Newbie question about abstract methods

hey, I'm working on a web application that I was given and I'm a little confused about
some of the code in some of the classes. These are some methods in this abstract class. I don't understand
how this post method works if the method it's calling is declared abstract. Could someone please tell me how this works?
    public final Representation post(Representation entity, Variant variant) throws ResourceException {
        prePostAuthorization(entity);
        if (!authorizeGet()) {
            return doUnauthenticatedGet(variant);
        } else {
            return doAuthenticatedPost(entity, variant);
protected abstract boolean authorizeGet();Thanks
Edited by: saru88 on Aug 10, 2010 8:09 PM

Abstract Methods specify the requirements, but to Implement the functionality later.
So with abstract methods or classes it is possible to seperate the design from the implementation in a software project.
Abstract methods are always used together with extended classes, so I am pretty sure that you are using another class.
Btw: Please post the Code Keyword in these brackets:

Similar Messages

Which of the following are true about abstract methods in EJB 2.0

Hi guys I'm beginner to EJB and i got some unanswered questions.
Can any one of you please.. give answers?
Thanks if you do...
Which of the following are true about abstract methods in EJB 2.0
CMP?
Choose all correct answers:
1. Abstract accessor methods should not be exposed in the EJB
component's interface
2.Abstract accessor/mutator methods are used to access and modify
persistent state and relationship information for entity objects
3.Abstract Accessor/Mutator methods do not throw exceptions
4.The EJB developer must implement the Accessor/Mutator methods
5.Abstract accessor methods may or may not be exposed in the EJB
component's interface
2.Which ONE of the following is true?
Choose the best answer:
1.Local interfaces cannot have a relationship with other Entity
components
2.Local interfaces cannot be used for Stateless Session EJB
3.Local interfaces can be a part of Object's persistent state
4.Local interfaces have the same functionality as that of a
stateless Session EJB
3.Which of the following describe the <cmr-field> in a EJB 2.0
descriptor?
Choose all correct answers:
1.A Local interface/Entity can be a value of a <cmr-field>
2.There is no <cmr-field> in EJB 2.0 descriptor
3.It is used to represent one meaningful association between any
pair of Entity EJBs, based on the business logic of the Application
4.It provides a particular mapping from an object model to a
relational database schema
5.It allows the Local Entity interfaces to participate in
relationships
4.Which of the following are the advantages of using Local interfaces
instead of dependent value classes?
Choose all correct answers:
1.Local Entity Interfaces can participate in Relationships
2.The life cycle of Local Entity Interfaces is managed by EJB
container, intelligently
3.Local Entity Interfaces can be used in EJB QL Queries
4.Local Entity Interfaces can be a part of the <cmp-field> but not
<cmr-field>
5.Which of the following are true about Local interfaces
1.A local interface must be located in the same JVM to which the EJB
component is deployed
2.Local calls involve pass-by-reference.
3.The objects that are passed as parameters in local interface
method calls must be serializable.
4.In general, the references that are passed across the local
interface cannot be used outside of the immediate call chain and must
never be stored as part of the state of another enterprise bean.
6.Which of the following specifies the correct way for a client
to access a Message driven Bean?
Choose the best answer:
1. via a Remote interface
2. via Home interface
3. Message driven bean can be accessed directly by the client
4. both 1 & 2
5. none of the above
------------------------------------------------------------------------7.Which of the following statements are true about message-driven
bean Clients?
------------------------------------------------------------------------Choose all correct answers:
They can create Queue and QueueConnectionFactory objects
They can create Topic and TopicConnectionFactory objects
They can lookup the JNDI server and obtain the references for
Queue and Topic and their connection Factories
Only 1 and 2 above

Hi guys I'm beginner to EJB and i got some unanswered
questions.
Can any one of you please.. give answers?
Thanks if you do...
Which of the following are true about abstract methods
in EJB 2.0
CMP?
Choose all correct answers:
1. Abstract accessor methods should not be exposed
d in the EJB
component's interfacefalse
2.Abstract accessor/mutator methods are used to
access and modify
persistent state and relationship information for
entity objectstrue
>
3.Abstract Accessor/Mutator methods do not throw
exceptionstrue
>
4.The EJB developer must implement the
Accessor/Mutator methodsfalse
5.Abstract accessor methods may or may not be exposed
in the EJB
component's interfacetrue
2.Which ONE of the following is true?
Choose the best answer:
1.Local interfaces cannot have a relationship with
other Entity
componentsfalse
2.Local interfaces cannot be used for Stateless
Session EJBfalse
3.Local interfaces can be a part of Object's
persistent statefalse
4.Local interfaces have the same functionality as
that of a
stateless Session EJBtrue
3.Which of the following describe the <cmr-field> in a
EJB 2.0
descriptor?
Choose all correct answers:
1.A Local interface/Entity can be a value of a
<cmr-field>true
2.There is no <cmr-field> in EJB 2.0 descriptorfalse
3.It is used to represent one meaningful association
between any
pair of Entity EJBs, based on the business logic of
the Applicationtrue
4.It provides a particular mapping from an object
model to a
relational database schematrue
5.It allows the Local Entity interfaces to
participate in
relationshipstrue
4.Which of the following are the advantages of using
Local interfaces
instead of dependent value classes?
Choose all correct answers:
1.Local Entity Interfaces can participate in
Relationshipsis
2.The life cycle of Local Entity Interfaces is
managed by EJB
container, intelligentlyis
3.Local Entity Interfaces can be used in EJB QL
Queriesnot
4.Local Entity Interfaces can be a part of the
<cmp-field> but not
<cmr-field>not
>
>
5.Which of the following are true about Local
interfaces
1.A local interface must be located in the same JVM
M to which the EJB
component is deployedtrue
2.Local calls involve pass-by-reference.true
3.The objects that are passed as parameters in local
l interface
method calls must be serializable.false
4.In general, the references that are passed across
s the local
interface cannot be used outside of the immediate
e call chain and must
never be stored as part of the state of another
r enterprise bean.true
>
6.Which of the following specifies the correct way for
a client
to access a Message driven Bean?
Choose the best answer:
1. via a Remote interfacefalse
2. via Home interfacefalse
3. Message driven bean can be accessed directly by
the clientfalse
4. both 1 & 2false
5. none of the abovetrue.
>
----------------7.Which of the following statements
are true about message-driven
bean Clients?
----------------Choose all correct answers:
They can create Queue and QueueConnectionFactory
objectsthe container can, dunno bout clients
>
They can create Topic and TopicConnectionFactory
objectsthe container can, dunno bout clients
>
They can lookup the JNDI server and obtain the
references for
Queue and Topic and their connection Factories
true
Only 1 and 2 abovefalse
somebody correct me if i'm wrong

Misunderstanding about abstract methods

I think my compiler just taught me something, and after reading the JLS I concluded that I had a misconception about abstract methods. However, if someone could confirm this I would feel more comfortable.
I had defined a class structure like so:public abstract class Grandpa{
public abstract void do();
public abstract class Pa extends Grandpa {
public void do(){
// whatever
public class Child extends Pa {
}I got a compile error indicating that Child must implement do(). I had thought that since there was an implementation provided by Pa that Child didn't need to supply one, but I guess I was wrong. Right? :-)

Nested where? Inside Pa? Other? Static?Inside Pa.
It sounds like you're satisfied, but if you want to
continue the discussion, I'll make the standard
request. Come on, you know it, say it with me: Provide
a small, complete, working (in that it doesn't
compile) example that demonstrates this. :-)Yeah, that's exactly what I was working on for the bug report, but I can't get the compile error in my small example. Argh! I'll have to go back some time and build it up to match the other classes until I get the error, because I still get it consistently with the real thing. I have no idea what the key factor is, though - I've tried everything obvious and I don't have time to work through it right now.
No prob. It's a pleasant break from arguing with UJ.
:-)Glad I could offer you a distraction. :-) I'll post here again if I ever figure out what the deal is.

A question about a method with generic bounded type parameter

Hello everybody,
Sorry, if I ask a question which seems basic, but
I'm new to generic types. My problem is about a method
with a bounded type parameter. Consider the following
situation:
abstract class A{     }
class B extends A{     }
abstract class C
     public abstract <T extends A> T someMethod();
public class Test extends C
     public <T extends A> T someMethod()
          return new B();
}What I want to do inside the method someMethod in the class Test, is to
return an instance of the class B.
Normally, I'm supposed to be able to do that, because an instance of
B is also an instance of A (because B extends A).
However I cannot compile this program, and here is the error message:
Test.java:16: incompatible types
found   : B
required: T
                return new B();
                       ^
1 errorany idea?
many thanks,

Hello again,
First of all, thank you very much for all the answers. After I posted the comment, I worked on the program
and I understood that in fact, as spoon_ says the only returned value can be null.
I'm agree that I asked you a very strange (and a bit stupid) question. Actually, during recent months,
I have been working with cryptography API Core in Java. I understood that there are classes and
interfaces for defining keys and key factories specification, such as KeySpec (interface) and
KeyFactorySpi (abstract class). I wanted to have some experience with these classes in order to
understand them better. So I created a class implementing the interface KeySpec, following by a
corresponding Key subclass (with some XOR algorithm that I defined myself) and everything was
compiled (JDK 1.6) and worked perfectly. Except that, when I wanted to implement a factory spi
for my classes, I saw for the first time this strange method header:
protected abstract <T extends KeySpec> T engineGetKeySpec
(Key key, Class<T> keySpec) throws InvalidKeySpecExceptionThat's why yesterday, I gave you a similar example with the classes A, B, ...
in order to not to open a complicated security discussion but just to explain the ambiguous
part for me, that is, the use of T generic parameter.
The abstract class KeyFactorySpi was defined by Sun Microsystem, in order to give to security
providers, the possibility to implement cryptography services and algorithms according to a given
RFC (or whatever technical document). The methods in this class are invoked inside the
KeyFactory class (If you have installed the JDK sources provided by Sun, You can
verify this, by looking the source code of the KeyFactory class.) So here the T parameter is a
key specification, that is, a class that implements the interface KeySpec and this class is often
defined by the provider and not Sun.
stefan.schulz wrote:
>
If you define the method to return some bound T that extends A, you cannot
return a B, because T would be declared externally at invocation time.
The definition of T as is does not make sense at all.>
He is absolutely right about that, but the problem is, as I said, here we are
talking about the implementation and not the invocation. The implementation is done
by the provider whereas the invocation is done by Sun in the class KeyFactory.
So there are completely separated.
Therefore I wonder, how a provider can finally impelment this method??
Besides, dannyyates wrote
>
Find whoever wrote the signature and shoot them. Then rewrite their code.
Actually, before you shoot them, ask them what they were trying to achieve that
is different from my first suggestion!
>
As I said, I didn't choose this method header and I'm completely agree
with your suggestion, the following method header will do the job very well
protected abstract KeySpec engineGetKeySpec (Key key, KeySpec key_spec)
throws InvalidKeySpecException and personally I don't see any interest in using a generic bounded parameter T
in this method header definition.
Once agin, thanks a lot for the answers.

Newbie Question about FM 8 and Acrobat Pro 9

Hello:
I have some dcouments that I've written in FM v8.0p277. I print them to PDF so that I can have a copy to include on a CD and I also print some hard copies.
My newbie question is whether there is a way to create a PDF for hard copy where I mainitain the colors in photos and figures but that the text that is hyperlinked doesn't appear as blue. I want to keep the links live within the soft copy. Is there something I can change within Frame or with Acrobat?
TIA,
Kimberly

Kimberly,
How comes the text is blue in the first place? I guess the cross-reference formats use some character format which makes them blue? There are many options:
Temporarily change the color definition for the color used in the cross-reference format to black.
Temporarily change the character format to not use that color.
Temporarily change the cross-reference definition to not used that character format.
Whichever method you choose, I would create a separate document with the changed format setting and import those format into your book, create the PDF and then import the same format from the official template.
- Michael

Question about abstract classes and instances

I have just read about abstract classes and have learned that they cannot be instantiated.
I am doing some exercises and have done a class named "Person" and an abstract class named "Animal".
I want to create a method in "Person" that makes it possible to set more animals to Person objects.
So I wrote this method in class Person and compiled it and did not get any errors, but will this work later when I run the main-method?
public void addAnimal(Animal newAnimal)
animal.add(newAnimal);
}Is newAnimal not an instance?

Roxxor wrote:
Ok, but why is it necessary with constructors in abstract classes if we don�t use them (because what I have understand, constructors are used to create objects)?Constructors don't create objects. The new operator creates objects. An object's c'tor is invoked after the object has already been created. The c'tors job is to initialize the newly-created object to a valid state. Whenever a child object is created, the parent's c'tor is run before the child's c'tor, so that by the time we're inside the child's c'tor, setting up the child's state, we know that the parent (or rather the "parent part" of the object we're initializing) is in a valid state.
Constructor rules:
1) Every class has at least one ctor.
1.1) If you do not define an explicit constructor for your class, the compiler provides a implicit constructor that takes no args and simply calls super().
1.2) If you do define one or more explicit constructors, regardless of whether they take args, then the compiler no longer provides the implicit no-arg ctor. In this case, you must explicitly define a public MyClass() {...} if you want one.
1.3) Constructors are not inherited.
2) The first statement in the body of any ctor is either a call to a superclass ctor super(...) or a call to another ctor of this class this(...) 2.1) If you do not explicitly put a call to super(...) or this(...) as the first statement in a ctor that you define, then the compiler implicitly inserts a call to super's no-arg ctor super() as the first call. The implicitly called ctor is always super's no-arg ctor, regardless of whether the currently running ctor takes args.
2.2) There is always exactly one call to either super(...) or this(...) in each constructor, and it is always the first call. You can't put in more than one, and if you put one in, the compiler's implicitly provided one is removed.

About abstract method read() in class InputStream (third message)

The subclass FilterInputStream is not abstract and extend InputStream: have you ever seen the implementation of that method in the source code available in SDK? It only calls that abstract method!!! I think it is not a very simple problem and anyway the answer is not in my diffrent books. Thanks for your non trivial answer.

Please post this as a "reply" in your original thread
http://forum.java.sun.com/thread.jspa?threadID=5192979&tstart=0
Don't start a new thread, simply reply to one of the other posts in the original thread (there is a button "reply" on the right hand side).

Newbie question about loading servlets on tomcat

I have what is probably a very basic question about loading simple servlets on to tomcat to test its installation. I have followed instructions from numerous tutorials to the letter but still I can't get it to work.
I have installed tomcat on win2k in c:\tomcat. I set up the jdk, environment vars (JAVA_HOME, CATALINA_HOME, TOMCAT_HOME) which all point at the correct dirs. I can compile a servlet without errors. I can also place a test jsp and html file into the root directory and they both work fine.
However, now I am trying a test servlet and no matter what I do it gives me a 404. I have a servlet class file called "HelloServlet.class" which I placed into the %install_dir%\webapps\ROOT\WEB-INF\classes directory. I try to reference it using this url:
http://localhost/servlet/HelloServlet
Tomcat is configured to use port 80 and has been restarted after adding the servlet class file. Does anyone have a clue why this is not working for me?
Many thanks
Marc

You have to add in the web.xml file that it is in the WEB-INF dir, the information about your servlet. An example:
<web-app>
<servlet>
<servlet-name>HelloServlet</servlet-name>
<servlet-class>HelloServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>HelloServlet</servlet-name>
<url-pattern>/HelloServlet</url-pattern>
</servlet-mapping>
</web-app>

About abstract method

Hi, there are many abstract methods In the abstract java.awt.Graphics class. when I write a class extends Component(for example JPanel), override the paint(Graphics g) method, then I can invoke the abstract methods in the Graphics class to draw in my Component.
So I think there is a class extends the Grahpics class, but is secret to us. and the JDK designer how to design these class structor?
Thanks a lot,
Regards.

The reason that why most of the methods of the Graphics class are abstract is because to have an implementation for them, the underlying platform must be used, for example: g.drawLine(0,0,100,100) would on Linux end up on the native side making the call:
XDrawLine(display,drawable,gc,0,0,100,100);whereas on Windows it would be something else. There is not platform independent way to draw on the screen.
Tuomas Rinta

Newbie question about saving files

Hi all,
A newbie question here, and maybe it is a dumb question, but I can't get my head around this and sofar found no answer in the forums here.
When I save a file on my macbook, I can only save it to "top" folders.
What I mean is I try to save a file for instance to documents/worddocs/lyrics just to say something, then I have to save the file first to documents, and the move it to the lyrics folder via finder or move it to :worddocs folder and then move it again to the lyrics folder. Hope you still get my drift here
Is there a way to just save it to the subfolders without going through all this moving around?
Thanks in advance for any advice
Peter

When you click File>Save As, you will see the Save As window pop up. At the top, you will see a box entitled Save As, which has a space for your to enter the file name. To the right of this box is an arrow pointing down. Click it. The full file hierarchy will be seen. Then you can save directly to the file you want.
Hope this helps.
Don

2 newbies question about diskgroups

Hi gurus,
I have 2 newbies question:
Im working in a RAC Database (11.2.0.3) on Redhat 5.3 with some disk groups. One of this groups have 6 disks on it with different space (134, 236G, 236G, 185G, 185G and 185G).
My questions are:
1) What would be happend when the lower space disk will be full?
2) At this moment the diskgroups are at 45% so i was thinking to change their spaces to have all with the same space (around 193G each), it would create any problem? i should restart database or can do it with database up?
Thanks

if a disk is filled, what would happen? could i resize the disks with same size without stop database and without affecting the data stored within each disc?
By the word 'disk' I assume you mean LUN . When a LUN in a disk group is filled, ASM will use the remaining LUNs to store the data. You should always use LUNs of uniform size to avoid uneven I/O .
could i resize the disks with same size without stop database and without affecting the data stored within each disc
You can get the Unix/Storage team to allocate more LUNs for this Server. Once these LUNs are added , check if the following pre-reqs are met for the LUN which is yet to be added to the disk group
v$asm_disk.HEADER_STATUS = 'CANDIDATE'
v$asm_disk.PATH = /dev/rdsk/youLUNname
v$asm_disk.NAME will be NULL
Now you can add the LUNs using
alter diskgroup DATA_DG01 add disk '/dev/rdsk/youLUNname' rebalance power 4 ; wait for rebalance to finish (check status in V$ASM_OPERATION)
Yes. The above can be done without stopping the DB. It won't affect the stored data either.

Two (too much?) newbies questions about KT3 Ultra 2

Goodmorning all.
I've bought a KT3 Ultra2 (MS-6380E) motherboard and i've two questions about it.
First of all I need to buy the optional S-Bracket to use my SPDif sound sistem... where can i buy it in Italy or in Internet?
In second i've to know the highest processor my MB support becouse i have to upgrade my PC.
Can U help me?
Tha a lot and sorry for disturb.
Hallo.

Hello,
question 2, not sure about question 1,
http://www.msi.com.tw/program/products/mainboard/mbd/pro_mbd_cpu_support_detail.php?UID=341&kind=1
You may need this BIOS update too.
http://www.msi.com.tw/program/support/bios/bos/spt_bos_detail.php?UID=341&kind=1

Please, help a newbie: Question about animating expanding containers

Hi All,
Short Version of my Question:
I'm making a media player that needs to have an animation for panels sliding up and down and left and right, and the method I've been using to do this performs far slower than the speed I believe is possible, and required. What is a fast way to make a high performance animation for such an application?
Details:
So far, to do the animation, I've been using JSplitPanes and changing the position of the divider in a loop and calling paintImmediately or paintDirtyRegion like so:
public void animateDividerLocation( JSplitPane j, int to, int direction) {
for(int i=j.getDividerLocation(); i>=to; i-=JUMP_SIZE) {
j.setDividerLocation(i);
j.validate();
j.paintImmediately(0, 0, j.getWidth(), j.getHeight());
The validate and paintImmediately calls have been necessary to see any changes while the loop is going. I.e., if those calls are left out, the components appear to just skip right to where they were supposed to animate to, without having been animated at all.
The animation requirement is pretty simple. Basically, the application looks like it has 3 panels. One on the right, one on the left, and a toolbar at the bottom. The animation just needs to make the panels expand and contract.
Currenly, the animation only gets about, say, 4 frames a second on the 800 MHz Transmeta Crusoe processor, 114 MB Ram, Windows 2000 machine I must use (to approximate the performance of the processor I'll be using, which will run embedded Linux), even though I've taken most of the visible components out of the JPanels during the animation. I don't think this has to do with RAM reaching capacity, as the harddrive light does not light up often. Even if this were the case, the animation goes also goes slow (about 13 frames a second) on my 3 GHz P4 Windows XP if I keeps some JButtons, images etc., inside the JPanels. I get about 50 frames/sec on my 3 GHz P4, if I take most of the JButtons out, as I do for the 800 MHz processor. This is sufficient to animate the panels 400 pixels across the screen at 20 pixels per jump, but it isn't fast or smooth enough to animate across 400 pixels moving at 4 pixel jumps. I know 50 frames/sec is generally considered fast, but in this case, there is hardly anything changing on the screen (hardly any dirty pixels per new frame) and so I'd expect there to be some way to make the animation go much faster and smoother, since I've seen games and other application do much more much faster and much smoother.
I'm hoping someone can suggest a different, faster way to do the animation I require. Perhaps using the JSplitPane trick is not a good idea in terms of performance. Perhaps there are some tricks I can apply to my JSplitPane trick?
I haven't been using any fancy tricks - no double buffering, volatile images, canvas or other animation speed techniques. I haven't ever used any of those things as I'm fairly new to Swing and the 2D API. Actually I've read somewhere that Swing does double buffering without being told to, if I understood what I read. Is doing double buffering explicitly still required? And, if I do need to use double buffering or canvas or volatile images or anything else, I'm not sure how I would apply those techiniques to my problem, since I'm not animating a static image around the screen, but rather a set of containers (JSplitPanes and JPanels, mostly) and components (mostly JButtons) that often get re-adjusted or expanded as they are being animated. Do I need to get the Graphics object of the top container (would that contain the graphics objects for all the contained components?) and then double buffer, volatile image it, do the animation on a canvas, or something like that? Or what?
Thanks you SO much for any help!
Cortar
Related Issues(?) (Secondary concerns):
Although there are only three main panels, the actual number of GUI components I'm using, during the time of animation, is about 20 JPanels/JSplitPanes and 10 JButtons. Among the JPanels and the JSplitPanes, only a few JPanels are set to visible. I, for one, don't think this higher number of components is what is slowing me down, as I've tried taking out some components on my 3GHz machine and it didn't seem to affect performance much, if any. Am I wrong? Will minimizing components be among the necessary steps towards better performance?
Anyhow, the total number of JContainers that the application creates (mostly JPanels) is perhaps less than 100, and the total number of JComponents created (mostly JButtons and ImageIcons) is less than 200. The application somehow manages to use up 50 MBs RAM. Why? Without looking at the code, can anyone offer a FAQ type of answer to this?

You can comment out the lines that add buttons to the panels to see the behavior with empty panels.
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.Timer;
public class DancingPanels
    static GridBagLayout gridbag = new GridBagLayout();
    static Timer timer;
    static int delay = 40;
    static int weightInc = 50;
    static boolean goLeft = false;
    public static void main(String[] args)
        final GridBagConstraints gbc = new GridBagConstraints();
        gbc.weightx = 1.0;
        gbc.weighty = 1.0;
        gbc.fill = gbc.HORIZONTAL;
        final JPanel leftPanel = new JPanel(gridbag);
        leftPanel.setBackground(Color.blue);
        gbc.insets = new Insets(0,30,0,30);
        leftPanel.add(new JButton("1"), gbc);
        leftPanel.add(new JButton("2"), gbc);
        final JPanel rightPanel = new JPanel(gridbag);
        rightPanel.setBackground(Color.yellow);
        gbc.insets = new Insets(30,50,30,50);
        gbc.gridwidth = gbc.REMAINDER;
        rightPanel.add(new JButton("3"), gbc);
        rightPanel.add(new JButton("4"), gbc);
        final JPanel panel = new JPanel(gridbag);
        gbc.fill = gbc.BOTH;
        gbc.insets = new Insets(0,0,0,0);
        gbc.gridwidth = gbc.RELATIVE;
        panel.add(leftPanel, gbc);
        gbc.gridwidth = gbc.REMAINDER;
        panel.add(rightPanel, gbc);
        timer = new Timer(delay, new ActionListener()
                gbc.fill = gbc.BOTH;
                gbc.gridwidth = 1;
            public void actionPerformed(ActionEvent e)
                double[] w = cycleWeights();
                gbc.weightx = w[0];
                gridbag.setConstraints(leftPanel, gbc);
                gbc.weightx = w[1];
                gridbag.setConstraints(rightPanel, gbc);
                panel.revalidate();
                panel.repaint();
        JFrame f = new JFrame("Dancing Panels");
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(panel);
        f.setSize(400,300);
        f.setLocation(200,200);
        f.setVisible(true);
        timer.start();
    private static double[] cycleWeights()
        if(goLeft)
            weightInc--;
        else
            weightInc++;
        if(weightInc > 100)
            weightInc = 100;
            goLeft = true;
        if(weightInc < 0)
            weightInc = 0;
            goLeft = false;
        double wLeft = weightInc/ 100.0;
        double wRight = (100 - weightInc)/100.0;
        return new double[]{wLeft, wRight};
}

About abstract method read() in class InputStream (second message)

I know but my question needs other arguments. When the Java virtual machine must help me in reading some input stream, I imagine it uses some calls to the operating system: I would like to know if behind that method there is something which seems a system call even if is abstract and so without apparently code.

Please post this as a "reply" in your original thread
http://forum.java.sun.com/thread.jspa?threadID=5192979&tstart=0
Don't start a new thread, simply reply to one of the other posts in the original thread (there is a button "reply" on the right hand side).

About abstract method read() in class InputStream

I would like to know if behind the method
public abstract int read() throws IOException
in the abstract class InputStream there is some code that
is called when I have to read a stream. In this case where can I find
something about this code and, if is written in other languages, why
is not present the key word native?
Thanks for yours answers and sorry for my bad english.

Ciao Matteo.
Scusa se ti rispondo in ritardo... ma ero in pausa pranzo.
Chiedimi pure qualcosa di pi? specifico e se posso darti una mano ti rispondo.
Le classi astratte sono utilizzate per fornire un comportamento standard lasciando per? uno o pi? metodi non implementati... liberi per le necessit? implementative degli utilizzatori.
Nel caso specifico la classe InputStream ? una classe astratta che lascia non implementato il metodo read(). Tu nel tuo codice non utilizzerai mai questa classe come oggetto, ma nel caso specifico una sua sottoclasse che ha implementato il metodo read().
Se vai nelle api di InputStream vedrai che ci sono diverse sottoclassi che estendono InputStream. Guarda ad esempio il codice di ByteArrayInputStream: in questa classe il metodo read() non ? nativo ma restituisce un byte appartenente al suo array interno.
I metodi nativi (ad esempio il metodo read() della classe FileInputStream) non hanno implementazione java ma fanno invece riferimento a delle chiamate dirette al sistema operativo.
Per quanto riguarda la classe FilterInputStream di cui parlavi: essa nel suo costruttore riceve un InputStream. Questo significa che si deve passare nel costruttore non la classe InputStream (che ? astratta) ma una classe che la estende e che quindi non sia astratta. Il motivo per il quale FilterInputStream faccia riferimento a una classe di tipo InputStream al suo interno, ? che in java gli stream di input e di output possono essere composti l'uno sopra l'altro per formare una "catena" (a tal proposito vedi per maggiori dettagli uno dei tani articoli che si trovano in rete.... ad esempio ti indico questo http://java.sun.com/developer/technicalArticles/Streams/ProgIOStreams/). Comunque per dirla in due parole: tu puoi voler usare un FileInputStream per leggere un file, ma se hai bisogno di effettuare una lettura pi? efficiente (quindi bufferizzata) puoi aggiungere in catena al FileInputStream un oggetto di tipo FilterInputStream (nel caso specifico un BufferedInputStream che non ? altro che una sottoclasse di FilterInputStream).
Spero di aver chiarito qualche tuo dubbio!
Ciao
Diego

Newbie question about abstract methods

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