                   }
***

For checking the current permissions, you can use AccessController.checkPermission (Permission perm) - if the permission is not granted, it throws the
AccessControlException that is a subclass the SecurityException. "perm" is obtained by a constructor (which takes, e.g., an object and the operation that shall be performed as
parameters). (System does the checking for permissions by itself, except for your own defined perm.).
 

Networking

Networking Notes

•      get IP address of your computer: java.net.InetAddress.getLocalHost(); returns InetAddress (when printed, it's HostName/HostAddress). You can use InetAddress's methods .getHostName() and .getHostAddress() to get the name/IP (both return String). See javadoc for InetAddress.

RMI 1 - notes

Note: 'remote object' is also called 'remote service' (for it indeed provides a service to the callers) (and 'service' is wide used, e.g. for rmiregistry)
Terminology:
 

• host - the machine running the remote object (and rmiregistry)
• client - the program asking to use a remote object (service)

Notes:

• Naming&lookup: usually they say the address should be "http://...", but in 1 article there was "rmi://..."
• http or ftp server must be running, as a class file provider (unless the client has the necessary .class files (stub) on its classpath) (see also RMIClassLoader)
• rmiregistry must be started from the directory including the .class files (otherwise it won't find your stubs), unless you set correctly the codebase property (assume your stubs are in the 69/ directory on the local disc and aren't in any package):

$> java -Djava.rmi.server.codebase=file:/home/YAK/69/ MyRMIServiceProgram
• both client and server must have the interface def. (and stub, if you don't won't to bother with downloading them) files before they start to communicate
• if you run the server&client locally, from the same directory, you don't need to use security manager and policy file.
• codebase and downloading stubs (observations by one developer)

Registry

• See Registry interface (Sun),  java.rmi.registry.LocateRegistry (Sun; among others has methods to run rmiregistry [createRegistry], obtain a reference to a remote registry [getRegidtry]).
• Starting rmiregistry from within the program, if not yet started:

import java.rmi.registry.*; import java.rmi.RemoteException;
try {
     LocateRegistry.createRegistry( Registry.REGISTRY_PORT );
 } catch ( java.rmi.server.ExportException exex ){
     if( exex.detail instanceof java.net.BindException){
          // do nothing, registry already running
     } else {
          // this is an error, should be solved somehow
     }//if-else is BindException
 } catch ( RemoteException remi ){
     // this is an error, should be solved somehow
 }//try-catch get registry
• set the codebase (it can throw SecurityException; the protocol and the trailing slash are very important):

// protocol + current directory (of the VM) + trailing slash
String codebase = "file:"+System.getProperty("user.dir")+"/";
System.setProperty( "java.rmi.server.codebase", codebase );

Remote Class Loading

• via http/ftp server (=> must be running)
• certain properties must be set when the JVM (=>application) is run (form is: $> java [ -D<PropertyName>=<PropertyValue> ]+<ClassFile>)
• java.rmi.server.codebase is an URL and specifies where are the supplies classes for objects sent out of that machine (either http:, ftp: or file:)
• ? both rmi client and rmi server need a SecurityManager (or at least one of them)

Errors (Exceptions):

   1.Connection refused
     a) when running the client:
     java.rmi.ConnectException: Connection refused to host: 130.236.230.140; nested exception is:
      java.net.ConnectException: Connection refused
     This may mean that the server class or rmiregistry is not running (by 'server class' I mean the class which creates&binds the remote interface implementation, in its main() method.
     b) when running the server:
     - the same output as above, only instead of the IP number you will see 'localhost'
     In this case it's likely that rmiregistry is not running.

RMI 2 - complete example

Part 1 - server

1. define a remote interface (which specifies what methods are available remotely)
2. subclass an appropriate RMI server class ("server" implements the rem.interface)
3. run the rmic compiler on the server class (=>generates stub and skeleton files)
4. register the remote object with the RMI registry (contains bindings name-reference)

ad 1) def. rem. interface

1. def. new interface
2. make the interface extend the interface java.rmi.Remote
3. def. any methods which are going to be available remotely (must by public)
4. each method must declare that it throws the java.rmi.RemoteException

Note: the interface may contain only 'remote' methods.

ad 2) subclass server

• specify the remote interface(s) being implemented by the server
• optionally subclass a remote server (e.g. java.rmi.server.UnicastRemoteObject) (Note: if the server doesn't subclass some of the server classes, than we need to "export" it - so it will wait for remote calls on an anonymous port, usually 1099 - explicitly [in the constructor, I think])
• implement the methods def. in the rem. interface
• def. a constructor for the server, must throw java.rmi.RemoteException
• create and install the java.rmi.RMISecurityManager
• Note: the implementation must implement the remote interface directly (not via its parent class). Otherwise rmic won't compile it.

import java.rmi.*;
import java.rmi.server.UnicastRemoteObject;

public class RMIServer extends UnicastRemoteObject implements MyInterface{
    public RMIServer() throws RemoteException {
        super();
        try {
                System.setSecurityManager(new RMISecurityManager());
                Naming.rebind("//www.liu.se/~yak/RMIServer",this);/* bind name and reference in registry, so a client can search there for "RMIServer" and obtain a reference to it */
        } catch (Exception e) {
                System.out.println("RMIServer error"+e.getMessage());
                e.printStackTrace();
        }
    }//constructor

/*implementation of the interface method*/
    public String sayHi(String name) throws java.rmi.RemoteException {
    return "Hi "+name;
  }

    public static void main(String args[]){
        try {
            new RMIServer();
        } catch (RemoteException e) {
                System.out.println("RMIServer error"+e.getMessage());
                e.printStackTrace();
        }
    }
}// server class

ad 3) runing the rmic compiler

ad 4) starting the registry

Part 2 - client

public class RMIClient {
    public RMIClient() {
        try {
            // get reference to remote obj.from the rmiregistry:
            MyInterface remobj = (MyInterface) Naming.lookup("//www.liu.se/~yak/RMIServer");
            // invoke a remote method
            System.out.println( remobj.sayHi("Dick") );
        } catch(Exception e) {
                System.out.println("RMIClient error"+e.getMessage());
                e.printStackTrace();
        }

    }// constructor

    public static void main(String args[]){
        new RMIClient();
    }
} // client class

Sockets

Sockets & ObjectInput/OutputStream

• the ObjectInputStream's method readObject is blocking (i.e. blocks until there is something to be read). I haven't discovered any reliable way to determine whether there is something or not, in the stream.
• changing an object: if you send an object, change it (e.g. change some of its fields) and send it again, the receiver receives exactly the same object as before, namely the change doesn't take effect (from the receiver's point of view). Conclusion: you can't change the object after it has been sent, you must create a new one (e.g. create a new object which is a copy of the old one, change it in the desired way & send it).

Threads

(source: Java for Practitioners, John Hunt)
- independently running processes
Possible states: runable([R]), sleeping([S]), waiting([W]), interrupted([I])
start()->[R]-sleep()->[S]-time out()->[R]
             [R]-wait()->[W]-notify()->[R]
[?]-interrupt()->[I]
[?]-stop()->dead

Creating a thread

• sublcass Thread and redefine run()

Ex:
public class Scroller extends Thread {
    public void run() {
        while(true) { ... perform whatever you want ...}
    }
}
...
Thread t = new Scroller("scroller thread");
t.start(); //started
 
• anonymous Thread subclass

Ex:
Thread th = new Thread("printing anonymous thred") {
                        public void run() {
                            System.out.println("Running!");
                        }
                    };
th.start();
 
• define a class implementing Runnable interface. It must define run()

Ex:
public class Scroller implements Runnable {
    public void run() {
        while(true) { ... perform whatever you want ...}
    }
}
...
Thread t = new Thread(new Scroller());  //note the difference against the previous case
t.start(); //started

Some methods:

Synchronization

1. synchr. methods inside the same class (it means that only 1 of the can run at a time; if another wants to run. must wait till the running one finishes). Use 'synchronized' keyword in the method definition: public synchronized void method(){...} There is one more way (to synchr. only a part of a method)
2. synchr. 2 threads (thread tTwo waits until tOne finishs): (in the body of tTwo) ... tOne.join() ... code executed after tOne terminates

Thread interaction

JavaBeans

JavaBean is distinguished from a normal class by:

• Providing a public no-argument constructor
• Implementing java.io.Serializable
• Following JavaBeans design patterns (at least one public property must be defined)
  • Set/get methods for properties
  • Add/remove methods for events
• Java event model (as introduced by JDK 1.1)
• Being thread safe/security conscious
  • Can run in an applet, application, servlet, ...
• And, optionally, having associated BeanInfo class (which is sometimes necessary, e.g. for some GUI builders)

Properties:

Events:

Bean Notes

BeanInfo

BeanBox tool

JAR archives

Creating jar file:

Extracting jar file:

Creating and executing executable jar file:

New way (java >= 1.2)
Though I have java 2SDK, version > 1.3, I haven't managed to used the new way (though I followed the instruction). It should work as follows:
$> find worm/ -name '*.class' | xargs jar cmf main.txt worm.jar
- create jar archive, merge the manifest with the specified file; in this case, main.txt contains a single line: "Main-Class: worm.Worm"
$> java -jar worm.jar
-run the package. For me it always throws "Failed to load Main-Class manifest attribute from worm.jar". I wonder why.

GUI and Graphics in Java

AWT

• if you want your component to have a particular size, you need to redefine getPreferedSize: Ex: public Dimension getPreferredSize() {return new Dimension(400,300);}
• values returned by getWidth() and getHeight() are derived from the values set by setSize(). So if you just redef. getPreferredSize, the component will have the size you want, but these two functions will return zero.

Enable closing your window (probably a subclass of Frame):

1. let your window implement the WindowListener
2. in its constructor, call addWindowListener(this)
3. define the listener's methods (must be public) - leave them empty (methodName(..){}) , except:

public void windowClosing(WindowEvent we){ System.exit(0); }
OR

• in the window's constructor, call addWindowListener(new MyHandlerName)
• define inside the window the MyHandlerName class, which extends WindowAdapter
• in MyHandlerName define public void windowClosing(...) as above

LayoutManager
GridBagLayout (gbl) is one of the most advanced; requires a GridBagConstraints (gbc) object to be used
1. set constraints (gdc.weightx=?,.weighty,.fill,.gridx[column],.gridwidth[how many columns occupies] etc.)
2. apply the constraints(before adding a component): gbl.setConstraints(Component toBeAdded, gbc)
3.add component to the container (add(toBeAdded);)

Swing

• content can't be added directly to a JFrame; its pane (Container pane = this.getContentPane();) is used instead of it. (pane.add(aComponent)).
• use paintComponent() instead of paint()
• if you want to use Swing in an applet, it must be JApplet (the current browsers have troubles with that, use rather AWT and Applet). Most of the current browsers do not manage Swing, it's better to use AWT. Otherwise it becomes quite complicated.

Layouts etc.

BorderLayout

• north, south - only its width will ever grow
• west, east - only its height will ever grow
• center - grows in both directions

GridBagLayout

• Constraints:
  • gridx, gridy - the 'coordinates' of the left-top cell occupied by a component
  • gridwidth, gridheight - how many cells in a row/column does the component occupy (they're 'merged' into one large 'supercell')
  • fill - in what direction does the component's cell (or 'supercell')  expand (BOTH, NONE - keeps equal size ...)
  • anchor - where in the cell is the component placed (this is not important if fill==BOTH, for in the case it fills the whole cell)
  • weightx, weighty - if the container grows, these values determine what part (ratio) of the growth the (super)cell 'receives' (E.g. if you have 2 components in a row, with the weightx 0.3 and 0.6, the 2nd will grow twice more).
• the weights (weightx, weighty) of all columns/rows shall be equal. If the total weight of a column/row (e.g. 0.6) is smaller than those of the others (e.g. 1.0), the layout manager gives the difference weight to the last component of the column/row, i.e. expands it so to fill the remaining space (in this case it would receive the additional weight 1.0 - 0.6 = 0.4)

Java2D

Animation

1. in the first call initialize a non-local variable of the type AffineTransform , called e.g. aAT, to contain the identity transform (aAT = new AffineTransform; does it). Use this way, not aGraphics2D.getTransform()!
2. all the transforms (rotations, translations) you want to apply to your object, apply to aAT (e.g. aAT.translate(30,0) or aAT.rotate(Math.PI, rotationCentre.x, rotationCentre.y) )
3. before you draw the object, apply the transformation done so far to the graphics object, via its .transform(...) method. Don't use setTransform(...)! The trouble with .getTransform() and .setTransform(...) is that they sometimes give strange results, especially if you use them to get, remeber and restore a transform between calls. They should be used only inside one call, to get and reset the unchanged transform (e.g. at the very beginning you use getTransform, then you apply a transform for one of your objects via .transform(...), then you reset the initial transform via setTransform and apply a transform - via .transform(...) - for another object).

Ex: aGraphics2D.transform(aAT);

• And, finally, you can draw your object: aGraphics2D.draw(myObject);
• Because you applied all the transforms to a non-local variable aAT, they will be preserved between calls of the paintComponent(...) and if you want to get where you finished the lust time, just use aGraphics2D.transform(aAT);

Backwards mapping

Strings

• '==' can't be used to compare two strings, you must use the .equals method
• StringTokenizer class can be used to split a string into parts (much simpler than the StreamTokenizer)

RegExps: Pattern & Matcher

String text = "11 22    3.33 a string to be matched"
// 1. Create a pattern
// Here: something line " int int float any_text...". \\s = whitespace, \\d = decimal.
java.util.regex.Pattern pattern = java.util.regex.Pattern.compile("(\\s*\\d+){2}(\\s*\\d+\\.\\d+).*");
// 2. Get a matcher for it
java.util.regex.Matcher matcher = pattern.matcher( text );
// 3. Find a match. The matcher remebers its position (last match) in the string.

// Find the next match and print it. group can only be called after a successful find.

if( matcher.find() ){ System.out.println( matcher.group() ); }
// 4. Reset the matcher to start searching the string from the beginning.
matcher.reset()     // Reset its inernal state => find() would find the first match

File I/O

Write/read a string into/from a file:

import java.io.*;

PrintWriter writer;
File file = new File("myfilename");
try { file.createNewFile(); } catch (IOException e) {/*do something*/}
try { writer = new PrintWriter( (new FileOutputStream(file)), true);/*autoflush on*/ } catch (FileNotFoundException e) {/*do something*/}
writer.print("something"); /*or println */
/* ... */ writer.close();
---
try { 
    BufferedReader reader = new BufferedReader ( new FileReader("myfilename") );
    String s = reader.readline();
} catch (IOException e) {/*do something*/}
reader.close();

JavaDoc Comments

- run javadoc (include a list of all packages adn subpackages in the project):
$> javadoc -d mydir/ -private -windowtitle 'WormDoc' worm worm.bug worm.net worm.chat

- used when generating HTML documentation via javadoc
- of the form /** comment */
- keywords: @author, @version,, @see (what shall the reader read else, form package.Class#method(type,...)),
        (function:) @param(required, form @param name type description), @return(required unless void or constructor), @exception

- HTML tags may be embedded
- break each line that has over 80 characters

- javadoc omitts some tags by default (author, version). May be changed by options when running the javadoc( e.g.- author, -version)
- use -d flag to specify the destination folder: $> javadoc -d mydirectory/HTML MyClass.java

Style etc.
- the first sentence (closed be period followed by space/tab/line break) shall be on overview of the class/method
- use <code></code> tag for keywords, package names etc.
 

Ex:
/**
  *  This counts the number of drivers killed per month.
  *
  *  @author Jakub Holy
  *  @see CountAccidents
  *  @param highway_part part of the highway we are interested in
  *  @exception TooManyDeadException rised when the number of dead exceeds MAX_DEAD
  */
...

jdb debugger

• suggestions: when you create a thread in your code, give it a name. The debugging will be much easier[ new Thread(String name)].
• compile with the -g flag: > javac -g MyClass.java
• start debugger: > jdb MyClass (TCP/IP networking service must be running)
• some commands: help (or ?), exit (or quit), print myvariable, ...
• thread id: don't be confused by the documentation. Thread's id is the value including 'x' (0x97 in the following example). At least sometimes.

Ex: (java.lang.Thread)0x97                         main              running

Other

• gcj is a Java to native code (e.g. assembly code) compiler by GNU (open source)
• SWT - Standard Window Toolkit - is st. between AWT and Swing (it uses native components if there are any, otherwise draws them itself => looks more natural than Swing and has more widgets than AWT). By Eclipse (open source).

synchronized key word

Used to synchronize threads on an object (so that only one thread can access the object at time, the others have to wait).
Use:

1. synchronized method method() of an object obj: if a thread calls obj.method(), the other threads who call obj.method() (on the same object) have to wait until its call returns. (Note: also static methods may be synchronized)
2. synchronized block of statements has the form: synchronized(object){ statements }. Only one thread may be executing the block (the statements) for the object at time.

Makefile for Java

GCJ - GNU Java Compiler

My version of gcj: cygwin gcj 3.2; Today: June 1 2003

Limitations of GCJ

• So far gcj compiled Java into native code cannot use Threads for they are not available. When the program is run it throws exception "Java.lang.InternalError: Thread.start called but threads not available". Source
• It seems to me that gcj can compile into native code only .class files created by gcj.

Notes

Compile (Java to native code):

1> gcj -c mypackage/MyJavaProg.java
2> gcj --main=mypackage.MyJavaProg -o myprog.exe mypackage/MyJavaProg.o

Or both in one step:
> gcj --main=mypackage.MyJavaProg -o myprog.exe mypackage/MyJavaProg.java

- Flags: '-c' = compile to object (.o), '-o name' =  give name to the output, --main tells gcj name of the class that contain the main() method that shall be run
- Other flags for the 1st line: '-C' = compile to .class, '-ggdb' create debug info. for gdb, -On where n=nothing or 0..3; perform optimization of the given level, 0 implies no optimization.
- It seems to be better to compile like this, not .java->.class->.exe (less troubles).

If you compile with cygwin gcj 3.2 it prints pretty often a warning like this: "/cygdrive/c/TEMP/cczKbTsy.s:93: Warning: .stabs: description field 'a0006' too big, try a different debug format". It's a bug in the compiler itself which prevents it from creating debug info thus making it produce useless information about exceptions. GCJ produces by default some debugging info in the stabs format (hence '.stabs'). It's highly recommended to use another - not buggy - debug format (-gdwarf-1, -gvms, -gxcoff etc.).

Debug with GDB

You must set GDB to ignore the signals used by Java garbage collector:

(gdb) handle SIGPWR nostop noprint
(gdb) handle SIGXCPU nostop noprint

GCJ Links

Compiling Java with GCJ, Debugging Java with GDB

NetBeans Integrated Development Environment

version 4.0

Compile with "-deprecation": Tools->Options->Building->Ant Settings, click to the right of "Properties" (...), type on a new line "javac.deprecation=on".

Create a new GUI JavaBean that can be added to the Palette: see NetBeans: the Definitive Guide. It refers to an older version but still it's usable.

version 3.5.1

Create new project using CVS (a versioning system)

Out of NetBeans:

1. Create a directory (you want to hold the project in)
2. Add it to a CVS repository (how to); don't forget to check it out and work with that version (to ensure that Cvs subdirectory is there).

Inside NetBeans:

3. Create a new project (Project->Project Manager, click "New")
4. Mount your directory as a CVS repository (File->Mount Filesystem, select Version Control->CVS; enter required info [connection method is perhaps "Local"])

Links

SUN:

• Java APIs etc.
  • RMI
    • Remote Obj. Activation (sun)
    • RMI Activation (part1, part2) - services, RMID etc. in JavaScpaces
    • Getting Started RMI (ida)
    • RMI homepage at Sun
    • RMI tutorial & motivation, really nice
  • JavaSpaces: install&set, compile, run
  • Java Web Start - article
• developer.sun
  • tutorials - very useful (language, swing and many others)
  • RMI 'short' course by jGuru (also explains the rmi architecture ...) - includes also a working example (the only one out of 3, that I was able to run :) and the description how to install RMI software over more machines
• Java 1.4 Specification (javadoc documentation)

Others:

• Java Glossary - quite useful, includes also stuff (SW...) related to Java.
• Java Gaming
  • Java Graphics and Gaming - a textbook, 2004 AD.
  • JavaGaming org.
  • Older: Article about Java games (local copy), Future of Java Gaming in the new millenium
• IBM - tutorials etc. (also about Linux, XML ...)
  • Developer Works (tutorials ...)
  • JavaBeans Intro and JavaBeans Guidelines by IBM
  • Java Antipatterns
  • Tetris programmed using JavaBeans
  • Robocode - great!!!! Learn Java by programming fighting robots!
  • fast GUI (native) using SWT(Standard Window Toolkit) and gjc (GNU Java compiler)
• Java related Open source and Freeware
  • Ant - does the same as 'make' at UNIX, but is Java and XML based (and very useful, say many people)
  • Eclipse - various (SWT ...). Org. founded by Borland, RedHat, IBM ...
• Tutorials etc. out of sun/IBM
  • Bladwin's serie of (advanced Java) tutorials
  • code samples by Cliff Berg (indeed good!) [printing, remote object browser and many more]
  • layouts - links to various layouts (not only the standard ones)
• Sites, journals etc.
  • developer.com (former gamelan.com) - lot of articles related to web and especially Java
• Libraries etc.
  • The Skin Look and Feel is a special LF which supports themes and can use any GTK and/or KDE theme, or theme packs made from them. It's an easy way to make your application skinnable. An example of use. Some additional Swing components.
• Various
  • Jars.com - the number one Java™ review service. (Top 1%).
  • IBM SDK for Linux (1.4.1 .tgz has 54.2MB, JRE .tgz 35.1MB).
  • IzPack - an installers generator for the Java platform producing lightweight installers; GPL.

by Jakub Holy 2002 AD