Abstract Graphics class ???ques???

Referring to the abstract methods within this class such as drawPolyline and drawPolygon, etc . . . it says in the documentation for Class Graphics:
"The Graphics class is the abstract base class for all graphics contexts that allow an application to draw onto components that are realized on various devices, as well as onto off-screen images."
There are no sub-class method overrides for drawPolyline and drawPolygon, for example, except for those in subclass Class DebugGraphics, which in turn call Graphics.drawPolyline and Graphics.drawPolygon - for example - at the end of the method implimentation anyway.
And besides, DebugGraphics is a swing class, and I would not be importing it in a strictly AWT application anyway.
So where is the actual code for these methods is what I am wondering?
Thanks;
~Bill

The Graphics class is subclassed in JVM specific classes since rendering
graphics on different machines is going to be done differently (this
was discussed recently). So to use these methods find a suitable object
(like an image already loaded) and call getGraphics on it. This will
return a Graphics object cast from the JVM specific graphics subclass...
Steve

Similar Messages

Newbie help needed w/Graphics class!

Hi everyone,
I'm stuck on something I know is very simple to do, but I can't seem to find the right combination. I have a derived class that draws a circle using the graphics class. I'm getting compilation errors when I try to set the color and draw the circle. I have looked thru these forums as well as the API. Below is my code. Any pointers would be highly appreciated!
import java.awt.Graphics;
public class SmartCircle extends SmartShape
SmartCircle(int first, int second, int third, Color c)
super(first, second, third, c);
public void draw(Graphics g)
setColor(Color c);
fillOval(first, second, size, size);
}

Here is SmartShape. It is located in the same directory as SmartCircle, so therefore doesn't need to be imported, correct?
public abstract class SmartShape
//define instance variables
protected int positionX, positionY, size;
protected Color theColor;
public SmartShape()
     //initialize variables
     positionX = 20;
     positionY = 20;
     theColor = Color.white;
public SmartShape(int first, int second, int third, Color c)
     if (first >= 0)
     positionX = first;
     else
     positionX = 0;
     if (second >= 0)
     positionY = second;
     else
     positionY = 0;
     if (third >= 0)
     size = third;
     else
     size = 0;
     theColor = c;
public abstract void draw(Graphics g);
Hope that helps!
Melissa

Return an Image from a subclass to a graphics class

Hello
I'm wondering how to return an Image generated by one class to a class which works as a graphics class. The graphics class is run from a main class. Let me make up a schedule:
Image-generator return Image -> graphics class paint
I have tried just making an Image and using the getGraphics to connect a graphics object to it, but it doesn't seem to work.
Thanks in advance

Okay, here are the pieces of code we use. (Comments are in Swedish but they are barely relevant, and explain merely basically what is happening in the program)
The applet is compilable, but there is a nullpointerexception in Elefanträknaren, at getGraphics(). Believe me, I have tried finding the solution to this already.
Spelet (main method)
import java.applet.*;
import java.awt.*;
public class Spelet extends Applet
     /*Elefanträknaren testerna;*/
     Ritaren ritarN;
     Graphics g;
     public void init()
          /*testerna = new Elefanträknaren();*/
          ritarN = new Ritaren(g, getSize().width, getSize().height);
          setLayout(new GridLayout(1, 1));
          add(ritarN);
     public void start()
          ritarN.startaTråd();
     public void stop()
          ritarN.stoppaTråd();
     public void update(Graphics g)
          paint(g);
}Ritaren (graphics object)
import java.awt.*;
public class Ritaren extends Panel implements Runnable
     Elefanträknaren e;
     Graphics g;
     int bredd, höjd;
     //Trådobjekt
     Thread tråd;
     public Ritaren(Graphics g, int bredd, int höjd)
          this.bredd = bredd;
          this.höjd = höjd;
          e = new Elefanträknaren(bredd, höjd);
     public void startaTråd()
          if( tråd == null )
               tråd = new Thread(this); //Skapa tråden
               tråd.start(); //Kör igång
               e.startaTråd();
     public void stoppaTråd()
          if( tråd != null )
               tråd.interrupt();
               tråd = null;
     public void paint(Graphics g)
          g.drawImage(e.getSpökbilden(), 0, 0, this);
     public void update(Graphics g)
          paint(g);
     public void run()
          while( tråd != null )
               repaint();
               try
                    Thread.sleep(33);
               catch(Exception e){}
}Elefanträknaren (class generating the Image)
import java.awt.*;
import java.util.*;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
public class Elefanträknaren extends Panel implements Runnable
     //Vektorn som innehåller alla Elefant-klasser
     private Vector elefanterna;
     //Ritobjektet för den dubbelbuffrade bilden
     private Graphics gx;
     //Bildobjektet för dubbelbuffringen
     private Image spökbilden;
     private int bredd, höjd;
     //Trådvariabeln
     private Thread tråd;
     //Rörelsen uppdateras 30 ggr/s. RÄKNARE håller koll på när en elefant ska läggas till (efter 30 st 30-delar = 1 ggr/s)
     int RÄKNARE = 30;
     int ÄNDRING = RÄKNARE;
     //DELAY betecknar delayen mellan två bilder/frames. 33 ms delay = 30 FPS
     int DELAY = 33;
     //Konstruktor
     public Elefanträknaren(int bredd, int höjd)
          elefanterna = new Vector();
          this.bredd = bredd;
          this.höjd = höjd;
     //Kör igång tråden/ge elefanterna liv
     public void startaTråd()
          if( tråd == null )
               tråd = new Thread(this); //Skapa tråden
               tråd.start(); //Kör igång
               //Dubbelbuffringen initieras - detta måste ligga i startaTråd()
               //spökbilden = new BufferedImage(bredd, höjd, BufferedImage.TYPE_INT_ARGB);
               spökbilden = createImage(bredd, höjd);
               gx = spökbilden.getGraphics();
     //Stoppa tråden/döda elefanterna
     public void stoppaTråd()
          if( tråd != null )
               tråd.interrupt();
               tråd = null;
     //Lägg till en elefant i vektorn
     private void läggTillElefant(Elefant e)
          elefanterna.add(e); //Lägg till en Elefant som objekt i vektorn
          Elefant temp = (Elefant)     elefanterna.get(elefanterna.size()-1);
          temp.startaTråd(); //Starta Elefantens tråd - ge Elefanten liv
     //Sätter ihop bilden som ska sickas till Ritaren
     public void uppdaterarN()
          //Rensa skärmen från den förra bilden
          gx.fillRect(0, 0, bredd, höjd);
          for( int i = 0; i < elefanterna.size(); i++ )
               Elefant temp = (Elefant) elefanterna.get(i);
               gx.drawImage(temp.getBild(), temp.getX(), temp.getY(), null);
     public Image getSpökbilden()
          return spökbilden;
     //Tråd-loopen
     public void run()
          while( tråd != null )
               RÄKNARE++;
               if( RÄKNARE >= ÄNDRING )
                    läggTillElefant(new Elefant(11, 50, 900));
                    RÄKNARE = 0;
               uppdaterarN();
               //repaint();
               try
                    Thread.sleep(DELAY);
               catch(Exception e){}
}Elefant (a class which Elefanträknaren turns into an Image:
import java.awt.*;
import java.util.*;
import javax.swing.ImageIcon;
public class Elefant extends Panel implements Runnable
     private int x, y; //Elefantens koordinater
     private int hälsa; //Elefantens hälsa
     private int RÖRELSESTEG = 10;//Antal pixlar elefanten ska röra sig i sidled
     private int DELAY;
     //Animation
     private Vector bilderna = new Vector();
     private Vector bilderna2 = new Vector();
     private int fas; //Delen av animationen som ska visas
     private boolean framåt;
     //Tråddelen
     private Thread tråd;
     public Elefant(int x, int y, int hastighet)
          this.x = x;
          this.y = y;
          DELAY = 1000 - hastighet;
          hälsa = 100;
          framåt = true;
          fas = 0; //Nollställ fasen
          //Få fram bildernas namn
          for( int i = 0; i <= 5; i++ )
               Image temp = new ImageIcon("Z:\\Projektet\\gamal\\Projektet\\Mappen\\mediat\\png\\jumbo" + i + ".png").getImage();
               bilderna.add(temp);
               Image temp2 = new ImageIcon("Z:\\Projektet\\gamal\\Projektet\\Mappen\\mediat\\png\\jumbo" + i + "r.png").getImage();
               bilderna2.add(temp2);
     //get-variabler
     public int getX() { return x; }
     public int getY() { return y; }
     //Kör igång tråden/ge elefanten liv
     public void startaTråd()
          if( tråd == null )
               tråd = new Thread(this); //Skapa tråden
               tråd.start(); //Kör igång
     //Rör elefanten i sidled
     private void rörelse()
          //Animering
          if( fas < 5 ) fas++;
          else     fas = 0;
          //Flytta ner elefanten när den når en av spelets kanter
          if( x >= 800 || x <= 10 ) y += 85;
          //Kontrollera riktning
          if( x >= 800 ) framåt = false;
          else if( x <= 10 ) framåt = true;
          //Positionering
          if( framåt ) x += RÖRELSESTEG;
          else x -= RÖRELSESTEG;
     //Hämtar den aktuella bilden, och returnerar den
     public Image getBild()
          Image temp;
          if( framåt ) temp = (Image) bilderna.get(fas);
          else temp = (Image) bilderna2.get(fas);
          return temp;
     /* Tråd-hantering */
     //Stoppa tråden/döda elefanten
     public void stoppaTråd()
          if( tråd != null )
               tråd.interrupt();
               tråd = null;
     //Körs när elefanten är vid liv
     public void run()
          while( tråd != null )
               rörelse();
               try
                    Thread.sleep(DELAY);
               catch(Exception e){}
}

Why class builder allows to develop abstract final class ? What is the use of such class in ABAP?

I am new to ABAP. I tried creating abstract class and found that class builder allows development of abstract final class. What is the use of such class in ABAP?

Hi,
Does not compile:
This one do:
Inheritance:
Regards.

What is the correct way to model an abstract base class/table?

I tried to model an abstract base class/table. For the parent table I used the "Forward Engineer Strategy" "Table per child" and I set on each child table the "Super Type" to the corresponding parent table. I did this for two parent tables and five child tables. This is the result:
https://lh5.googleusercontent.com/-1La98ulWOZg/T_2Hyock5-I/AAAAAAAAAoI/00qn5ukJCpI/s678/2012-07-11
But when I engineer the logical model into a physical model, the result is not as expected:
https://lh5.googleusercontent.com/-YfF_ocUa8bY/T_2H_YSqkyI/AAAAAAAAAoc/rNEYRnTFzU4/s617/2012-07-11
First the parent table "obj" should not be created. The table is correctly omitted, but the primary key of the parent table gets created. For me this is not logical. And even worse the primary key gets created twice with the same name, which results in a DDL generation error.
And second the primary key of the "attr" table does not get merged into the primary key of the child tables. This results into two individual unique constraints although I have expected to create only one with two attributes.
Is this a bug or is there another way to model this example correctly?

chriswalsh wrote:
The installer for Silverlight installed it as a seperate volume displayed on the desktop...
Likely that's not the app itself. When you download most Mac software, you are downloading a .dmg file (a disk image) - opening that (which may happen automatically) mounts a disk image on your desktop, and then you drag the app from that disk image to your Applications folder (or an installer runs).
After copying/installing the app, you Eject the disk image, then delete the .dmg file (from your Downloads folder, probably).

Generic interface in abstract super class

hello java folks!
i have a weird problem with a generics implementation of an interface which is implemented in an abstract class.
if i extend from this abstract class and try to override the method i get this compiler error:
cannot directly invoke abstract method...
but in my abstract super class this method is not implemented as abstract!
do i have an error in my understanding how to work with generics or is this a bug in javac?
(note: the message is trown by the eclipse ide, but i think it has someting to do with javac...)
thanks for every hint!
greetings daniel
examples:
public interface MyInterface <T extends Object> {
   public String testMe(T t);
public abstract class AbstractSuperClass<T extends AbstractSuperClass> implements MyInterface<T> {
   public String testMe(T o) {
      // do something with o...
      // now we have a String str
      return str;
public final class SubClass extends AbstractSuperClass<SubClass> {
   @Override
   public String testMe(SubClass o)
      return super.testMe(o);
}

Hi Wachtda,
Firstly, T extends Object is redundant as all classes implicitly extend the Object class.
Therefore :
public interface MyInterface <T> {
   public String testMe(T t);
}Secondly, abstract classes may have both abstract and non-abstract instance methods. Also, two methods, one abstract and one non-abstract, must have a different signature.
The following example will give a compile error because the methods share the same signature :
abstract class Test {
     public void sayHello() {
          System.out.println("Hello");
     abstract public void sayHello();
}Therefore, to make an interface method as abstract would simply block the possibility of implementing it.
BTW, you can do this :
abstract class Test {
     public void sayHello() {
          System.out.println("Hello");
     abstract public void sayHello(String name);
}Finally, there's no bug in javac.

Where to put methods in a abstract base class - subclasses system

Hi,
I’d like to ask a question on some basic design practice.
When there are methods which are common in some subclasses so I would like to “move them up” in the base abstract class, I would also like to make sure that the ADT concept of the base class itself is not broken. So I don’t want to have methods in the base class that are not general enough to be there. How to resolve this?
For example I create a base abstract class Vehicle. Then I create subclasses Plane and Tanker and realize that the startEnginge() method in them is the same and in order remove the duplicated code, I can put it in Vehicle. But later there may be Bicycle or Sled subclasses which don’t need startEngine().
In a broader sense, I would like to keep the Vehicle class as similar to the real word concept of vehicles as possible. And not evey vehicle have engine of course.
What is the solution?
Extending the class hierarchy by injecting another abstract class between the base and the subclasses? (e.g: VehicleWithEngine)
I suppose I can’t use Interfaces because I need to have the common implemenations as well.
Thanks for any comments in advance,
lemonboston
ps: I am a beginner and don't know the terminology, so if there are programming expression for the followings for example, I would be thankful if someone could help with this too:
- moving common methods up in the class hierarchy
- injecting a class in the hierarchy
- abstract base class - subclasses system

lemonboston wrote:
Hi,
I’d like to ask a question on some basic design practice.
When there are methods which are common in some subclasses so I would like to “move them up” in the base abstract class, I would also like to make sure that the ADT concept of the base class itself is not broken. So I don’t want to have methods in the base class that are not general enough to be there. How to resolve this?
You are talking about code.
Instead you need to talk about the design.
The base class represents conceptually a 'type' of something. That 'type' defines behavior. That behavior is what goes in the base class nothing else (in terms of design.)
If you have common functionality which does not fit into the definition (design) of the 'type' then you put it in another class and use (composition) that class in the sub class.
For example I create a base abstract class Vehicle. Then I create subclasses Plane and Tanker and realize that the startEnginge() method in them is the same and in order remove the duplicated code, I can put it in Vehicle. But later there may be Bicycle or Sled subclasses which don’t need startEngine(). No that is not how it works.
You have specific examples of some vehicles and then you need to manage those types generically. That is the first step.
Second step is then to determine what the exact 'type' is that you want to manage. And you use the requirements of the need to create the 'type'.
Then you look at the specific examples to determine how they will meet the needs of the type.
Thus if I have an application that must start the engines of all the vehicles in the city then I must have a vehicle class which has startEngine.
But if I have an application that manages vehicles as inventory (like a retail store) and then decide that because my examples both have engines that I might as well move it into the base class. In that case there is no 'need' for the application to manage starting vehicles. The fact that both have engines is irrelevant.
So looking back at your example you have stated functionality about your specific types but you have not stated anything about why your application needs to deal with that functionality generically.
Another way to think about it is that you do not put the shared functionality in the base because you can but rather because you must.

Are methods in the Graphics class Thread Safe

Can methods from the Graphics class (.e.g. drawImage(), drawString(), ect..) be called from any thread? In other words, can two threads that refer to the same Graphics object step on each other methods calls?
TIA,
DB
Edited by: Darth_Bane on Apr 27, 2009 1:44 PM

No,
They are GUI activities so you should call them from the Swing Thread ( Event Disptach Thread)
Now for the JComponent the following are thread safe:
repaint(), revalidate, invalidate which can be called from any thread.
Also the listener list can be modified from any thread addListenerXX or removeListenerXX where XX is ListenerType
Regards,
Alan Mehio
London, UK

Information about Graphics class

how will I be able to see the source code of the graphics class.

As far as I can see there's no ByteArray class in the standard API.
There are java.io.ByteArrayInputStream and java.io.ByteArrayOutputStream objects, and also there's java.util.BitSet.
The syntax for them is the same as for any other part of the language. You probably mean the API. The API is in fact well-documented, just like most of the API.
You don't need to import any package. You do need to import the classes or just refer to them with their full name (including package).
All these things are determined from reading the documentation.
Do you have any specific questions?

Abstract/ concrete class questions/problems

I am new to java and working on a abstract problem. I'm getting several errors. Here is the code I have so far for the abstract class. I commented out the super and it compiles but I'm not sure if it correct. I'm suppose to create a abstract base class Animal. Single constructor requires String to indicate type of animal which then is stored in an instance variable. I also have to add a few methods (describe(), move(), etc).
public abstract class Animal
     public Animal(String type)
          //super(type);
     public abstract String describe();
     public abstract String sound();
     public abstract String sleep();
     public abstract String move();
}

thanks for the replies. I modified my code but I have a few more errors I can't figure out. Can you browse the code and help point me in the right direction.
Here are the errors I get
cannot find symbol
symbol : constructor Cat(java.lang.String,java.lang.String)
location: class Cat
cannot find symbol
symbol : constructor Robin(java.lang.String)
location: class Robin
abstract base class:
public abstract class Animal
     String type;
     public Animal(String type)
       this.type = type;
     public abstract String describe();
     public abstract String sound();
     public abstract String sleep();
     public abstract String move();
}concrete class
public class Cat extends Animal
     private String name;
     protected String breed;
     public Cat()
       super("Cat");
     public String describe()
          return new String(",a breed of Cat called");
     public String sound()
          return new String("Meow");
     public String sleep()
          return new String("Kitty is having purfect dreams!");
     public String move()
          return new String("This little Kitty moves fast!");
}another abstract class
public abstract class Bird extends Animal
     protected String breed;
     public Bird()
       super("Bird");
     public abstract String move();
}here is the abstract test program itself
public class AbstractTest
     public static void main(String[] args)
          Cat cat = new Cat("Kitty", "Angora");
          Robin bird = new Robin("Rockin");
          System.out.println("Form the cat:   ");
          System.out.print("This is:     "); cat.describe();
          System.out.print("Sound:       "); cat.sound();
          System.out.print("Sleeping:    "); cat.sleep();
          System.out.print("Moving:      "); cat.move();
          System.out.println("\n");
          System.out.println("For the robin:     "); bird.describe();
          System.out.print("This is:             "); bird.sound();
          System.out.print("Sound:               "); bird.sleep();
          System.out.print("Moving:              "); bird.move();
          System.out.print("\n");
          System.out.println("nEnd of program.");
}

CDR-17066 RON cannot find java EWT graphics classes

Hello,
I am evaluating Oracle SCM. Everything's going great, except I am unable to use the Version History or Version Events. When I try, I get an error:
"CDR-17066: RON cannot find java EWT graphics classes"
The action it recommends is to check the registry or environment variable JVM_CLASSPATH_RON, and make sure it points to the ewt jar.
I found a jar called ewt3.jar in my oracle/jlib directory. There was no environmental variable called JVM_CLASSPATH_RON, so I created one and set it to that jar. But I'm still getting the same error.
Any help would be appreciated. Thank you.

Hi,
this error message is rather strange: I checked in our knwoledge base, but you seem to be the first one having this issue!
I had a look to my registry and indeed I couldn't find the variable JVM_CLASSPATH_RON.
I suspect that this variable was superseded by another one (JVM_CLASSPATH_DEFAULT_THIN_JDBC ?).
I checked for all variables including ewt and found the following:
. FORMS90_CLASSPATH (<Home>\jlib\ewt3.jar)
. FORMS90_BUILDER_CLASSPATH (<Home>\jlib\ewt3.jar)
. JVM_CLASSPATH_DEFAULT_THIN_JDBC (<Home>\jlib\ewt4.jar)
FORMS90_... variables are not used by the Version History and Version Event Viewers, but JVM_CLASSPATH_DEFAULT_THIN_JDBC is.
I removed the entry <Home>\jlib\ewt4.jar from JVM_CLASSPATH_DEFAULT_THIN_JDBC, and then I could reproduce your issue.
So could you check the content of this variable JVM_CLASSPATH_DEFAULT_THIN_JDBC?
It's located in HKEY_LOCAL_MACHINE\SOFTWARE\Oracle\HOMEx\REPADM61\DEFAULT_JVM_PARAMS_THIN_JDBC
Could you also check that file <Home>\jlib\ewt4.jar does exist on your machine?
Regards,
Didier.

Question about Abstract,Final Class

when we are using final keyword along with class definition .we are making that class final, means we can’t extend that class. The same thing happens when we make our constructors private. From usability perspective both are same ? or is there any difference?
Secondly accounting to java syntax a class can be either final or abstract and not both .Then why language specification doesn't impose any restriction on making abstract classes constructor private. We can create an Abstract class with private Constructor (Basically utility class with all methods are static) ,to make this class Singleton .This situation is equal to abstract final class ?
Thanks,
Paul.

EJP wrote:
when we are using final keyword along with class definition .we are making that class final, means we can’t extend that class. The same thing happens when we make our constructors private.No it doesn't.
Secondly accounting to java syntax a class can be either final or abstract and not both.Correct.
Then why language specification doesn't impose any restriction on making abstract classes constructor private.Why should it? That proposition doesn't follow from your previous sentence.I think OP is asking about this case
public abstract class WTF {
private WTF() {}
private WTF(...) {}
}where the class is abstract and all the c'tors are final. It's an abstract class that cannot be extended, much like a final abstract class would be if it were allowed. So, since purpose of abstract classes is to be extended, the OP seems to be asking, "Why can we, in this fashion, create an abstract class that cannot be extended?"
I don't know the answer to that, but I would guess that, while final is an explicit syntactical element for the purpose of making a class non-extensible, in the all-private-c'tors case, the non-extensibility is simply a side effect, and probably enough of a corner case that it wasn't worth the effort to explicitly forbid it in the spec.
I also think it's something not worth thinking much about. It was certainly not a key point of some grand design.

Color filling problem in fillarc() method of Graphics class

I draw a circle in a panel. The circle space is divided to more than one sectors.The sectors are filled to particular color using fillarc(int x, int y, int start_angle, int end_angle) method of java.awt.Graphics class.
When i fill the color, i faced a problem. That is i have seen the panel background Color in some pixels of thet arc spaces.
How will i fill the particular color in full arc spaces? How will i solve this problem?
Thanks for your advance reply.
Regards
Murali.R

import java.awt.*;
import java.awt.geom.*;
import javax.swing.*;
public class ArcFill extends JPanel {
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        int w = getWidth();
        int h = getHeight();
        double radius = Math.min(w,h)*7/16.0;
        double x = (w - 2*radius)/2;
        double y = (h - 2*radius)/2;
        Ellipse2D.Double circle = new Ellipse2D.Double(x,y,2*radius,2*radius);
        // Fill east sector with Arc2D.
        Rectangle r = circle.getBounds();
        double start = -45.0;
        double extent = 90.0;
        int type = Arc2D.PIE;
        Arc2D.Double arc = new Arc2D.Double(r, start, extent, type);
        g2.setPaint(Color.red);
        g2.fill(arc);
        // Fill south sector.
        arc.setAngleStart(-135.0);
        g2.setPaint(Color.green.darker());
        g2.fill(arc);
        arc.setAngleStart(-225);
        g2.setPaint(Color.blue);
        g2.fill(arc);
        arc.setAngleStart(-315);
        g2.setPaint(Color.orange);
        g2.fill(arc);
        // Draw circle and lines.
        g2.setPaint(Color.black);
        g2.draw(circle);
        double theta = -Math.PI/4;
        double cx = circle.getCenterX();
        double cy = circle.getCenterY();
        for(int j = 0; j < 4; j++) {
            x = cx + radius*Math.cos(theta);
            y = cy + radius*Math.sin(theta);
            g2.draw(new Line2D.Double(cx, cy, x, y));
            theta += Math.PI/2;
    public static void main(String[] args) {
        ArcFill panel = new ArcFill();
        panel.setPreferredSize(new Dimension(400,400));
        JOptionPane.showMessageDialog(null, panel, "", -1);
}

Anchor point used in drawImage() of Graphics class

Hi all,
This is sourab.I need to know about the concepts of anchor point used in drawImage() of Graphics class.We all know in drawImage() method has four co-ordinates.First one is for Image name,second one is for x coordinate ,third one is for y coordinate and the final one is for anchor point.Actually anchor point will place the image in the corresponding position.Now my doubt is what is the purpose of x,y coordinates.
Also i want some links to learn about this anchor point concepts.Can anyone provide solution to me ASAP.
Regards/Thanks,
Sourab

We all know in drawImage() method has four co-ordinates. [coördinates?]http://java.sun.com/javase/6/docs/api/java/awt/Graphics.html
Or 5 or 6 or 7 or 10 or 11. And if you include Graphics2D:
http://java.sun.com/javase/6/docs/api/java/awt/Graphics2D.html
There is second one taking 4 arguments, and one taking 3.

Abstract Entity classes with Collections

I trying to figure out a way to have a generics collection in a parent collection that can hold various entity types of the same super-class.
One thing I've tried was the following:
@Entity
public class ParentEnt implements Serializable {
    private static final long serialVersionUID = 1L;
    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long id;
    @Column
    private String parentName;
    @OneToMany(mappedBy="parentEnt")
    private Collection<ChildAbs> children;
    /* Methods removed */
@Entity
public abstract class ChildAbs implements java.io.Serializable {
    protected static final long serialVersionUID = 1L;
    @Id
    protected Long id;
    @ManyToOne
    protected ParentEnt parentEnt;
    /* Methods removed */
@Entity
public class ChildEnt extends ChildAbs implements Serializable {
    @Column
    protected String childName;
}but this is the error I get:
Exception [TOPLINK-30005] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.PersistenceUnitLoadingException
Exception Description: An exception was thrown while searching for persistence archives with ClassLoader: sun.misc.Launcher$AppClassLoader@11b86e7
Internal Exception: javax.persistence.PersistenceException: Exception [TOPLINK-28018] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.EntityManagerSetupException
Exception Description: predeploy for PersistenceUnit [testPU] failed.
Internal Exception: Exception [TOPLINK-7250] (Oracle TopLink Essentials - 2.0 (Build b58g-fcs (09/07/2007))): oracle.toplink.essentials.exceptions.ValidationException
Exception Description: [class test.ParentEnt] uses a non-entity [class test.ChildAbs] as target entity in the relationship attribute [private java.util.Collection test.ParentEnt.children].So, it looks like there is no way to have a generics collection for an abstract entity class. Is there another way to accomplish what I want using a generics collection?
Additionally, entity ChildEnt generates an error due to the abstract class' id property not carrying forward (see Abstract Entities: http://java.sun.com/javaee/5/docs/tutorial/doc/bnbqa.html#bnbqo)
Exception Description: Entity class [class testprintservices.ChildEnt] has no primary key specified. It should define either an @Id, @EmbeddedId or an @IdClass.Any input would be appreciated.

As far as my first question, I was trying to make my collection so it can hold various type of entity classes, but now that I think about it, it was a bad idea. For instance, being able to hold ChildEnt and ChildEnt2 in the same collection. If JPA did allow this, it might be possible to save the entities to the DB, but the reverse wouldn't be possible.
Ok, regarding my 2nd question: I don't understand why having it as @Entity wouldn't. The links (mine and yours) clearly shows that @Id is carried forward in the example they provide. Anyway, since I can't use the superclass in the collection, this is pointless. I'll use the suggested annotation.
Thanks.

Abstract Graphics class ???ques???

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