Can a class b subclass of itself wh is diff between instaceof n isInstance

appricate your views

Okay. After reading it three times, I got you. Impoliteness abounds.
No, classes cannot extend themselves.
1) It should be obvious if you put a little thought of your own into it. Why should it be able to?
2) You could have simply wrote some code to try this yourself.
instanceof is an operator. I have no idea what isInstance is supposed to be.
madeaboutjava, you're leeching knowledge, make no useful contributions to this board whatsoever, show no effort or even will to learn anything by yourself rather than being spoonfed by us and basically can be considered a big waste of time. I will no more reply to you.

Similar Messages

Is a class a subclass of itself?

hello experts,
Is a class a subclass of itself?
every class inherits Object class. i heard somewhere that
A class is a subclass of itself. But i dont know how is it?
Can anyone clarify me doubt?
Regards,
SRI.

Java_Aspirant wrote:
hello experts,
Is a class a subclass of itself? no
every class inherits Object class. i heard somewhere that
A class is a subclass of itself. But i dont know how is it?it's wrong. Whoever said that either wasn't talking about Java or didn't know what he was blabbing about (or both).
>
Can anyone clarify me doubt?
aya hef no dbt but dis.

Is a class is subclass of itself?

is a class is subclass of itself?

A class is never a Sub class of itself..
can you do like this...
Class Sample extends Sample
public static void main(String args[])
System.out.println("Hello...");
no way doing like this.....
ok You got it, I think
One thing
Subclass concept is : The private members of the super class cannot be accessed in the subclass and here the super class and sub class are same. then it wont work.......
ok
Edited by: sankar.natukula on Sep 24, 2007 2:04 AM

Is a class subclass of itself

reply for the subject que

Nice find, Jenny. :o)
Despite the fact that the quote comes from Sun, I'm not sure that it's in line with the JLS, to wit:
The subclass relationship is the transitive closure of the direct subclass relationship. A class A is a subclass of class C if either of the following is true:
* A is the direct subclass of C.
* There exists a class B such that A is a subclass of B, and B is a subclass of C, applying this definition recursively.
I haven't found in the JLS where they use the term "strict subclass", or the implied "non-strict" subclass. The JLS only uses the term "subclass" in the context mentioned above. Furthermore JLS is quite clear that a final class cannot have a subclass, which would seemingly preclude a final class from being a subclass of itself.
But, hey, if that's what Sun says the certification is asking for, I'd take their word for it over mine... :o)

Why can't classes with private constructors be subclassed?

Why can't classes with private constructors be subclassed?
I know specifying a private nullary constructor means you dont want the class to be instantiated or the class is a factory or a singleton pattern. I know the workaround is to just wrap all the methods of the intended superclass, but that just seems less wizardly.
Example:
I really, really want to be able to subclass java.util.Arrays, like so:
package com.tassajara.util;
import java.util.LinkedList;
import java.util.List;
public class Arrays extends java.util.Arrays {
    public static List asList(boolean[] array) {
        List result = new LinkedList();
        for (int i = 0; i < array.length; i++)
            result.add(new Boolean(array));
return result;
public static List asList( char[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Character(array[i]));
return result;
public static List asList( byte[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Byte(array[i]));
return result;
public static List asList( short[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Short(array[i]));
return result;
public static List asList( int[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Integer(array[i]));
return result;
public static List asList( long[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Long(array[i]));
return result;
public static List asList( float[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Float(array[i]));
return result;
public static List asList( double[] array) {
List result = new LinkedList();
for (int i = 0; i < array.length; i++)
result.add(new Double(array[i]));
return result;
// Now that we extend java.util.Arrays this method is not needed.
// /**JCF already does this so just wrap their implementation
// public static List asList(Object[] array) {
// return java.util.Arrays.asList(array);
public static List asList(Object object) {
List result;
Class type = object.getClass().getComponentType();
if (type != null && type.isPrimitive()) {
if (type == Boolean.TYPE)
result = asList((boolean[])object);
else if (type == Character.TYPE)
result = asList(( char[])object);
else if (type == Byte.TYPE)
result = asList(( byte[])object);
else if (type == Short.TYPE)
result = asList(( short[])object);
else if (type == Integer.TYPE)
result = asList(( int[])object);
else if (type == Long.TYPE)
result = asList(( long[])object);
else if (type == Float.TYPE)
result = asList(( float[])object);
else if (type == Double.TYPE)
result = asList(( double[])object);
} else {
result = java.util.Arrays.asList((Object[])object);
return result;
I do not intend to instantiate com.tassajara.util.Arrays as all my methods are static just like java.util.Arrays. You can see where I started to wrap asList(Object[] o). I could continue and wrap all of java.util.Arrays methods, but thats annoying and much less elegant.

Why can't classes with private constructors be
subclassed?Because the subclass can't access the superclass constructor.
I really, really want to be able to subclass
java.util.Arrays, like so:Why? It only contains static methods, so why don't you just create a separate class?
I do not intend to instantiate
com.tassajara.util.Arrays as all my methods are static
just like java.util.Arrays. You can see where I
started to wrap asList(Object[] o). I could continue
and wrap all of java.util.Arrays methods, but thats
annoying and much less elegant.There's no need to duplicate all the methods - just call them when you want to use them.
It really does sound like you're barking up the wrong tree here. I can see no good reason to want to subclass java.util.Arrays. Could you could explain why you want to do that? - perhaps you are misunderstanding static methods.
Precisely as you said, if they didn't want me to
subclass it they would have declared it final.Classes with no non-private constructors are implicitly final.
But they didn't. There has to be a way for an API
developer to indicate that a class is merely not to be
instantiated, and not both uninstantiable and
unextendable.There is - declare it abstract. Since that isn't what was done here, I would assume the writers don't want you to be able to subclass java.util.Arrays

How can a class extending MouseAdapter override mouseDragged method?

I've found this code from somewhere, don't remember where
private class DragLimiter extends MouseAdapter {
@Override
public void mousePressed(MouseEvent e) {
pressedX = e.getX();
pressedY = e.getY();
@Override
public void mouseDragged(MouseEvent e) {
label.setLocation(
Math.min(
Math.max(label.getX() + e.getX() - pressedX, BORDER),
panel.getWidth() - label.getWidth() - BORDER),
Math.min(
Math.max(label.getY() + e.getY() - pressedY, BORDER),
panel.getHeight() - label.getHeight() - BORDER));
}The question is how can a class extending MouseAdapter override mousedragged()?
I found that MouseAdapter implements MouseListener whose subinterface is MouseMotionListener, I think this has something to do with the question.
But I've always thought you can only override methods of the super classes or interfaces not vice versa.
I believe I have some kind of fundamental misunderstanding of this and would like to have some help in understanding this.
Thanks

This is more a Java question than a Swing question.
I found that MouseAdapter implements MouseListener whose subinterface is MouseMotionListenerThat's not correct: if you look at MouseAdapter Javadoc, you'll find that it implements both MouseListener and MouseMotionListener (and MouseMotionListener is not a subinterface of MouseListener).
Regardless, if you look at the javadoc, you see that MouseAdapter declares a method public void mouseDragged(MouseEvent). It doesn't matter whether this is also declared by an interface, a subclass can override it all the same.

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 can I make the ipod stop itself after playing one song?

How can I make the ipod stop itself after playing one song?

When playing a song, are the controls at the top of the screen there? (Genius, Shuffle, Loop?)
If not, tap the center of the page once to expose them
now keep tapping the circle on the left part of the exposed controls untill a one (1) appears...

How can a class be notified when an open file is modified externaly ?

Hi!
Can a class that open a File be notified when that file is modified by another program ? If yes how ?
Thanks!

I don't know that any operating system provides facilities to hook into the filestore this way (whatever language you're programming in). Probably the best you can do is to check the last modified time periodically.

Can a class implements more than one interface?

Hello
Can a class implements more than one interface?
Thanks

Of course, this doesn't mean that it won't be a problem though. If the two interfaces have methods with the same signature, but different return types, you won't be able to implement them together. I.E.
interface InterfaceA {
public int doSomething(String myString);
interface InterfaceB {
public String doSomething(String myString);
// Now the classes
// Gives error "Duplicate method doSomething(String) in type ClassA"
public class ClassA implements InterfaceA, InterfaceB {
public int doSomething(String myString) {
    System.out.println("A");
    return 0;
public String doSomething(String myString) {
    System.out.println("B");
    return 0;
// Gives error "The return type is incompatible with InterfaceB.doSomething(String)"
public class ClassB implements InterfaceA, InterfaceB {
public int doSomething(String myString) {
    System.out.println("A");
    return 0;
// Gives error "The return type is incompatible with InterfaceA.doSomething(String)"
public class ClassC implements InterfaceA, InterfaceB {
public String doSomething(String myString) {
    System.out.println("B");
    return 0;
}

When I use my ipad 4 half hours later, it getting hot ? is because the leather cover can't breath or because ipad itself?

when I use my ipad 4 half hours later, it getting hot ? is because the leather cover can't breath or because ipad itself?

The first thing that you should probably do is remove the cover, if it is getting that hot. If it cools down at all, maybe that cover isn't ideal for your iPad.
But your iPad should get really hot and if I am reading your post correctly this occurs after a half hour of use?
From your post its difficult to tell if you have an iPad 4, that gets hot after one half hour of use .... or if you have an iPad, that gets hot after 4-1/2 hours of use.

Diff between CLASSPATH and weblogic.class.path in t3config

Hi,
          My servlets which would run happily in WLS4.0.2 on NT do not run anymore
          in WLS4.5.
          In order to help me troubleshoot this problem will someone please
          explain me the difference between the path mentioned against
          weblogic.class.path in the output of t3config
          and the path mentioned against CLASSPATH in the same output.
          When I type t3config I get the following. What is the diff between the
          lines marked ---->>>>
          WebLogic startup settings are presently:
          CLASSPATH Prefix=
          .;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar
          ------->>>>>CLASSPATH=
          ".;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar;d:\Weblogic\jre1_1\lib\classes.zip;d:\Weblogic\jre1_1\lib\rt.jar;d:\Weblogic\license;d:\Weblogic\classes;d:\Weblogic\lib\weblogicaux.jar;d:\Weblogic\eval\cloudscape\lib\cloudscape.jar"
          JAVA_HOME= "d:\Weblogic\jre1_1"
          WEBLOGIC_HOME="d:\Weblogic"
          system properties:
          weblogic.system.home=d:\Weblogic
          java.compiler=symcjit
          ------->>>
          weblogic.class.path=d:\Weblogic\license;d:\Weblogic\classes;d:\Weblogic\lib\weblogicaux.jar
          INITIAL_HEAP= 32 MB
          MAX_HEAP= 32 MB
          SERVERCLASSPATH=
          ".;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar;d:\Weblogic\jre1_1\lib\classes.zip;d:\Weblogic\jre1_1\lib\rt.jar;d:\Weblogic\classes\boot;d:\Weblogic\eval\cloudscape\lib\cloudscape.jar"


Pankaj,
          It all depends on whether you want to do reload on modify feature or not. If you don't need reload on modify they you can have servlets in weblogic.class.path.
          Two things to remember if you can't invoke servlets.
          1. Do you have the servlet registered.
          2. If not, do you have ServletServlet property uncommented. If this property is not commented out then you have to give the complete path to make servlets work.
          Good luck,
          Prasad
          Pankaj Tandon wrote:
          > Hi,
          > My servlets which would run happily in WLS4.0.2 on NT do not run anymore
          > in WLS4.5.
          > In order to help me troubleshoot this problem will someone please
          > explain me the difference between the path mentioned against
          > weblogic.class.path in the output of t3config
          > and the path mentioned against CLASSPATH in the same output.
          >
          > When I type t3config I get the following. What is the diff between the
          > lines marked ---->>>>
          > WebLogic startup settings are presently:
          >
          > CLASSPATH Prefix=
          > .;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar
          >
          > ------->>>>>CLASSPATH=
          > ".;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar;d:\Weblogic\jre1_1\lib\classes.zip;d:\Weblogic\jre1_1\lib\rt.jar;d:\Weblogic\license;d:\Weblogic\classes;d:\Weblogic\lib\weblogicaux.jar;d:\Weblogic\eval\cloudscape\lib\cloudscape.jar"
          >
          > JAVA_HOME= "d:\Weblogic\jre1_1"
          > WEBLOGIC_HOME="d:\Weblogic"
          > system properties:
          > weblogic.system.home=d:\Weblogic
          > java.compiler=symcjit
          >
          > ------->>>
          > weblogic.class.path=d:\Weblogic\license;d:\Weblogic\classes;d:\Weblogic\lib\weblogicaux.jar
          >
          > INITIAL_HEAP= 32 MB
          > MAX_HEAP= 32 MB
          > SERVERCLASSPATH=
          > ".;C:\wip\java\ejb\classes;d:\weblogic\jre1_1\lib\classes.zip;d:\weblogic\jre1_1\lib\rt.jar;d:\weblogic\classes\boot;d:\Weblogic\evel\cloudscape\lib\cloudscape.jar;d:\Weblogic\jre1_1\lib\classes.zip;d:\Weblogic\jre1_1\lib\rt.jar;d:\Weblogic\classes\boot;d:\Weblogic\eval\cloudscape\lib\cloudscape.jar"

How can I make a server differ between two or more clients?

How can I make a server differ between two or more clients?
The clients can connect and talk to the server fine, but how can I make the server talk to one, two or all clients? i.e. what would be a good way to implement this?
Currently, the server listens for connections like this:
while (listening) {
try {
new ServerThread(this, serverSocket.accept()).start();
I guess one way would be to add the ServerThreads to a Hashtable with the client ID as key, and then get the ServerThread with the proper client ID, but this seems unnecessary complicated. Any ideas?

Complicated was perhaps the wrong word, I should have
written something like it doesn't "feel" right. Or is
this a common and good way to solve communication
between a server and multiple clients?Thats pretty much how I do it. I normally use an array or ArrayList of Sockets instead of HashTable, with [0] being the first player etc.... Then you can communicate with exactly who you want. If you want to send bytes to all of them, just send the same thing to each socket individually (or is there a better way to do this?).

Hi this pandu can i know what is the diff between pnp &pnpce ldb

hi,
this pandu can i know what is the diff between pnp &pnpce logical database.
thanks and regards,
pandu.

pretty much the same.. except that PNPCE has additional functionality to deal with Concurrent Employment.. PL go through <a href="http://help.sap.com/saphelp_erp2005/helpdata/en/c6/8a15381b80436ce10000009b38f8cf/frameset.htm">SAP Help</a> for more info.
~Suresh

Can I switch back and forth the same sim card between an old iPhone 4 and a new one never used in order to activate the latter? Should I use same Apple Account?

Can I switch back and forth the same sim card between an old iPhone 4 and a new one never used in order to activate the latter? Should I use same Apple Account? Should I activate it via WiFi or iTunes? I am filtering on the MAC no and I cannot read that number from the new iPhone without having it activated??!!
All I want do is to have the new phone activated and then tested!
Ciao // Mufftas

Yes, you can do that.

Can a class b subclass of itself wh is diff between instaceof n isInstance

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