Synchronization In Base Class Method

I have a base class that has a synchronized method. Therefore, for example:
class TheBaseClass {
public synchronized doSomething() {
// do something
class A extends TheBaseClass {
class B extends TheBaseClass {
}If I instantiate two new classes, new A() and new B(), and call doSomething() in each of them, is the lock shared between the two of them? Or do both objects get their own object lock? (I assume this is the case but I want to double check).
Michael

Since a synchronized instance method syncs on the instance on which its called, each instance in your example is locked independently of the other. Furthermore, this: A a1 = new A();
A a2 = new A();
B b1 = new B();
B b2 = new B();
TheBaseClass a3 = new A();
TheBaseClass b3 = new B();leads to 6 distinct locks, and calling doSomething on any of those objects does not obtain a lock for any of the others.

Similar Messages

Need to restrict base classes method to be accessed by child class object

class Sample
public void setValue(String sval)
System.out.println("sValue is : "+sval);
class ChildClass extends Sample
public void fnsetValue(String sval)
super.setValue(sval);
class check
public static void main(String arg[])
ChildClass chld=new ChildClass();
chld.fnsetValue("pavan");
chld.setValue("pavan");
Note : {color:#ff0000}Kindly don't change the access specifiers.{color}
I need that the "setValue" method should not be accessed by "ChildClass" object.
Thanks u

hi
Thank u for replying and I have solved the issue in the following manner
class Sample
     public void setValue(String sval)
          System.out.println("sValue is : "+sval);
class ChildClass
     InnerClass iclass;
     private Childclass()
          iclass = new InnerClass();
     public static ChildClass getIstance()
          new ChildClass();
     public void fnsetValue(String sval)
          iclass.setValue(sval);
     private class InnerClass extends Sample
          public Innerclass()
               super();
class check
     public static void main(String arg[])
          ChildClass chld=chld.getIstance()
          chld.fnsetValue("pavan");
          chld.setValue("pavan"); //No this not visible mark the statement comment
}

Base class vs derived class

We have entity classes that we use to access our database. We have subclasses derived from these entity classes that apply business rules. For instance, the base class AddressEntity has a
setAddress2(string) that AddressEntity.select() uses to set a class variable with data retrieved from the database. The derived class Address also has a setAddress2(string) method that puts restrictions on the length of the data. I want the AddressEntity.select() method to use the base class method AddressEntity.setAddress2(). I've tried using this.setAddress2() in AddressEntity.select() but the derived class method is still used. Any suggestions?
Thanks,
Joe

If you need to call some methods on the base class sometimes and some methods on the derived class other times, but using the same object, then yes dubwai is right you should revisit your Object hierarchy.
One simple way to do what you are asking is to have your method(s) look like this:
void setAddress2(String sAddress) { setAddress2(sAddress, true); }
void setAddress2(String sAddress, boolean bRestrictLength) {
// real method
}then you could just look at the variable bRestrictLength to see if you need to restrict the length, and have it default to true. In this way you can use overloading to solve your problem.

Invoking Derived Class Method

Hi pls go through the below code, can any one give me solution how to access the Derived class method in this Point.
Note: In the below code , only in runtime we will come to know which Derived class method is going to invoke(So in runtime we will get Derived class name in the form of String). So Iam trying to Use Class.forName("Clas name") to create the instance of the Derived class and then type casting to base class.
Why iam casting to base class is , since only in the run time we are geting the Derived class name.
Result : iam geting the compiletime error says that no valid method fond in Mybase though it contains the reference of derived.
abstract class MyBase
public void display(int i)
System.out.println(" Base class Method");
class MyDerived extends MyBase
public void display(String str)
System.out.println("Derived class Mthode");
class MyMain
public static void main(String arg[])
String DrivObj=arg[0];
MyBase baseObj=(MyBase) Class.forName("DrivObj").newInstance();
baseObj.display("SomeString"); }
}

The problem is, can not have subclass reference bcoz
iam geting the subclass name only in the runtime and
one more thing is cant touch my base and subclass to
do changes as u said Your design is then definately very bad.
, is there any other way to do
it.Yes, you can use reflection to invoke the method.
Kaj

Explizit using methods of base class

when using a base class reference from an abstract class A and creating an object of subclass B
A ref_A = new B();
assuming we have implemented the method m() in A and B, then
ref_a.m()
calls Method m of subclass B
(dynamic binding, fine)
Is there a possibility to force explicitely the call of method m of superclass A.
(i mean not a call from Method m in B with super())

are you absolutely sure ?I am sure. Perhaps you are thinking of C++ (and if you're not, I am!) where you can write: ref_A.A::m(),
but there's no way from the client code to do that in Java. If you really need to do this, your
design of A should reflect it:
public abstract class A {
    public final void mOldSchool() {...}
    public void m() { mOldSchool(); }
public class B extends A {
    public void m() {...}
}I agree with Kayaman, though: question your design. In the abstract, this is a shakey design.

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.

Override a private method in a Base class?

How can a subclass override a final method in its superclass.
This code compiles cleanly.
How is this possible?
Or Am I overlooking any point?
class MySuperClass{
private final String getMessage(){
     return "hello";
protected String getAnotherMessage(){
     return getMessage() + "world";
class MySubClass extends MySuperClass{
private final String getMessage(){
     return "hi";
public String getAnotherMessage(){
   return "anothermessage";
}

getMessage is declared as private in the base class, and therefor cannot be overridden in any subclass.
Edit: I think I understand the question better now. You want to know why it compiles when you think it shouldn't. It's because the private method isn't really inherited at all. Your subclass created a brand new private method of the same signature, but it's completely unrelated.

Adding methods to base classes

How are new methods proposed and adopted for the base classes?

Your question is unclear and I doubt if it has anything to do with JNDI.

How to call a method of a base class if the base class is abstract...

This is my sample code>>>>
abstract class b {
     public void display() {
          System.out.println("I am in Base Class");
class test extends b {
     public static void main(String[] args) {
          test obj = new test();
          obj.display();
     public void display() {
          System.out.println("I am in Derived Class");
I want to call base class version of display with derived class object.........is it possible....

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Enough with the friggin' zombie threads already!

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

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;
   }

Flex/AS3 Best way to construct a derived class instance from an existing base class instance?

What is the best way to handle the instantiation of a derived class from an existing base class.
I have a base class which is being created via remote_object [RemoteClass alias] from the server.   I have other specialized classes that are derived from this baseclass, but serialization with the server always happens with the base class.     The base class has meta data that defines what the derived class is, for example
[RemoteClass (alias="com.myco...')]
public Class Base
     public var derivedType:String;
     public function Base()
public Class Derived extends Base
     public "some other data"
     public function Derived()
In my Cairgorm command which retrieves this object from ther server I want to do this:
public function result (event: Object):void
    var baseInstance:Base = event.result;
     if (baseInstance.derivedType = "derived")
          var derivedInstance:Derived = new Derived( baseInstance );
What is the most efficient way of doing this?   It appears to me that doing a deep-copy/clone and instantiation of the derived class is pretty inefficient as far as memory allocation and data movement via the copy.

Thanks for the assistance. Let me try to clarify.
MY UI requires a number of composite classes.    The individual components of the composite classes are being transfered to/from the server at different times depending upone which component has changed state.    The construction of the composite classes from the base class happens in my clients business logic.
Composition happens in a derived class; but server syncronization happens using the base class.    When I recieve the object from Blazeds through the remote object event, it is in the form of the base class. I then need to instantiate the derived class and copy the elements of the base class into it (for later composite construction).   And likewise when sending the base class back to the server, I need to upcast the derived class to its base class.   But in this case just a mere upcast does not work. I actually need to create a new base class and copy the attrbutes into it. I believe this is limitation of how remoting works on Flex/AS3.
My question is, what is the best way to turn my base class into it's derived class so further composite construction can take place.   The way I am currently doing it is to create a load method on the base class, that takes the base class as on argument. The load function, copies all of the instance attribute references from the base class to the target class.
public Class Base
     public function Base()
     public function load(fromClass:Base)
    { // copy the references for all of the instance attributes from the fromClass to this class }
Then, after I recieve the base class from the server.   I create a new derived class and pass the base class into the load function like this:
            for (var i:int=0; i < event.result.length; i++) {
                var derived:Derived = new Derived();
                derived.load(event.result[i]);
The drawbacks of this approach is that it now requires 2 extra instance creations per object serialization.   One on recieving the object from the server and one sending it to the server.    I assume copying references are pretty efficient. But, there is probably some GC issues.     The worst of it is in code maintenance.   The load function now has to be manually maintained and kept in sync with the server class.
It would be interesting to hear how others have solved this problem.      The server side is an existing application with around 2M LOC, so changing the code on the server is a non-starter.
Thanks for your help.

Synchronization In Base Class Method

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