Empty Virtual Base Classes

Calls made by my code to virtual functions within a class hierarchy were ending up elsewhere in the hierarchy; adding a dummy data member to the hierarchy's empty virtual base class removed the problem. Apparently this is a known problem in the Sun Workshop 6 update 1 C++ 5.2 compiler with the above-mentioned workaround. The readme for patch 109508-03 indicates the following problem fix:
4309374 virtual table layout incorrect for empty virtual bases
Will this patch remove the misdirected calls to virtual functions or do I have to get the latest compiler release, which is supposed to remove the need for dummy data members in empty virtual base class?

Due to the fact that Java does not support multiple (implementation) inheritance, the diamon-shaped inheritance issue does not arise with Java, hence there is no need to distinguish between "plain" and "virtual" base class.
(FYI: "Virtual base class" is C++ lingo.)

Similar Messages

Flash Pro is ignoring changes to my base class when publishing / debugging

Hi,
I hope this will be in the correct section of the forum.
I've been working with Actionscript 3 since a while now although most of the time I've just done straightforward coding using Flash Develop.
This is the first time I'm building a more or less complex project in Flash Pro.
Here's a quick outline of how the project is structured.
There is a swf file which holds a large set of components. Things like Buttons, Sliders, complex List components, etc.
All of them are written from scratch not using any existing components (reason being project requirements).
As someone with a heavy programming background I've done as little as possible in the timeline / frames, most of my code lives in classes which are attached to the components I've created in Flash Pro.
These classes handle all the functionality. These classes then usually inherit from a base class where some basic functionality lies that I need across all components.
The components outlined above are all marked for export and lateron imported into other swf files where they are used.
So far so good, all that works like a charm.
Now here's the actual problem.
Today I needed to make changes to the base class to change some fundamental behaviour across all components that inherit from said base class.
The change in itself was fairly simple.
However, every time I now try to debug or publish it will completely ignore any change I've made and use the previous version of my base class?
I can go as far as completely emptying my base class and every time I debug or publish it will do so using the base class from before. I can see at runtime that it is the previous version because of the behaviour of the inherited components.
That's what I don't get. Where does it take that version from? I tried clearing the publish cash, to no avail.
I can pace tracers, nothing. If I add code to the base class and make an error it will complain so when I try to debug or publish but once fixed, it won't use any of it. It's still behaving as if it's using a previous version.
What makes all this even weirder is that if I take that new code and place it into another class and inherit my components from this one, then the build will use that new verison with the new code. If I switch back to the old base class with exactly the same code inside it will ignore it again and once more behave as if its an older version of it.
I've been looking around the net but simply can't find what this could be caused by.
Now, sure, I could simply use a new class and inherit all my components from a different base class but that's rather unpractical.
What I would like to know is, why does Flash Pro ignore any changes to this class? Is this an issue with how I inherit my component classes from a base class? I kind of doubt it because it has been working like a charm before.
Could this be a Flash Pro issue?
This is also not the first time I've come across this problem. The previous time however, after much tinkering, it went away. Today, it didn't. I would really like to get to the bottom of this.
FYI: I'm running Flash Pro CC. I design my components in Flash Pro and do all my coding in Flash Develop.
Any help would be greatly appreciated.

Hmm, my classes live in a subfolder of where my fla files live. (This sub folder again is divided into further folders to organise the code)
I haven't actually setup any class paths. (default class path is set to .)
If I set the default class path to the folder where my code lives I get a ton of errors telling my that my package names don't reflect the location of my files.
edit: That was a mistake on my side. I've set the class path to where my code lives and made sure the package names still match up.
Unfortunately it still ignores my base class (which lives in a sub folder of the defined class path)

Warning :: Derived class hides the base class virtual function

We are porting from CC5.3 to CC5.8 compiler with Sun Studio one compiler. After plenty of hurdles we are in the final stage of removing the warning messages... Amoung the plenty the following one is very common and in different files. Why am I getting this error in 5.8 and not in 5.3 compiler....
Warning: derived_Object::markRead Hides the virtual function base_Object::markRead(ut_SourceCodeLocation&) const in a virtual base
From this it is easily understandable that the base class mark read was hidden by derived class markRead... when we drive and override the derived class function.... It is all over the place....
Thank you,
Saravanan Kannan
//public: using xx_Object :: markRead;
virtual void markRead() const;

The Sun C++ FAQ discusses the warning message:
http://developers.sun.com/prodtech/cc/documentation/ss11/mr/READMEs/c++_faq.html#Coding1
Notice that warnings are not necessarily errors. But I applaud your desire to fix the code so that it generates no warnings. I wish more of our customers could be persuaded to do the same. :-)
C++ 5.3 issues this warning, by the way. Example:
struct B { virtual int foo(int); };
struct D : B { virtual int foo(double); }; // line 2
D d;
line 2: Warning: D::foo hides the virtual function B::foo(int).
If for your particular code you do not see a warning with C++ 5.3, it would be due to a bug in C++ 5.3 that was later fixed.

SW6U2 (C++) wrong code with empty base class

Consider this program:
#include <assert.h>
#include <new>
struct Base1
int i;
struct Base2
Base2()
struct Derived : public Base1, public Base2
int main( int, char** )
int buf[2] = { 0x7F7F7F7F, 0x7F7F7F7F };
assert( sizeof( Derived ) == 4 );
new (buf) Derived;
assert( buf[1] == 0x7F7F7F7F ); // <- failure
The second assert fails, because the second (empty) base class Base2 is placed at offset 4 of Derived. But when the custom Base2 constructor runs it makes implicit something like
memset( this, 0, sizeof( Base2) );
sizeof( empty class ) is 1 and the offset of Base2 is 4. Effect is that the constructor writes to memory that is not owned by the whole object.
This can produce some subtile memory errors.
Joerg
p.s. What is the right way to submit and view bugs for this C++ compiler?

The forum posting software eats some C++ code. To get all the code displayed, you must use "code" brackets, and leave a space after each "<" and before each ">".
I assume your two include statements are these:#include < assert.h >
#include < new > and that the rest of the code displayed correctly.
Under those assumptions, I cannot duplicate the bug using the initial release of C++ 5.3, nor with the latest patch. Please be sure the code you post actually shows the problem, and use the "preview" button to see that the code displays correctly.
If you still see the bug with the code you posted, please run this command
CC -V -c foobar.cc
and tell me what output you get. The file foobar.cc does not need to exist.

How to deserialize xml with structure of abitrary nested layers of base class?

let say i want to represent arithmetic expression using xml:
<?xml version="1.0" encoding="utf-8" ?>
<expr>
<add>
<num>10</num>
<num>20</num>
</add>
</expr>
and here is my classes to represent this:
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace Test
public abstract class Evaluable
public abstract int Eval();
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;
namespace Test
[Serializable]
[XmlRoot("expr")]
public class Expr
[XmlElement]
public Evaluable Evaluable { get; set; }
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;
namespace Test
[Serializable]
[XmlRoot("add")]
[XmlType("add")]
public class Add : Evaluable
[XmlElement]
public List<Evaluable> Elems { get; set; }
public override int Eval()
return Elems.Select(e => e.Eval()).Sum();
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Xml.Serialization;
namespace Test
[Serializable]
[XmlRoot("num")]
[XmlType("num")]
public class Num : Evaluable
[XmlText]
public int Val { get; set; }
public override int Eval()
return Val;
but it doesn't work, and it's reasonable, since Serializer doesn't know any thing about the subclass. but how to make it work?
here is my deserialization code:
var serializer = new XmlSerializer(typeof(Expr), new[] { typeof(Add), typeof(Num) });
Expr expr = null;
using (var file = new StreamReader("expr.xml"))
expr = serializer.Deserialize(file) as Expr;

I think what you want is to set the XmlElement attribute on the container (Elems).
It can be done if the deserializer can be made aware of all the potential subclasses of the base class. It's ok to put multiple XmlElement attributes on the container to let the deserializer know about the various subclasses it can deserialize.
I don't think there's a way to tell the XmlSerializer externally about new types. I could be wrong. [If someone shows me how to do that, I'd sure appreciate it!] [WORKAROUND: A potential workaround
is to create a class that contains all the potential children including the class itself and serialize that. Seems a little like cheating.]
Here is a complete example:
[Serializable]
public class Foo
[XmlAttribute( "name" )]
public string name;
[XmlElement( "Foo", Type = typeof( Foo ) )]
[XmlElement( "Bar", Type = typeof( Bar ) )]
public List<Foo> children = new List<Foo>();
public void Dump( int level )
ShowProperties( level );
foreach( var f in children ) {
f.Dump( level + 1 );
protected virtual void ShowProperties( int level )
Console.WriteLine( "{0}{1}", new string(' ', level * 4 ), name );
[Serializable]
public class Bar : Foo
public string stuff;
protected override void ShowProperties( int level )
base.ShowProperties( level );
Console.WriteLine( "{0}{1}", new string(' ', level * 4 ), stuff );
class Program
static void Main( string[] args )
// <Foo name="A">
// <Bar name="B">
// <Foo name="D" />
// <stuff>B's Stuff</stuff>
// </Bar>
// <Bar name="C">
// <stuff>C's Stuff</stuff>
// </Bar>
// </Foo>
// A
// B
// B's Stuff
// D
// C
// C's Stuff
Foo a = new Foo() { name = "A" };
Bar b = new Bar() { name = "B", stuff="B's Stuff" };
Bar c = new Bar() { name = "C", stuff="C's Stuff" };
Foo d = new Foo() { name = "D" };
a.children.Add( b );
a.children.Add( c );
b.children.Add( d );
XmlSerializer xs = new XmlSerializer( typeof( Foo ) );
// There:
XmlSerializerNamespaces ns = new XmlSerializerNamespaces( new[] { XmlQualifiedName.Empty } );
StringBuilder sb = new StringBuilder();
using( XmlWriter xw = XmlWriter.Create( sb, new XmlWriterSettings() {
OmitXmlDeclaration = true,
Indent = true
xs.Serialize( xw, a, ns );
Console.WriteLine( sb.ToString() );
// And Back Again:
using( StringReader sr = new StringReader( sb.ToString() ) )
Foo root = (Foo)xs.Deserialize( sr );
root.Dump( 0 );

Inheritance problem: base class does not see stage instances

I'm writing a series of Search windows for an application. I create the FLA files on the stage, each has 3 simple buttons: next_btn, prev_btn, and close_btn. Those all have event listeners which call findNext(), findPrev() and closeWin() respectively. Each search window looks for different things, some with a text box and some with a combo, etc.
So I have a base class com.search that extends Sprite and adds the eventListeners at startup (actually, on addedToStage). Like this:
function isAddedToStage(evt:Event){
   next_btn.addEventListener("click",findNext);
   prev_btn.addEventListener("click",findPrev);
   close_btn.addEventListener("click",closeWin);
Then I write the appropriate find functions in each derived class.
For example, I have
package com {
     import com.search;
     class searchText extends search {
In my FLA file, I set the class to com.searchText.
But when I compile and run the window, I get runtime errors:
ReferenceError: Error #1065: Variable next_btn is not defined.
at com::search()
at com::searchtext()
If I add the event listeners in the derived class rather than the base, it works fine. But that seems to defeat the purpose of inheritance, plus it infers that I won't be able to derive new classes/swfs from those derived classes.
So the question is, how does one reference objects created on the stage from a base class of that document's class?

Found it. After messing around with trying dynamic classes and overriden functions that returned the desired button (that worked, but was ugly.)
Simply and silly once you know how.
You have to explicitly reference the stage objects (or any newly declared methods or properties) in the derived class as members of "this" in the base class - so:
class Search {
function isAddedToStage(evt:Event){
   this.next_btn.addEventListener("click",this.findNext);
   this.prev_btn.addEventListener("click",this.findPrev);
   this.close_btn.addEventListener("click",closeWin);
function closeWin(e:Event){
and then create the buttons on stage in the FLA using the derived class.
You can also declare the event handling functions in the base class as empty functions and then override them in the derived classes. Or fill in the functions in the base class to throw a runtime error, and then override - that's as close to an abstract class as you can get, I think.

How to call a Derived call fucntion with a base class object ?

Hi all
i am working on a JNI interface to Java, and in the process of simulating a C++ behaviour in java
so i need some help form you people, in this regard.
here is a c++ code, i need a equivalent fucntionality in java , to put it one word, the question is
how to implement the dynamic_cast functionality in java, as java also has virtual fucntions, i think
this should be possible, if it is not, what is the alternative
class Base
public:
     Base()
     ~Base()
     virtual void F1()
          cout<<"The BASE::F1() is called"<<endl;
     virtual void F2()
          cout<<"The BASE::F2() is called"<<endl;
class Derived : public Base
public:
     Derived()
     ~Derived()
     virtual void F3()
          cout<<"The Derived::F3() is called"<<endl;
     virtual void F4()
          cout<<"The Derived::F4() is called"<<endl;
Base * GetDerived()
     return new Derived();
int _tmain(int argc, _TCHAR* argv[])
     Base *ptr = NULL;
                ptr = GetDerived();
     Derived *dPtr = dynamic_cast<Derived *>(ptr);
                dPtr->F3();
}regards
pradish

Just to clarify a point that I consider important--the distinction between references and objects:
Your subject is: How to call a Derived call fucntion with a base class object ? The answer to that is: You cannot. It is completely impossible in Java. If you have a base class object, the derivced class' methods are not present. On the other hand, if you have a compile-time reference of the parent type, but at runtime it happens to point to an instance of the derived class, then, as pointed out, you can cast the reference. (Note that casting does not apply to objects.)

AS3: How to create one base class for classes loaded in multiple swfs?

Our application have 3 different modules and all use
fscommand and ExternalInterface alot. Now the problem is we are
combining all those modules, but they all will reside in different
swfs. Is there any way that they extend to same base class and its
static members have only one instance accessible by all
three?

Hi,
You can achieve this via Workshop 9.2 by using the exported Ant script for your project as follows:
-Ensure that all Jars needed to resolve com.bea.p13n.property.EntityPropertyManager (this particular class is found in weblogic92/common/p13n/lib/p13n_ejb.jar) and all referenced classes are added to the Java build path for your WebLogic EJB project (Properties->Java Build Path->Libraries)
-Export the "Workshop Ant Script" for your WebLogic EJB project (File->Export->Workshop Ant Script); this will generate a "build.xml" Ant script under your project root directory.
-Edit this default build script as follows: in the call to the "ejbgen" task within the "build" target, add the attribute: propertyFile="ejbgen.properties"
-Create a file "ejbgen.properties" under the root of your WebLogic EJB project and add the following entry:
YourSessionBeanClassName.remote.baseClass=com.bea.p13n.property.EntityPropertyManager
-Add a "<path refid="java.classpath"/>" within the "<classpath>" for the "java" task element that calls "weblogic.ejbc" (this will ensure that the p13n classes are resolved by EJBC)
Follow the instructions for executing the Ant build script found here: http://edocs.bea.com/workshop/docs92/ws_platform/ideuserguide/conUseCustomAntBuild.html
For more information on the EJBGen property file support, see: http://e-docs.bea.com/wls/docs92/ejb/EJBGen_reference.html

Class override, how to create the child class and then the base class

I started to write a program for a smart DMM, the problem is every version of the DMM the company change the communication commend.
My idea is to write a child class for every DMM version and every SubVI of the child will override the base class SubVI.
My problem is, i want first to create one child class and after i will see every thing is work, start to create the base class. that way i will see if am thinking the right way.
My question is
How can i create a child class and then create the base class and configure the SubVi of the child class to be Override of the base class?
I tried to search in the property of the class but i didn't see nothing.
Thanks
Solved!
Go to Solution.

This can be done and I've done it on occasion.
You simply create the base class with the dynamic dispatch methods you require (connector panes need to be identical to thos of the child class).
Then set the inheritance of the class to inherit from this base class. If your method is defined as a dynamic dispatch method in the parent, you'll most likely now have some errors (unless your child method was already DD in which case you might just be OK already).
To change the inheritance of a class, right-click the properties of the class in your project and select properties. I believe the ineritance tree is at the lower end of the properties. Click on the "change inheritance" (or something similar) to choose the class from which you now wish to inherit.
Say hello to my little friend.
RFC 2323 FHE-Compliant

How to specify a base class for Remote Interface in Workshop 9.2? -- URGENT

Hi,
I am trying to create a UUP EJB in WebLogic 9.2 workshop. I am using @FileGeneration to create my home & remote interfaces. And the generated remote interface is extending javax.ejb.EJBObject;I want my remote interface to extend com.bea.p13n.property.EntityPropertyManager which in turn implements javax.ejb.EJBObject. Can someone tell how i can do it in Workshop?.
I came across Predefined Variable: remote.baseClass and as per docume
ntation..."If specified, the value of this variable will be used as the base class for all generated remote classes. Where i should specify it?. @FileGeneration does nt have any option for it. Any help is grtly appreciated.
Following are my code snippets:
IMPL Class
@FileGeneration(remoteClass = Constants.Bool.TRUE,remoteHome = Constants.Bool.TRUE, localClass = Constants.Bool.FALSE, localHome = Constants.Bool.FALSE,remoteClassName = "MyEntityPropertyManager",remoteHomeName = "MyEntityPropertyManagerHome")
public class MyEntityPropertyManagerImpl extends GenericSessionBean implements
SessionBean {
//code
}

This question was posted to both the bea.workshop.developer.general and weblogic.developer.interest.workshop (I had replied to the later on 10/19); after seeing an identical question today on this list want to include a reference to that reply here:
http://forums.bea.com/bea/message.jspa?messageID=600044925&tstart=0
-Rob

How to expose and code the event handlers of a base class?

I have created a class that inherits NumericUpDown. When I instantiate an object from that class, I can make it visible and have it appear on my form just like any other NUD. How can I get that instantiated object to expose the event handlers of its base
class, the NUD in this case, so that, for example, I can tell the client what action to take when the value of the instantiated object changes?
Thanks for your help.

I am not sure exactly what you mean. Are you adding your NUD controls to the Form at design time from the toolbox or adding them in code at run time? If you are adding them to the form from the toolbox then you access the events the same way
you would a standart NUD control. If it is at runtime and you have a fixed amount of them you are going to add then you can declare them Class Scoped using the
WithEvents keyword which will let you access all their events.
Public Class Form1
Private WithEvents Nud1 As New NUD
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Me.Controls.Add(Nud1)
End Sub
Private Sub Nud1_ValueChanged(ByVal sender As Object, ByVal e As System.EventArgs) Handles Nud1.ValueChanged
Me.Text = Nud1.Value.ToString
End Sub
End Class
Public Class NUD
Inherits NumericUpDown
'Your custom code to make it work how you want...
End Class
If this is not what you are doing then you may need to explain a bit more and show the code you are using so we understand better.
If you say it can`t be done then i`ll try it

Error with instance variable and constructor of base class

I am getting the error on the following statement "protected Point apoint" of by base class. What is causing this problem? See my code:
package Shapes;
public abstract class Shapes
     protected Point apoint; / ****error at this line****/
     public void move(double xdelta, double ydelta)
          apoint.x += xdelta;
          apoint.y += ydelta;
public abstract void distance();
public abstract void show();
public String toString()
return "\nThe starting point is at coordinates ("+x+","+y+")";
package Shapes;
public class Lines extends Shapes
protected Point start;
protected Point end;
     protected double x;
     protected double y;
     double delta;
     public Lines( final Point apoint, final Point bpoint)
start.x = apoint.x;
          start.y = apoint.y;
          end.x = bpoint.x;
          end.y = bpoint.y;
public Lines(double xstart, double ystart, double xend, double yend)
this.xstart = xstart;
          this.ystart = ystart;
          this.xend = xend;
          this.yend = yend;
     public Lines(double x, double y)
          this.x = x;
          this.y = y;
               public void distance(final Lines start, final Lines end)
                    delta = abs(Math.sqrt (super.x - start.x) * (super.x - end.x) +
                    (super.y - start.y) * (super.y - end.y));
               Lines move(Point start, double delta)
                    end.x += delta;
                    end.y += delta;
                    return new Point(end);
public Lines show()
g.drawLine( start.x, start.y, end.x, end.y);
public String toString()
return super.toString()+ "\n moved distance is("
               + start + ") : (" + end + ")"
               +" \n to position(" + start + " ) : (" + end + ")";
package Shapes;
public class Rectangle extends Lines
     double delta;
public Rectangle (Point top_lft_pt, Point bottom_rght_pt)
super(top_lft_pt, bottom_rght_pt);
public Rectangle(double x_top_lft, double y_top_lft, double x_bottom_rght, double y_bottom_rght)
super(x_top_lft, y_top_lft, x_bottom_rght, y_bottom_rght);
     public Rectantgle is_it_diagonal()
          if(top_lft.x > bottom_rght.x && bottom_rght.x < top_lft.x)
               System.out.println("Point are Not Diagonal");
               public void distance(double delta)
                    delta = abs(Math.sqrt (top_lft.x - bottom_rght.x) * (top_lft.x - botton_rght.x) +
                    (top_lft.y - bottom_rght.y) * (top_lft.y - bottom_rght.y));
               public Rectangle move(final Point top_lft_pt, double delta)
                    bottom_rght.x += delta;
                    bottom_rght.y += delta;
                    return new Point(bottom_rght_pt);
               public void get_top_rght_coords()
                    Point top_rght = new Point();
                    top_rght.x = bottom_rght.x;
                    top_rght.y = top_lft.y;
               public void get_bottom_left_coords()
                    Point bottom_lft = new Point();
                    bottom_lft.x = top_lft.x;
                    bottom_lft.y = bottom_rght.y;
     public Rectangle show()
                    g.drawLine(top_lft.x, top_lft.y, top_rght_x, top_rght_y);
                    g.drawLine(bottom_lft.x, bottom_lft.y, bottom_rght.x, bottom_rght.y);
                    g.drawLine(top_lft.x, top_lft.y, bottom_lft.x, bottom_lft.y);
                    g.drawLine(top_rght.x, top_rght.y, bottom_rght.x, bottom_rght.y);
package Shapes;
public class Circles extends Lines
protected double radius;
     public double delta;
     protected Point center;
public Circles(double x, double y, double radians)
super(x, y);
          radius = radians;
     public Circles(Point acenter)
          center.x = acenter.x;
          center.y = acenter.y;
public void distance()
delta = abs(Math.sqrt(super.x - x) * (super.x - x) + (super.y - y) * (super.y -y));
     public Circles move(final Point Circles, double delta)
          return new Point(Circles);
public void show()
g.drawOval(Circles.x, Circles.y, radius, radius);
package Shapes;
import java .math .*;
import java.util .Random ;
public class ShapesDriver
Shapes[] aShape = new Shapes[10];
static double range = 101.0;
static Random r1 = new Random();
public static void main(String [] args)
double[][] coords = new double[10][10];
double[] radians = new double [10];
Shapes anyShape = {
new Circles(radians),
new Lines(coords),
new Rectangle(coords)
Shapes aShape; /***error at this line***/
          for(int i = 1; i <= coords.length; i++)
for(int j = 1; j <= coords.length; j++)
                                                  coords[i][j] = r1.nextDouble () * range;
                                                  radians[j] = r1.nextDouble () * range;
aShape[i] = anyShape[r1.nextInt(aShape.length)];
System.exit(1);

Thanks for your help with this problem. Now I have another problem that I am having a hard time figuring out. My program is using inheritance and polymorphism. I trying to use only one version of methods in the superclass points which extends the shapes class which is the abstract superclass vs. repeating the implementation of the methods (move, show, etc.) in each of the subclasses. The error I am getting is this "declare the class abstract, or implement abstract member 'Point Shapes.move()'. As you see, move is declared abstract and of type point in the Shapes superclass and it's behavior is implemented in the subclass Points extending Shapes. The other subclasses, circle, rectangle and lines will invoke the move method from Points and return a new point object. Why I am I getting the error to declare or implement move when the implementation is in Point?
Below is code, please help?
import java .awt .Point ;
public class ShapesDriver
     public static void main(String args[])
          int count = 0;
          int choice;
          Point start = null;
          Point end = null;
          System.out .println(" 1 i am here");
          start = new Point((int)(Math.random()* 10.0), (int)(Math.random()* 10.0));
          end = new Point((int)(Math.random()* 10.0), (int)(Math.random()* 10.0));
     System.out .println(" 2 i am here");
     System.out.println (start);
     System.out.println(end);
     for(int i = 0; i <= count; i++)
          System.out .println(" 3 i am here");
          choice = (int)(4.0 * Math.random());
          System.out .println(" 4 i am here");
          System.out.println (choice);
     switch(choice)
          case 0: //Lines
          System.out .println(" 5 i am here");
          Lines apoint = new Lines((int)(Math.random()* 10.0), (int)(Math.random()* 10.0),
                              (int)(Math.random()* 10.0), (int)(Math.random()* 10.0));
          Point coords = new Point((int)(Math.random()* 10.0),
                         (int)(Math.random()* 10.0));
          new Point((int)(Math.random()* 10.0),
                         (int)(Math.random()* 10.0));
          break;
          case 1: //Circles
          System.out .println(" 6 i am here");
          Circles center = new Circles((double)(Math.random()* 10.0),
          (double)(Math.random()* 10.0), (double)(Math.random()* 10.0),
          (double)(Math.random()* 10.0),(double)(Math.random()* 10.0));
          Circles centerpt = new Circles((int)(Math.random()* 10.0),
          (int)(Math.random()* 10.0), (int)(Math.random()* 10.0),
          (int)(Math.random()* 10.0), (double)(Math.random()* 10.0));
     break;
          case 2: //Rectangles
     System.out .println(" 7 i am here");
          Rectangle top_lft_pt = new Rectangle ((double)(Math.random()* 10.0),
                         (double)(Math.random()* 10.0), (double)(Math.random()* 10.0),
                         (double)(Math.random()* 10.0), (double)(Math.random()* 10.0),
                         (double)(Math.random()* 10.0));
          Rectangle bottom_rgt_pt = new Rectangle ((double)(Math.random()* 10.0),
               (double)(Math.random()* 10.0), (int)(Math.random()* 10.0),
                         (int)(Math.random()* 10.0), (int)(Math.random()* 10.0),
                         (int)(Math.random()* 10.0));
     break;
     default:
     System.out .println(" 9 i am here");
     System.out.println("\nInvalid shape choice =" + choice);
     System.exit(0);
     break;
     try
               System.in.read();
               catch(java.io.IOException ioe)
import java .awt .Point ;
public abstract class Shapes
     private String shape;
     public Shapes(String ashape)
          shape = new String(ashape);
     public abstract Point move();
     public double distance()
          return 0.0;
     public abstract void show();
     public String toString()
          return "\nThis shape is a" + shape;
import java .awt .Point ;
public class Rectangle extends Points
     protected Point top_lft;
     protected Point top_rgt;
     protected Point bottom_lft;
     protected double top_lft_x;
     protected double top_lft_y;
     protected double bottom_rgt_x;
     protected double bottom_rgt_y;
     protected Point bottom_rgt;
     protected double delta = 0;
     protected String shape = "Rectangle";
     public Rectangle(double x, double y, double top_lft_x,
                         double top_lft_y, double bottom_rgt_x,
                         double bottom_rgt_y)
          super(x, y);
          top_lft_x = top_lft_x;
          top_lft_y = top_lft_y;
          bottom_rgt_x = bottom_rgt_x;
          bottom_rgt_y = bottom_rgt_y;
     public Rectangle( double x, double y, Point bottom_rgt, Point top_lft)
          super(x, y);
          bottom_rgt_x = bottom_rgt.x;
          bottom_rgt_y = bottom_rgt.y;
          top_lft_x = top_lft.x;
          top_lft_y = top_lft.y;
     public String toString()
          return super.toString() + " coordinates top left= " + top_lft_x + "," + top_lft_y + "and bottom right" +
               bottom_rgt_x + "," + bottom_rgt_y + ")";
     public void is_it_diagonal()
          if(top_lft_x < bottom_rgt_x && bottom_rgt_x > top_lft_x)
               System.out.println("Points are Not Diagonal");
          public double distance()
               distance ();
               return delta;
          public Point move(Point top_lft)
               move();
               bottom_rgt_x += delta;
               bottom_rgt_y += delta;
               return top_lft;
          public void get_other_coords()
               top_rgt.x = bottom_rgt.x;
          top_rgt.y = top_lft.y;
               bottom_lft.x = top_lft.x;
               bottom_lft.y = bottom_rgt.y;
          public void show()
               super.show();
               System.out.println("new coords are :");
               System.out .println ("(" + top_lft_x + "," + top_lft_y + ")");
               System.out .println ("top right(" + top_rgt + ")");
               System.out .println ("(" + bottom_rgt_x + "," + bottom_rgt_y + ")");
               System.out .println ("bottom right(" + bottom_rgt + ")");
import java .awt .Point ;
public class Points extends Shapes
     protected double delta = 0.0;
     protected double x;
     protected double y;
     protected String ashape = "Points";
     public Points( double x, double y)
          super("Points");
          x = x;
          y = y;
     public Points( Point start)
          super("Points");
          x = start.x;
          y = start.y;
     public String toString()
          return super.toString() + "References coordinates(" + x + y + ")";
     public double distance(double x1, double y1 )
          return delta =(Math.sqrt(x - x1) * (x - x1) + (y - y1) *
          (y - y1));
     public Point move(Point pts)
          pts.x += delta;
          pts.y += delta;
          return pts;
     public void show()
          System.out.println("This shape is a" + ashape + "(" +
                              "(" + x+ "," + y + ")");
import java .awt .Point ;
public class Lines extends Points
     double delta = 0;
     protected double x;
     protected double y;
     protected String ashape = "Lines";
     public Lines( double x1, double y1, double x, double y)
          super(x1,y1);
          x = x;
          y = y;
     public Lines(Point start, Point end)
          super(start);
          x = end.x;
          y = end.y;
     public String toString(Point end)
          return super.toString() + "line points = (" + x + "," + y +
               "(" + end + ")";
     public double distance()
          distance ();
          return delta;
     public Point move(Point lines)
          move ();
          return lines;
     public void show()
          System.out.println("This shape is a" + ashape + "(" +
                              "(" + x + "," + y + ")");
import java .awt .Point ;
public class Circles extends Points
protected double radius;
protected double xcenter;
protected double ycenter;
protected String ashape = "Circle";
     public Circles( double x, double y, double cx, double cy, double radians)
          super(x, y);
          xcenter = cx;
          ycenter = cy;
          radius = radians;
     public Circles( Point acenter, Point ref, double radians)
          super(ref);
          xcenter = acenter.x;
          ycenter = acenter.y;
          radius = radians;
     public String toString(Point ref)
          return super.toString() + " reference points (" +
               ref + ")" +
               "center coordinates (" + xcenter + "," + ycenter + ")";
          public double distance(Point ref)
               return (Math.sqrt(ref.x - xcenter) * (ref.x - xcenter)
                         + (ref.y - ycenter) *
          (ref.y - ycenter));
          public Point move(Point center)
               move();
               return center;
          public void show()
               System.out.println("This shape is a" + ashape + "(" +
                              "(" + xcenter + "," + ycenter + ")");

How to call derived class to base class

Hello everybody,
I create a GUi application in java swing. Now i want to navigate between the screen but the timing between the screen is very slow bcoz i imported the class from package to another package. Now i want to extends one package to another package to reduce the navigation time but it saying error bcoz i cant able to call my derived class to base class. if anyone know the answer for this please answer this immediately.
If any other method is there to optimise the navigation time please tell me
by
(kamal)

Sorry, I've got major difficulties understanding your query:
I create a GUi application in java
ication in java swing. ok
Now i want to navigate between
the screenwhat? switch screens? display a different dialog?
but the timing between the screen is very
slowtiming? do you mean the time it takes to display a different dialog?
bcoz i imported the class from package to
another package.how did you come to the conclusion that that is the reason for the slowness? Did you do any profiling or is this just guess-work?

Set fields of derived class in base class constructor via reflection?

Does the Java Language Specification explicitly allow setting of fields of a derived class from within the base class' constructor via reflection? The following test case runs green, but I would really like to know if this Java code is compatible among different VM implementations.
Many thanks for your feedback!
Norman
public class DerivedClassReflectionWorksInBaseClassConstructorTest extends TestCase {
abstract static class A {
    A() {
        try {
            getClass().getDeclaredField("x").setInt(this, 42);
        } catch (Exception e) {
            throw new RuntimeException(e);
static class B extends A {
    int x;
    B() {
    B(int x) {
        this.x = x;
public void testThatItWorks() {
    assertEquals(42, new B().x);
    assertEquals(99, new B(99).x);
}

why not just put a method in the superclass that the subclasses can call to initialize the subclass member variable?In derived classes (which are plug-ins), clients can use a field annotation which provides some parameter metadata such as validators and the default value. The framework must set the default value of fields, before the class' initializer or constructors are called. If the framework would do this after derived class' initializer or constructors are called, they would be overwritten:
Framework:
public abstract class Operator {
    public abstract void initialize();
}Plug-In:
public class SomeOperator extends Operator {
    @Parameter(defaultValue="42", interval="[0,100)")
    double threshold;
    @Parameter(defaultValue="C", valueSet="A,B,C")
    String mode;
    public void setThreshold(double threshold) {this.threshold = threshold;}
    public void setMode(String mode) {this.mode = mode;}
    // called by the framework after default values have been set
    public void initialize() {
}On the other hand, the default values and other metadata are also used to create GUIs and XML I/O for the derived operator class, without having it instantiated. So we cannot use the initial instance field values for that, because we don't have an instance.

Reflection: attributes from the base class

Is there a way to get the attributes from the base class of a derived class via reflection? I only found methods to get the attributes from the derived class.
Example:
class A
int a = 4;
class B extends A
int b = 5;
Object unknown = new B();
Code/Idea to get all attributes from baseclass A using unknown (here: a=4)?

Thank you all for your hints. The mistake I make, was to use the baseclass, and not the derived class for getting the attributes. By using an extra parameter of type class I got all attributes in their context.
   private StringBuffer getDump(Object obj, Class cl)
         dmp.append(cl.getName() + " {\n");
         Field[] attribute = cl.getDeclaredFields();             <--- only the fields of the current class
         for (int j = 0; j < attribute.length; j++)
            attribute[j].setAccessible(true);
            try
               if (attribute[j].getType().isPrimitive() || attribute[j].getType() == String.class)
                  dmp.append(attribute[j].getName() + "=" + attribute[j].get(obj) + "\n");
               else
                  if (((attribute[j].getModifiers() & Modifier.STATIC) != Modifier.STATIC) &&
                      (attribute[j].getType().getName().startsWith("java.lang") == false) &&
                      ((attribute[j].getModifiers() & Modifier.FINAL) != Modifier.FINAL))
                     dmp.append(getDump(attribute[j].get(obj), attribute[j].get(obj).getClass())); <- recursive call
            catch (IllegalAccessException ex)
               ex.printStackTrace();
         dmp.append("}");
      return dmp;
   }

Empty Virtual Base Classes

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