Can an abstract class extend another abstract class?

Is it possible for an abstract class to extend another abstract class?
Say
public abstract class AComponent extends JComponent {
Thanks.

Yes

Similar Messages

Inner Class extending the outer class

Could anyone explain this code to me? It can compile and run. Could anyone tell me what the class Main.Inner.Inner is? What members does it consists of? How the compiler manage to build such a class?
public class Main {
    public static class Inner extends Main {
    public static void main(String[] args) {
        System.out.println("Hello, world.");
}

By the way, it's not really an inner class, because it's static. It's just a nested class.
You might want to have a nested class extend its enclosing class if, maybe, you wanted to delegate to subclasses and didn't want to create a lot of extra source code files, which might make sense if the nested subclasses were really small.
public abstract class Animal {
public abstract void makeSound();
private Animal() {} // can't be directly instantiated
private static class Dog extends Animal {
    public void makeSound() { System.out.println("woof"); }
private static class Cat extends Animal {
    public void makeSound() { System.out.println("meow"); }
private static class Zebra extends Animal {
    public void makeSound() { System.out.println("i am a zebra"); }
public static Animal get(String desc) {
    if ("fetches sticks".equals(desc)) {
      return new Dog();
    if ("hunts mice".equals(desc)) {
      return new Cat();
    if ("stripey horse".equals(desc)) {
      return new Zebra();
    return null;
public class AnimalTest {
public static void main(String... argv) {
    Animal a = Animal.get("fetches sticks");
    a.makeSound();
}

How to call a Java class from another java class ??

Hi ..... can somebody plz tell me
How to call a Java Class from another Java Class assuming both in the same Package??
I want to call the entire Java Class (not any specific method only........I want all the functionalities of that class)
Please provide me some slotuions!!
Waiting for some fast replies!!
Regards
Smita Mohanty

Hi Smita,
you just need to create an object of that class,thats it. Then you will be able to execute each and every method.
e.g.
you have developed A.java and B.java, both are in same package.
in implementaion of B.java
class B
            A obj = new A();
             //to access A's methods
             A.method();
            // to access A's variable
            //either
           A.variable= value.
           //or
           A.setvariable() or A.getvariable()

Can a Class extend a Main Class

Can a Class extend a Class containing
"public static void main(String[] args)"

What sort of methods a class has doesn't determine
whether it may be extended or not. If the class is
marked Final determines whether it may be subclassed
or not.
And if it is accesible in the context that it is being used in.

How to refresh a JTable of a class from another thread class?

there is an application, in server side ,there are four classes, one is a class called face class that create an JInternalFrame and on it screen a JTable, another is a class the a thread ,which accept socket from client, when it accept the client socket, it deal the data and insert into db,then notify the face class to refresh the JTable,but in the thread class I used JTable's revalidate() and updateUI() method, the JTable does not refresh ,how should i do, pls give me help ,thank you very much
1,first file is a class that create a JInternalFrame,and on it there is a table
public class OutFace{
public JInternalFrame createOutFace(){
JInternalFrame jf = new JInternalFram();
TableModel tm = new MyTableModel();
JTable jt = new JTable(tm);
JScrollPane jsp = new JScrollPane();
jsp.add(jt);
jf.getContentPane().add(jsp);
return jf;
2,the second file is the main face ,there is a button,when press the button,screen the JInternalFrame. there is also a thread is beggining started .
public class MainFace extends JFrame implements ActionListener,Runnable{
JButton jb = new JButton("create JInternalFrame");
jb.addActionListener(this);
JFrame fram = new JFrame();
public void performance(ActionEvent e){
JInternalFrame jif = new OutFace().createOutFace(); frame.getContentPane().add(JInternalFrame,BorderLayout.CENTER);
public static void main(String[] args){
frame.getContentPane().add(jb,BorderLayout.NORTH);
frame.pack();
frame.setVisible(true);
ServerSokct ss = new ServerSocket(10000);
Socket skt = ss.accept()'
new ServerThread(skt).start();
3.the third file is a thread class, there is a serversoket ,and accept the client side data,and want to refresh the JTable of the JInternalFrame
public class ServerThread extends Thread{
private skt;
public ServerThread(Sokcet skt){
this.skt = skt;
public void run(){
OutputObjectStream oos = null;
InputObjectStream ios = null;
try{
Boolean flag = flag;
//here i want to refresh the JTable,how to write??
catch(){}
4.second is the TableModel
public class MyTableModel{
public TableModel createTableModel(){
String[][] data = getData();
TableModel tm = AbstractTableModel(
return tm;
public String[][] getData(){
}

Use the "code" formatting tags when posting code.
Read this article on [url http://www.physci.org/codes/sscce.jsp]Creating a Simple Demo Program before posting any more code.
Here is an example that updates a table from another thread:
http://forum.java.sun.com/thread.jspa?forumID=57&threadID=435487

Help! how to refresh the JTable of a class from another thread class

there is an application, in server side ,there are two classes, one is a class called face class that screen a JTable, another is a class the a thread ,which accept socket from client, when it accept the client socket, it deal the data and insert into db,then notify the face class to refresh the JTable,but in the thread class I used JTable's revalidate() and updateUI() method, the JTable does not refresh ,how should i do, pls give me help ,thank you very much

thank you very much !
i tried it ,but the TableModel i used like this ,and how to change the TableModel?
here the files of mine ,pls give me some help,thank you very much
1,first file is a class that create a JInternalFrame,and on it there is a table
public class OutFace{
public JInternalFrame createOutFace(){
JInternalFrame jf = new JInternalFram();
TableModel tm = new MyTableModel();
JTable jt = new JTable(tm);
JScrollPane jsp = new JScrollPane();
jsp.add(jt);
jf.getContentPane().add(jsp);
return jf;
2,the second file is the main face ,there is a button,when press the button,screen the JInternalFrame. there is also a thread is beggining started .
public class MainFace extends JFrame implements ActionListener,Runnable{
JButton jb = new JButton("create JInternalFrame");
jb.addActionListener(this);
JFrame fram = new JFrame();
public void performance(ActionEvent e){
JInternalFrame jif = new OutFace().createOutFace(); frame.getContentPane().add(JInternalFrame,BorderLayout.CENTER);
public static void main(String[] args){
frame.getContentPane().add(jb,BorderLayout.NORTH);
frame.pack();
frame.setVisible(true);
ServerSokct ss = new ServerSocket(10000);
Socket skt = ss.accept()'
new ServerThread(skt).start();
3.the third file is a thread class, there is a serversoket ,and accept the client side data,and want to refresh the JTable of the JInternalFrame
public class ServerThread extends Thread{
private skt;
public ServerThread(Sokcet skt){
this.skt = skt;
public void run(){
OutputObjectStream oos = null;
InputObjectStream ios = null;
try{
Boolean flag = flag;
//here i want to refresh the JTable,how to write?? }
catch(){}
4.second is the TableModel
public class MyTableModel{
public TableModel createTableModel(){
String[][] data = getData();
TableModel tm = AbstractTableModel(
return tm;
public String[][] getData(){
}

Referencing WMI Manageable class from another WMI Class

Hi,
I am trying to have WMI manageable class referring to another WMI manageable class
Something like
[ManagementEntity]
Class A
[ManagementEntity]
Class B
        [ManagementReference(Type = "A")]
        [ManagementProbe]
        public A AClass;
When trying to install the class, I am getting “Type unsupported”
I tried the Microsoft
ManagementReference sample,
http://msdn.microsoft.com/en-us/library/system.management.instrumentation.managementreferenceattribute.aspx
(working fine but the LetterPhonetic class won’t show on the WMI Object Browser)
Ideas will be highly appreciated
My Sample code
using System;
using System.Management.Instrumentation;
using System.Collections.Concurrent;
using System.Collections;
[assembly: WmiConfiguration("root\\ConsoleC", HostingModel = ManagementHostingModel.Decoupled)]
namespace ConsoleDecoupled
    [System.ComponentModel.RunInstaller(true)]
    public class TheInstaller : DefaultManagementInstaller
    public class Program
        public static void Main(string[] args)
            for (int i = 0; i < 10; ++i)
                TestEnumWmi ms = TestEnumWmi.CreateTestEnumWmi();
                ms.teststring = i.ToString();
            InstrumentationManager.RegisterType(typeof(TestEnumWmi));
            InstrumentationManager.RegisterType(typeof(RuntimeConfigSettings));
            Console.WriteLine("Press enter to exit");
            Console.ReadLine();
            InstrumentationManager.UnregisterType(typeof(TestEnumWmi));
            InstrumentationManager.UnregisterType(typeof(RuntimeConfigSettings));
    [ManagementEntity(Singleton = true, Name = "ConfigurationSample")]
    [ManagementQualifier("Description", Value = "Configuration Sample Application")]
    public class RuntimeConfigSettings
        [ManagementProbe]
        public string[] ReadMe;
        private int myVar;
        [ManagementConfiguration]
        public int MyProperty
            get { return myVar; }
            set { myVar = value; Console.WriteLine(value); }
        [ManagementReference(Type = "TestEnumWmi")]
        [ManagementProbe]
        public TestEnumWmi MSS;
        [ManagementBind]
        public RuntimeConfigSettings()
            ReadMe = new string[10];
            for (int i = 0; i < 10; ++i)
                ReadMe[i] = "blah " + i;
    [ManagementEntity(Name = "TestEnumWmi")]
    public class TestEnumWmi
        private TestEnumWmi()
        static internal TestEnumWmi CreateTestEnumWmi()
            TestEnumWmi ms = new TestEnumWmi();
            ms._id = Guid.NewGuid().ToString();
            ms.teststring = "blah";
            ms.TestInt = new Random().NextDouble();
            instantlist.TryAdd(ms._id, ms);
            return ms;
        [ManagementConfiguration()]
        public double TestInt { get; set; }
        [ManagementConfiguration()]
        public string teststring { get; set; }
        [ManagementKey(Name = "ID")]
        public string _id;
        [ManagementBind]
        static public TestEnumWmi GetInstant([ManagementName("ID")] string ID)
            TestEnumWmi ms = null;
            if (instantlist.TryGetValue(ID, out ms))
                return ms;
            else
                throw new InstanceNotFoundException();
        [ManagementEnumerator]
        static public IEnumerable EnumerateTestEnumWmis()
            foreach (var i in instantlist)
                yield return i.Value;
        static internal ConcurrentDictionary<string, TestEnumWmi> instantlist = new ConcurrentDictionary<string, TestEnumWmi>();

Hi,
The Microsoft ManagementReference sample you mentioned contains a bug:
Instead of:
inst.LetterNumber = "Letter = " + i;
inst.PhoneticNumber = "Phonetic = " + i;
The exact text (where spaces in the string are important and must be removed) should be:
inst.LetterNumber = "NumberLetter.Number=" + i;
inst.PhoneticNumber = "NumberPhonetic.Number=" + i;
With this fix, the hierarchy can now be navigated properly.
c.f. my response to the following blog post:
http://juggledthoughts.blogspot.co.uk/2008/06/wmi-association-classes.html
I have also
logged a bug on MSDN Feedback so please vote on this if you'd like them to fix the sample.

How sholud we call one jframe class from another jframe class

Hi
In my application i am calling one jframe class from another jframe clas.
how sholud we make previous jframe inactve when another jframe is invoked?(user sholud not able to make any changes on on parent jframe window when another jframe is invoked)
Pls reply.

Sorry for me it is not possible to change existing code,
pls suggest me any other solution so that i can inactive parent jframe when child jframe execution is going on.

Accesing components of global class in another global class.

Hi,
I am not able to access Public TYPES defined on a class in other class.
Class cl_business_object : has public type tt_records type table of <ztable> with default key.
and when i use it in method of cl_gui , get_records returning rt_records type cl_business_object=>tt_records after making the statement of Class definition cl_business_object load / entering the name of the class in properties tab's .. why does it happen ?
Regards.

Hi, Its ECC 6.0,
We did nto have this problem before, Its kind of new, have no idea why it behaves so ..
And the syntax error is not generated when we are cheking onthe class where it has been used (acessing other class types) , this is activated.
but another 3rd class where this activated class is used, throw up syntactical error showing error in class 2.
" saying components of global class are not accesible, class definition missing"..
but there are statements of class definition load already!!
Regards
Edited by: Trivvka on Aug 11, 2009 5:06 PM

Error 1119 when class extends another class that extends movieclip

hiya
i came across this problem and i have no clue why it's happening. basically, consider 2 nested movieclips on the stage, something like stage -> main -> filler. both movieclips have instance names (main and filler).
in the library, i set main to export for actionscript, using class A:
package {
    import flash.display.MovieClip;
    public class A extends MovieClip {
        public function A ():void {
            trace ('construct A');
            trace (this.filler); // should trace [movieclip] etc
it works fine. now i change it's export settings to use class B, that extends A, and it breaks:
package {
    import flash.display.MovieClip;
    public class B extends A {
        public function B ():void {
            trace ('construct B');
this throws an error 1119: Access of possibly undefined property filler through a reference with static type A.
can anyone give me a hint on that, as it works with class A, but not B extending A? i understand it was meant to work?
many thanks

afaik, if you dont declare super(), flash will make a call for you (but best practice is to call it always).
but i found the "solution" in another forum.
it seems that flash implicitly generates variables if you have instance names/symbols on the stage. there is an option to disable that under publish settings -> Actionscript version -> Settings -> automatically declare stage instances. by disabling that, we were able to declare public var filler:MovieClip; on class A, and that worked.
although, that solution doesnt look attractive to me. the other solution posted on another forum was to make calls to this ["filler"] instead of this.filler. that seems to work fine. i guess it has to do with the automatic variable generated thing.. who knows?
i hope that helps someone else too

How can we call one java class in another java class?

Hi all,
My problem is ,
one java code creates a file i have to send that file through email as an attachment here i wrote a java code to send a mail with attachment
can any one help me how i can implement this. my idea is to write a send mail function in 1st java code which creates the file
Is this a better idea ???plz suggest me.

Hi all,
My problem is ,
one java code creates a file i have to send that file
through email as an attachment here i wrote a java
code to send a mail with attachment
can any one help me how i can implement this. my idea
is to write a send mail function in 1st java code
which creates the file
Is this a better idea ???plz suggest me.may samaaj nahi atay

Thread Pool Executor ( Runnable Class Executing another Runnable Class )

Hi Folks,
I have my main class called ThreadPoolExecutorUser. I have two Runnable classes called XYZ and ABC
in ThreadPoolExecutorUser class I execute the Runnable class XYZ. Which inturn executes Runnable class ABC.
The problem is that the Runnable class ABC is never executed ?. Can some one please explain what I am I doing wrong.
_RB
More Description Below :
*public class ThreadPoolExecutorUser {*
ThreadPoolExecutor dude = new ThreadPoolExecutor (.... );
// I Execute the firest Runnable Xyz here
dude.execute ( XYZ );
Now I have two Runnable inner Classes
*Class XYZ extends Runnable {*
public void run () {
s.o.p ( " I am in Xyz Runnable " );
dude.execute ( ABC );
*class ABC extends Runnable {*
public void run () {
s.o.p ( " I am in ABC Runnable " );
}

Hey folks.... Sorry its a typo in my e-mail. Sorry about that. I am pasting the actual code here.
The problem again is that in the index function only FirstRunnable executes but not the SecondRunnable
final public class Crawler {
    / create an instance of the ISSThreadPoolExecutor /
    private static ThreadPoolExecutor mythreadpoolexecutor = ThreadPoolExecutor.getInstance();
    / Constructor /
    / Index function /
    public void index( .... ) {
        :::::: code :::::::::
        // Execute this folder in a seperate thread.
        this.issthreadpoolexecutor.execute(new FirstRunnable(alpha, beta, gamma));
    / The Inner Class /
    class FirstRunnable implements Runnable {
        public FirstRunnable(int alpha, int beta, int gamma) {
        public void run() {
                        doSomething();
                        // Some other tasks and ...spawn of another thread.
                        issthreadpoolexecutor.execute(new SecondRunnable(a));
         // The Inner Class that Indexes the Folder
          class SecondRunnable implements Runnable {
                  private int ei;
                  public SecondRunnable ( int abc ) {
                        this.ei = abc;
                  public void run() {
                        doSomething ( ".....") ;
          } // End of SecondRunnable Class.
     } // End of FirstRunnable class.
} // End of Crawler Class.

How I call a JApplet class from another JApplet class ?

I have a Japplet class named ConnectionClient and I want to open another JApplet window when I clicked a button.
I tried that call init() method but it is not accomplished. Please help me !

for example:
import java.awt.BorderLayout;
import java.awt.Font;
import java.awt.GridLayout;
import java.awt.Window;
import java.awt.Dialog.ModalityType;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JApplet;
import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;
public class MyApplet extends JApplet
public void init()
    try
      javax.swing.SwingUtilities.invokeAndWait(new Runnable()
        public void run()
          createGUI();
    catch (Exception e)
      System.err.println("createGUI didn't successfully complete");
private void createGUI()
    getContentPane().add(new AppletPanel().getComponent());
class AppletPanel
private JPanel mainPanel = new JPanel();
public AppletPanel()
    JButton showDialog = new JButton("Show Dialog");
    mainPanel.add(showDialog);
    showDialog.addActionListener(new ActionListener()
      public void actionPerformed(ActionEvent e)
        JButton btn = (JButton)e.getSource();
        Window win = SwingUtilities.getWindowAncestor(btn);
        JDialog dialog = new JDialog(win, "My Dialog", ModalityType.APPLICATION_MODAL);
        dialog.getContentPane().add(new DialogPanel().getComponent());
        dialog.pack();
        dialog.setLocationRelativeTo(null);
        dialog.setVisible(true);
public JComponent getComponent()
    return mainPanel;
class DialogPanel
private static final int SIDE = 9;
private JPanel mainPanel = new JPanel();
public DialogPanel()
    JPanel btnPanel = new JPanel(new GridLayout(SIDE, SIDE, 5, 5));
    for (int i = 0; i < SIDE; i++)
      for (int j = 0; j < SIDE; j++)
        JButton btn = new JButton("[" + i + ", " + j + "]");
        btnPanel.add(btn);
    JLabel titleLabel = new JLabel("JDialogs Can Be Complex", SwingConstants.CENTER);
    titleLabel.setFont(titleLabel.getFont().deriveFont(Font.BOLD, 32));
    mainPanel.setLayout(new BorderLayout());
    mainPanel.add(titleLabel, BorderLayout.NORTH);
    mainPanel.add(btnPanel, BorderLayout.CENTER);
public JComponent getComponent()
    return mainPanel;
}

Visual Editor cannot show the class extending a visual class of JFrame

Hi,
We want to create a base frame (BaseFrame) so that every form in our application extending it to share some common properties.
But i found that the class (OrderFrame extends BaseFrame) cannot be shown properly in Visual Editor (run is ok).
Is there any way to resolve it?
Code Ref:
BaseFrame.java
public class BaseFrame extends JFrame {
public BaseFrame() {
try {
jbInit();
} catch (Exception e) {
e.printStackTrace();
private void jbInit() throws Exception {
this.getContentPane().setLayout( null );
this.setSize( new Dimension(400, 300) );
this.setTitle( "Standard JFrame" );
OrderFrame.java
public class OrderFrame extends BaseFrame {
public OrderFrame() {
try {
jbInit();
} catch (Exception e) {
e.printStackTrace();
private void jbInit() throws Exception {
}

Olaf,
When using your own beans it is best to create the bean in one project, and then use it in a second project. So in your example; use Project1.jpr to create, compile, test, debug BaseFrame.java. Then, once you are satisfied with it, use Project2.jpr to create, compile, test, debug MyInternalFrame.java. Your scenario works fine when adopting this approach. However, be sure that MyInternalFrame.java includes the necessary import statement for BaseFrame, and be sure that the classpath for Project2.jpr includes the path to BaseFrame.class. If you are using the default classpath settings for each project (i.e. myclasses) then the classpath concern will be taken care of for you already.
Enjoy.
<BLOCKQUOTE><font size="1" face="Verdana, Arial">quote:</font><HR>Originally posted by olaf:
Hi,
the situation :
BaseFrame extends JInternalFrame
and
MyInternalFrame extends BaseFrame
Now I want to edit MyInternalFrame in the visual editor.
I tried that by making a bean of BaseFrame and addiing the bean to the Palette but MyInternalFrame won't show up in the editor,
anybody knows how to set this up ?
Thanks,
-- olaf<HR></BLOCKQUOTE>
null

How to pass a "object" as a prameter from one java class to another java

hi experts, I want to know "How to pass and get object as a parameter from one java class to another java class". I tried follwoing code just check it and give suggetions..
import Budget.src.qrybean;
public class ConfirmBillPDF extends HttpServlet
qrybean db = new qrybean();
SimplePDFTable pdfTable = new SimplePDFTable();
pdfTable.simplePDFTableShow("2010","2011","1","2","1","131","102");
}Here i want to pass db with simplePDFTableShow method. simplePDFTableShow is in another java class. So how can i do this.
And also i want to know, how this obj will get.
please help me.
Edited by: andy_surya on Jul 14, 2010 7:51 AM

Hi andy_surya
what is this i am not understand
pdfTable.simplePDFTableShow("2010","2011","1","2","1","131","102");but i am try to solve your problem try this
qrybean db = new qrybean();
SimplePDFTable pdfTable = new SimplePDFTable();
pdfTable.simplePDFTableShow(db);and access like this in SimplePDFtable class update your method
simplePDFTable(qrybean tempDB)
// write your code
}

Can an abstract class extend another abstract class?

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