From abstract class to public class

I am developing a editor base application...wondering that how to cancel the abstract class and put all the abstract class methods into the public class..?? thanks

Is this a C++ question? If so, you should post it in the C++ forum. If it is a Java question, post in the Java forum.
In either case, please make your question more specific. It sounds like all you have to do is copy the functions from the abstract class to the derived class, remove the dependency on the abstract class, and delete the abstract class from the source code. Presumably that is not what you are asking.

Similar Messages

No instances can be created from abstract classes

Dear SAPGurus,
I have developed a oData Service in my backend system & able to register the service in the gateway hub system. When i try to execute the metadata of the service from gateway system i am able to see the metadata with list of entity types availble in the data model.
But when i try to execute with entity set i am getting the following error.
"The class 'ZCL_ZGRC_DATA_MODEL_DPC' is abstract. No instances can be created from abstract classes."
Where my data model provider class name is 'ZCL_ZGRC_DATA_MODEL_DPC'
Kindly help me.
Thanks & Regards,
Rumeshbabu S

Hello Rumesh,
I do not think the error which u are getting is because of System Alias setting in SPRO.
Its something else which is really strange.
However the below is the setting to be maintained in GW SPRO system alias when u have a environment setup like u have now.
I mean the way u have created service and registered -
In ECC system u have created service using builder.
In GW system u have registered it and trying to access now via an RFC destination.
We have the same setup like u have now and we do not have any issues. We have also maintained the System Alias like i have shared in screen shot.
Check your System Alias config once in SPRO. But i dont think this is causing problem in your case. Still check once.
As per my understanding, from GW its trying to hit the DPC class and hence i feel system alias setting is correct in your case.
Problem is something else which is really strange.
Check error logs and see if it can. Share the error log please.
Regards,
Ashwin

How to read data from abstract class

Hi,
I have an abstract class which has a try block in the run method which looks like this:
public void run()
throws exception
try
ArrayList xCoord = new ArrayList();
Double xValue = null;
for (j=0; j<10; j++)
xValue = new Double (table.getX(j).toDouble());
xCoord.add(xValue); // to populate arraylist
i also have the required catch statements, i have not written them here to keep in concise.
My question is: How do I read the values stored in the xCoord arraylist from another 'concrete' class derived from the above abstract class.
I know that for this, I first have to be able to execute the above "run" method, because that is how the arraylist will get populated with values. But how do I do this from the concrete class?
Then, once the arraylist is formed, how do I read the values from the concrete class, without copying all the code?
Any guidance will be really helpful. Thanks -- Vinay.

Add a public or protected accessor (getter) method to retrieve the value calculated in run(). Modify run() to store the results in an instance variable in the abstract class.
- Saish

Geting subclass info from abstract class

Does ne one know how i can retreive informtion from the subclasses of an abstract class by creatinig an instance of the abstract class.
are Methods such as getClass used?

Does ne one know how i can retreive informtion from
the subclasses of an abstract class by creatinig an
instance of the abstract class.You can never create an instance of the abstract class. That is why they are called abstract.
>
are Methods such as getClass used?
Coming to your actual question, a superclass will not know anything about its children. So you will have to do something else get that information.
Maybe inspecting all the classes in a classloader and checking its parent will be an option. I do not think this is possible, because ClassLoader does not provide a mechanism to get all the classes.
Somebody else might give you a better answer. I am just trying to answer one part of your question concerning abstract classes.

Method inheritence from abstract classes, and arguments

I'm trying to do something a little weird. I'm writing a pretty complicated wrapper/adapter for two platforms, and I'd like to have an abstract method passed on to child classes, but with the type of the single argument specified by the child class. Is this possible?
Example
public abstract class AbstractParent {
public abstract void foo([ambiguousType] arg);
public class ChildOne extends AbstractParent {
public void foo(TypeA arg) {
//body
public class ChildTwo extends AbstractParent {
public void foo(TypeB arg) {
//body
}TypeA and TypeB have no common supertype beyond Object, and I'd rather not just do instanceof checks and throw errors. Does anyone know of a solution? Can I elaborate any better?

Perhaps you could use generics?
    public abstract class AbstractParent<E> {
        public abstract void foo(E arg);
    public abstract class ChildOne extends AbstractParent<String> {
        public void foo(String arg) {
    public abstract class ChildTwo extends AbstractParent<Integer> {
        public void foo(Integer arg) {
    }

Why does this abstract class and method work without implement it?

hi,
I have seen many times that in some examples that there are objects made from abstract classes directly. However, in all books, manual and tutorials that I've read explain that we MUST implement those methods in a subclass.
An example of what I'm saying is the example code here . In a few words that example makes Channels (java.nio.channel) and does operations with them. My problem is in the class to make this channels, because they used the ServerSockeChannel class and socket() method directly despite they are abstracts.
   // Create a new channel: if port == 0, FileChannel on /dev/tty, else
   // a SocketChannel from the first accept on the given port number
private static ByteChannel newChannel (int netPort)
      throws Exception
      if (netPort == 0) {
         FileInputStream fis = new FileInputStream ("/dev/tty");
         return (fis.getChannel());
      } else {
//CONFLICT LINES
         ServerSocketChannel ssc = ServerSocketChannel.open(); //<--I have never thought do that!! Anyway, how it is static method may work.
         ssc.socket().bind (new InetSocketAddress (netPort)); //<--but here, this method (socket) is abstract. WHY RETURN A SOCKET???????? this mehod should be empty by default.
         System.out.print ("Waiting for connection on port "
            + netPort + "...");
         System.out.flush();
         ByteChannel channel = ssc.accept();
         ssc.close();
         System.out.println ("Got it");
         return (channel);
   } I test this code and works fine. So why can it be??
Also, I read that the abstract classes can't have static methods. Is it true???
Please Help!!
PS: i have seen this kind of code many times. So i feel that I don't understand how its really the abstract methods are made.
PS2: I understand that obviously you don't do something like this: *"obj = new AbstractClass(); "*. I dont understand how it could be: ServerSocketChannel ssc = ServerSocketChannel.open(); and the compiler didn't warn.

molavec wrote:
ServerSocketChannel ssc = ServerSocketChannel.open(); //<--I have never thought do that!! Anyway, how it is static method may work.
The static method creates an instance of a class which extends ServerSocketChannel, but is actually another non-abstract class.I thought that, but reading the documentation I saw that about open() method:
Opens a server-socket channel.
The new channel is created by invoking the openServerSocketChannel method of the system-wide default SelectorProvider object.
The new channel's socket is initially unbound; it must be bound to a specific address via one of its socket's bind methods before connections can be accepted.
...and the problem is the same openServerSocketChannel is abstract, so i don't understand how it could return a ServerSocketChannel.There is a concrete implementation class that has implemented that method.
I guess that really the open() method use a SelectorProvider's subclase but it doesn't appear in the doc.It doesn't need to. First, you don't care about those implementation details, and second, you know that if the class is abstract, it must use some concrete subclass.
Ok, I speak Spanish by default (<-- this sounds like "I am a machine", ^_^' ). So, I didn't know how to say that the method would be {}. Is there a way to say that?? I recommendable for me to know, for the future questions o answers.Not sure what you're saying here. But the other respondent was trying to explain to you the difference between an abstract method and an empty method.
// abstract method
public abstract void foo();
// empty method
public void bar() {
Which class does extend ServerSocketChannel? I can not see it.It may be a package-private class or a private nested class. There's no need to document that specific implementation, since you never need to use it directly.

Question about Classes, Abstract Classes and Interfaces.

I have been experimenting with Classes, Abstract Classes and Interfaces and wonder if anyone can explain this to me.
I was looking for a way to assign a value to a variable and then keep it fixed for the session and have devised this.
First I create an abstract class like this:
public abstract class DatabaseConnection {
private static String ServerName = null;
public static void setServerName(String serverName) {
          ServerName = serverName;
     public static String getServerName() {
          return ServerName;
}and then I created an interface
public interface DatabaseAccess {
     String servername = DatabaseConnection.getServerName();
}And finally the class itself with some test lines in it so I could see what was going on:
public class CreateDatabase extends DatabaseConnection implements DatabaseAccess {
     public static void main (String args[]){
          new CreateDatabase();
     public CreateDatabase(){
          setServerName("Server Name 1");
          System.out.println ("Before update ");
          System.out.println ("ServerName from Interface           = " + servername);
          System.out.println ("ServerName from Abstract Class = " + getServerName());
          System.out.println ("After update ");
          setServerName("Server Name 2");
          System.out.println ("ServerName from Interface           = " + servername);
          System.out.println ("ServerName from Abstract Class = " + getServerName());
          System.out.println ("==========================");
}The output I get from the above is:
Before update
ServerName from Interface           = Server Name 1
ServerName from Abstract Class = Server Name 1
After update
ServerName from Interface           = Server Name 1
ServerName from Abstract Class = Server Name 2
==========================I also tried this in another class which calls the above class to see if I get the same effect
public class CheckDatabaseAccess {
     public static void main (String args[]){
          new CreateDatabase();
          CreateDatabase.setServerName("Server 3");
          System.out.println("CreateDatabase "+CreateDatabase.servername);
          CreateDatabase.setServerName("Server 4");
          System.out.println("CreateDatabase "+CreateDatabase.servername);
          CreateDatabase.setServerName("Server 5");
          System.out.println("CreateDatabase "+CreateDatabase.servername);
}The output of which is this:
Before update
ServerName from Interface           = Server Name 1
ServerName from Abstract Class = Server Name 1
After update
ServerName from Interface           = Server Name 1
ServerName from Abstract Class = Server Name 2
==========================
CreateDatabase Server Name 1
CreateDatabase Server Name 1
CreateDatabase Server Name 1Can anyone explain why I appear to only be able to change or set the ServerName only the once?
Is this the correct way to do it? If it is it's exactly what I am looking for, a way to set the value of variable once in a session and then prevent it being changed.
Or is there a better way of doing this.
What I want to use this for is for example, storing the accesses to a database on a server. I won't know what server the database will be stored on nor what the database is called so I create an INI file which stores this information in encrypted format, which is set by the database administrator. It occurs to me I can use this method to then retrieve that data once and once only from the INI file and use that throughout the life of the session to access the database.
Any help appreciated
Regards
John

Not gonna read all of it, but this jumps out:
public abstract class DatabaseConnection {
private static String ServerName = null;
public interface DatabaseAccess {
     String servername = DatabaseConnection.getServerName();
}You have two completely separate variables (with two different names, for that matter, since you were inconsistent in your capitalization, but it wouldn't make a difference if they did have the same name with the same case). And the one in the interface is implicitly public, static, and final.
Anytime you refer to "servername" through a reference of type DatabaseAccess, it refers to the one declared in the interface.
Anytime you refer to "ServerName" inside the DatabaseConnection class, it refers to the one declared in that class.

Abstract Class and polymorphism - class diagram

Hi,
]Im trying to draw a class diagram for my overall system but im not too sure how to deal with classes derived from abstract classes. I'll explain my problem using the classic shape inheritance senario...
myClass has a member of type Shape, but when the program is running shape gets instantiated to a circle, square or triangle for example -
Shape s = new circle();
since they are shapes. But at no stage is the class Shape instantiated.
I then call things like s.Area();
On my class diagram should there be any lines going from myClass directly to circle or triangle, or should a line just be joining myClass to Shape class?
BTW - is s.Area() polymorphism?
Thanks,
Conor.

Sorry, my drawing did not display very well.
If you have MyClass, and it has a class variable of type Shape, and the class is responsible for creating MyClass, use Composition on your UML diagram to link Shape and MyClass.
If you have MyClass, and it has a class variable of type Shape, and the class is created elsewhere, use Aggregation on your UML diagram to link Shape and MyClass.
If you have MyClass, and it is used in method signatures, but it is not a class variable, use Depedency on your UML diagram to link Shape and MyClass. The arrow will point to Shape.
Shape and instances of Circle, Triangle, Square, etc. will be linked using a Generalization on your UML diagram. The arrow will always point to Shape.
Anything that is abstract (class, method, variable, etc.) should be italicized. Concrete items (same list) should be formatted normally.
BTW, the distinction between Composition, Aggregation and Dependency will vary from project to project or class to class. It's a gray area. Just be consistent or follow whatever guidelines have been established.
- Saish

About Abstract class

Hi All,
I m inherting from abstract class . So is it mandatory for me to provide implemenation for all methods that r defined in abstract class
i m getting error like this:
subclass class is not abstract ,does not override abstract method "methodname" in superclass
Thanks in advance
Waiting for replies
Amar

- you need to override all methods from your abstract
superclass.....You don't have to override anything unless you want to, but you have to supply implementation for all abstract classes. If you don't you will have to declare the subclass abstract and let another subclass down the hierarchy finish the job. Eventually all abstract classes must be implemented otherwise objects cannot be instantiated. For that a class must be fully concrete.

Calling a method from an abstract class in a seperate class

I am trying to call the getID() method from the Chat class in the getIDs() method in the Outputter class. I would usually instantiate with a normal class but I know you cant instantiate the method when using abstract classes. I've been going over and over my theory and have just become more confused??
Package Chatroom
public abstract class Chat
   private String id;
   public String getID()
      return id;
   protected void setId(String s)
      id = s;
   public abstract void sendMessageToUser(String msg);
Package Chatroom
public class Outputter
public String[] getIDs()
     // This is where I get confused. I know you can't instantiate the object like:
        Chat users=new Chat();
        users.getID();
I have the two classes in the package and you need to that to be able to use a class' methods in another class.
Please help me :(

I have just looked over my program and realised my class names are not the most discriptive, so I have renamed them to give you a clearer picture.
package Chatroom
public abstract class Chatter
private String id;
public String getID()
return id;
protected void setId(String s)
id = s;
I am trying to slowly build a chatroom on my own. The Chatter class is a class that will be used to represent a single logged in user and the user is given an ID when he logs in through the setId and getID() methods.
package Chatroom;
import java.util.Vector;
public class Broadcaster
private Vector<Chatter> chatters = new Vector<Chatter>();
public String[] getIDs()
// code here
The Broadcaster class will keep a list of all logged-in users keeps a list of all the chats representing logged-in users, which it stores in a Vector.I am trying to use the getIDs() method to return an array of Strings comprising the IDs of all logged-in users, which is why im trying to use the getID() method from the Chat class.
I apologise if I come across as clueless, it's just I have been going through books for about 4 hours now and I have just totally lossed all my bearings

Casting to an abstract class from a different classloader

I have a class Special that extends an abstract class Base. In my code I use a URLClassLoader to load the class Special and I then want to cast Special to Base. If I do this I get a ClassCastException because the classes are loaded from different classloaders. I can't have the URLClassLoader and the class that performs the cast extend a parent ClassLoader that knows about the Base class. What I want to be able to do is something like this:
URLClassLoader loader = new URLClassLoader(codebase, null);
Class baseClass = loader.loadClass(className);
Base baseObj = (Base)baseClass.newInstance();
I have seen some post that suggest I can achieve this using Reflection but I am not sure how to go about this. Any help would be appreciated.
Thanks
Jim.

Thanks for your help so far but I still can't do the casting, consider this example:
//Base.java
package classTest;
public interface Base
     public abstract void execute();
//ConcBase.java
package classTest;
public class ConcBase implements Base
     public void execute()
          System.out.println("execute in ConcBase called");
I compile these files and jar them into work.jar
I now have my application:
//Test.java
import java.net.*;
import java.io.*;
import classTest.*;
public class Test
public static void main(String[] args)
          Test t = new Test();
          t.test();
     public void test()
          try
               File file = new File("D:/Projects/classloadTest/work.jar");
               URL[] codebase = {file.toURL()};
               ClassLoader ccl = getClass().getClassLoader();
               ccl.loadClass("classTest.Base");
               URLClassLoader ucl = new URLClassLoader(codebase,ccl);
               Class conClass = ucl.loadClass("classTest.ConcBase");
               classTest.Base b = (classTest.Base)conClass.newInstance();
               b.execute();
          catch(Exception t)
               System.out.println("thowable caught");
               t.printStackTrace(System.out);
I compile this and run it with this command:
java -classpath D:\Projects\classloadTest\work.jar;. Test
This runs as I would expect, however I have set the parent class loader of my custom URLClassLoader to the one that does the cast, this means that Base and ConcBase are both being picked up by the application class loader as my custom class loader delegates to its parent. This is the current behaviour I have in my proper application and it is causing problems, I don't want the class that implements Base to delegate to any class on the main applications classpath. If I change the line:
URLClassLoader ucl = new URLClassLoader(codebase,ccl);
In Test.java to:
URLClassLoader ucl = new URLClassLoader(codebase,null);
I get a ClassCastException, this is because the class that does the cast (Test) loads Base from it's classpath and ConcBase is loaded from the URLClassLoader. After spending more time looking at this problem I don't think there is anyway to resolve but if anyone thinks there is please tell me.
Many thanks
Jim.

Is it possible to call methods from another class from within an abstract c

Is it possible to call methods from another class from within an abstract class ?

I found an example in teh JDK 131 JFC that may help you. I t is using swing interface and JTable
If you can not use Swing, then you may want to do digging or try out with the idea presented here in example 3
Notice that one should refine the abstract table model and you may want to create a method for something like
public Object getValuesAtRow(int row) { return data[row;}
to give the desired row and leave the method for
getValuesAt alone for getting valued of particaular row and column.
So Once you got the seelcted row index, idxSelctd, from your table
you can get the row or set the row in your table model
public TableExample3() {
JFrame frame = new JFrame("Table");
frame.addWindowListener(new WindowAdapter() {
public void windowClosing(WindowEvent e) {System.exit(0);}});
// Take the dummy data from SwingSet.
final String[] names = {"First Name", "Last Name", "Favorite Color",
"Favorite Number", "Vegetarian"};
final Object[][] data = {
     {"Mark", "Andrews", "Red", new Integer(2), new Boolean(true)},
     {"Tom", "Ball", "Blue", new Integer(99), new Boolean(false)},
     {"Alan", "Chung", "Green", new Integer(838), new Boolean(false)},
     {"Jeff", "Dinkins", "Turquois", new Integer(8), new Boolean(true)},
     {"Amy", "Fowler", "Yellow", new Integer(3), new Boolean(false)},
     {"Brian", "Gerhold", "Green", new Integer(0), new Boolean(false)},
     {"James", "Gosling", "Pink", new Integer(21), new Boolean(false)},
     {"David", "Karlton", "Red", new Integer(1), new Boolean(false)},
     {"Dave", "Kloba", "Yellow", new Integer(14), new Boolean(false)},
     {"Peter", "Korn", "Purple", new Integer(12), new Boolean(false)},
     {"Phil", "Milne", "Purple", new Integer(3), new Boolean(false)},
     {"Dave", "Moore", "Green", new Integer(88), new Boolean(false)},
     {"Hans", "Muller", "Maroon", new Integer(5), new Boolean(false)},
     {"Rick", "Levenson", "Blue", new Integer(2), new Boolean(false)},
     {"Tim", "Prinzing", "Blue", new Integer(22), new Boolean(false)},
     {"Chester", "Rose", "Black", new Integer(0), new Boolean(false)},
     {"Ray", "Ryan", "Gray", new Integer(77), new Boolean(false)},
     {"Georges", "Saab", "Red", new Integer(4), new Boolean(false)},
     {"Willie", "Walker", "Phthalo Blue", new Integer(4), new Boolean(false)},
     {"Kathy", "Walrath", "Blue", new Integer(8), new Boolean(false)},
     {"Arnaud", "Weber", "Green", new Integer(44), new Boolean(false)}
// Create a model of the data.
TableModel dataModel = new AbstractTableModel() {
// These methods always need to be implemented.
public int getColumnCount() { return names.length; }
public int getRowCount() { return data.length;}
public Object getValueAt(int row, int col) {return data[row][col];}
// The default implementations of these methods in
// AbstractTableModel would work, but we can refine them.
public String getColumnName(int column) {return names[column];}
public Class getColumnClass(int col) {return getValueAt(0,col).getClass();}
public boolean isCellEditable(int row, int col) {return (col==4);}
public void setValueAt(Object aValue, int row, int column) {
data[row][column] = aValue;
};

WebService from an Abstract Class

Winthin JDev 10.1.2 is there a way to automatically create a J2EE WebService from an abstract class as you would with an public class? If so, how? Thank you in advance.

Justin,
may I ask what you hope to achieve by exposing an abstract class as a Webservice?
Frank

Classes which inherited from the same abstract class calling each other

I have a design that contains such classes.
1) Media - defines some methods to get data which business logic wants and some others to deal with data
media.java
public abstract class Media {
   public abstract Object getSomeData(String type);
   public void methodForMedia() {
       // do something here...
}And certainly, a lot of classes derive from it to function differently.
etc,
DynamicMedia.java
public class DynamicMedia extends Media {
   public Object getSomeData(String type) {
      // get some data here...
      return somedata;
   public void methodForMedia() {
       // inherits and overrides here
   public void methodForDynamicMedia(String data1, Object data2) {
       // do something here...
}FixedMedia.java
public class FixedMedia extends Media {
   public Object getSomeData(String type) {
      // get some data here...
      return somedata;
   public void methodForMedia() {
       // inherits and overrides here
   public Object getFixedMediaData(String type) {
       // get some fixed data here
       return someFixedData;
}2) Business - which implements business logic
public class Business {
     public void transactionOne() {
           FixedMedia fm = getMedia(FixedMedia.class);
           Object fixedData = fm.getFixedMediaData("fixedDataType");
           DynamicMedia dm = getMedia(DynamicMedia.class);
           dm.methodForDynamicMedia("somedata", fixedData);
}Calling methods defined in DynamicMedia might need
many data that can only be retrieved through FixedMedia
(or any similar class just as FixedMedia - derived from Media and handle "fixed" data).
So we decide to define a field to contain a reference of FixedMedia or its container (a list, map)
in DynamicMedia to reduce the codes.
But it results the coupling between DynamicMedia and FixedMedia(s).
Which design is better on testing, quality?

Why not just use an interface?
And why does methodForDynamicMedia() exist only there?
So we decide to define a field to contain a reference of FixedMedia or its container (a list, map)
in DynamicMedia to reduce the codes.Sounds like a muddled design. Sometimes you might make an implementation decision that adversely impacts the design but you better have a better reason than just because it reduces some code. Maybe it reduces a lot of code, but if so then that might suggest something is wrong with the design.

Inheriting from an abstract class

Hi all,
I'm using a certain graphics package and I need to modify a functionality of one of its classes called, say, PlainAxis. For this purpose I define a class MyAxis that derives from the class Axis which is the base class for PlainAxis as well. The Axis class is abstract; it has two abstract methods - draw() and copy(). I provide these two methods in MyAxis, so, it can be instantiated. Still I get the following error message during the compilation:
MyAxis should be declared abstract; it does not define draw() in Axis
Here is the command I'm executing (sgt.jar contains classes of the graphics package I'm using):
javac -g -classpath .:./sgt.jar *.java -d .
What am I doing wrong? Why does this error occure for the draw() method only?
Thank you for the help!

You probably didn't define draw() with the exactsame
method signatureBelieve me I did :) This was the first thing I
checked when I saw this error for the first time...
Any other suggestions? :)The possibilities that I can think of are (most of these have already been suggested):
1. you didn't define draw with the correct signature
2. you're not extending the class you think you're extending
3. you're not compiling the class you think you're compiling
4. there's a bug in your compiler
I'd say 3 is extremely unlikely. So without seeing your code, we can only guess, but I would guess #1.

From abstract class to public class

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