Java

Re: interacting with parent

2-Aug-12 20:40

Are you sure this is java? Looks more like javascript.

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JR2122-Aug-12 21:09

JR212

2-Aug-12 21:09

Your right. It's javascript. I didn't know there is another forum for javascript. However I found it after days of looking I posted the question and today I found that I must use 'window.opener.document'

Jan

PS: If there is an admin he/she may move the message to the correct forum Smile | :)

Re: interacting with parent

Nagy Vilmos2-Aug-12 21:19

Thorwing Exception to the calling function from other class

2-Aug-12 21:19

Okay. The admins may or may not move this, it depends on getting them sober enough for long enough. Big Grin | :-D

BTW, I did not 1 vote your question, I will counter it as it is not deserved.

I want help

Mohammed Kherfan1-Aug-12 22:47

Mohammed Kherfan

1-Aug-12 22:47

hello

I wanna make session between two field in code .bsh (BeanShell) : is sample java code

Internet pages contain the same field Example: Field Name
When entering values in the first field in the first page and move on to the second page must be entered the same values found in the other the right

please i want that code ???

Re: I want help

Andrei Straut1-Aug-12 23:03

Andrei Straut

1-Aug-12 23:03

I want the code to generate everything I need for the project I'm working on, but that doesn't mean I'll get it.

Try to rephrase the question as a first step to make it clearer (I don't understand very much of what you're asking to be honest). And as a second step, try at least to come up with a solution all by yourself, post what you've come up with, and where you got stuck. People will try to help you, but only if you show that you're willing to help yourself.

In the current form of your question, you're highly unlikely to get an answer.

Full-fledged Java/.NET lover, full-fledged PHP hater.
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modified 2-Aug-12 7:03am.

muhammed_k31-Jul-12 23:00

Re: Throwing Exception to the calling function from other class

31-Jul-12 23:00

Hai,can any one help me in this querry.

I am calling a function 'A' which is in a class 'CA', from a function 'B' which is in the Class 'CB'.If there is any exception produced in function 'A' it will generate an error code(intiger Value)in Catch block.How can i get that error code from the Function A to function B only if the exception had occured.

Sniff | :^)

Andrei Straut31-Jul-12 23:38

Andrei Straut

31-Jul-12 23:38

If the error code generated by method A on exception is unique (meaning that no normal output from A will ever match that error code), you can simply do this (assuming that error code returned on exception is -1):

Java

if(ca.A() == -1) {
    //Do stuff when exception occurred
}

Conversely, if you have access to the sources and you are allowed to modify them, don't catch the exception. Modify the CA.A() method signature and add throws ExceptionThrownFromCA (just an example). Like this, you don't even need to check the error code, and you can do this:

Java

public void B() {
    CA ca = new CA();

    try {
        ca.A();
    } catch(ExceptionThrownFromCA e) {
        //Do your stuff
    }
}

Full-fledged Java/.NET lover, full-fledged PHP hater.
Full-fledged Google/Microsoft lover, full-fledged Apple hater.
Full-fledged Skype lover, full-fledged YM hater.

modified 1-Aug-12 10:07am.

Re: Thorwing Exception to the calling function from other class

Nagy Vilmos1-Aug-12 20:08

Re: Thorwing Exception to the calling function from other class

1-Aug-12 20:08

Further to the earlier answer:

0. There are no functions. In the OO world, an object supports methods and, in some cases but not Java, properties.

1. If a class throws an exception it must declare it in it's signature:

Java

void methodName() throws MethodException {
    ...
}

2. An exception is not an error. An exception should be used when you don't know what to do or cannot continue processing. As an example, if you insert a row into a table and it violates a unique constraint then that is an exception. If you try to read a value from a table and it does not exist that is an error.

3. It is advisable to not use an exception to pass results. The choice should be that if an exception is thrown the calling method defaults a result or the called method's return values must include an error range.

muhammed_k2-Aug-12 6:43

Re: Thorwing Exception to the calling function from other class

2-Aug-12 6:43

Thankyou for your reply .

So what you suggest to do for the above case

Nagy Vilmos2-Aug-12 20:23

Re: Thorwing Exception to the calling function from other class

2-Aug-12 20:23

I do not have your code so I cannot possibly say which way is better, that is up to the implementation. If the called method knows what to do irrespective of the caller then the exception should not be thrown up the stack.

muhammed_k2-Aug-12 21:19

Re: Thorwing Exception to the calling function from other class

2-Aug-12 21:19

Can i make that error code variable as global and when ever i am calling any fuction after that itself i will access the error code and check it.

Nagy Vilmos2-Aug-12 21:48

Re: Thorwing Exception to the calling function from other class

2-Aug-12 21:48

There is no such thing as 'global' in java.

One approach is to have an error state within a class, but this may not be appropriate. I would suggest that if you need to have a return code AND an exception then you can always return a composite class:

Java

public class ReturnState {
    private final int code;
    private final String description;
    private final Object object;
    private final Exception exception;

    public ReturnState (int code,
            String description,
            Object object,
            Exception exception) {
        this.code = code;
        this.description = description;
        this.object = object;
        this.exception = exception;
    }

    public int getCode() {
        return this.code;
    }

    public Exception getException() {
        return this.exception;
    }

    ...
}

That said, it is rare that you need BOTH so either have the return codes include errors or use exceptions.

muhammed_k2-Aug-12 21:55

access data stored in hashset java

2-Aug-12 21:55

k Got it thanks a lot, i will return the exception,according to the exception i will generate the error code in my calling function. Smile | :)

ahmadiss31-Jul-12 1:56

ahmadiss

31-Jul-12 1:56

I work with jee and JSF2.0 and hibernate

I want to access my data in my xhtml page my data are stored in hashset in the managedBean

I don't find how to access this data in html

in java I use this :

public void SaveCommande(Commande c) {

    try {
        org.hibernate.Transaction tx = session.beginTransaction();
        session.save(c);
        Iterator it = c.getFichiers().iterator();
            while(it.hasNext())
                session.save((Fichier)it.next());
        tx.commit();
    } catch (Exception e) {
        e.printStackTrace();
    }
}

do you have any idea

error when run project jsf2.0

ahmadiss30-Jul-12 7:14

ahmadiss

30-Jul-12 7:14

I have this error when I run my project jsf2.0

Java

Avertissement: StandardWrapperValve[Faces Servlet]: PWC1406: Servlet.service() for servlet Faces Servlet threw exception
java.lang.NullPointerException
	at com.sun.enterprise.v3.services.impl.monitor.MonitorableSelectionKeyHandler$CloseHandler.notifyClosed(MonitorableSelectionKeyHandler.java:94)
	at com.sun.enterprise.v3.services.impl.monitor.MonitorableSelectionKeyHandler$CloseHandler.remotlyClosed(MonitorableSelectionKeyHandler.java:90)
	at com.sun.grizzly.BaseSelectionKeyHandler.notifyRemotlyClose(BaseSelectionKeyHandler.java:233)
	at com.sun.grizzly.util.OutputWriter.notifyRemotelyClosed(OutputWriter.java:353)
	at com.sun.grizzly.util.OutputWriter.flushChannel(OutputWriter.java:148)
	at com.sun.grizzly.util.OutputWriter.flushChannel(OutputWriter.java:76)
	at com.sun.grizzly.http.SocketChannelOutputBuffer.flushChannel(SocketChannelOutputBuffer.java:326)
	at com.sun.grizzly.http.SocketChannelOutputBuffer.flushBuffer(SocketChannelOutputBuffer.java:398)
	at com.sun.grizzly.http.SocketChannelOutputBuffer.endRequest(SocketChannelOutputBuffer.java:389)
	at com.sun.grizzly.http.ProcessorTask.action(ProcessorTask.java:1090)
	at com.sun.grizzly.tcp.Response.action(Response.java:268)
	at com.sun.grizzly.tcp.Response.finish(Response.java:412)
	at org.apache.catalina.connector.OutputBuffer.close(OutputBuffer.java:341)
	at org.apache.catalina.connector.CoyoteOutputStream.close(CoyoteOutputStream.java:187)
	at java.nio.channels.Channels$WritableByteChannelImpl.implCloseChannel(Channels.java:469)
	at java.nio.channels.spi.AbstractInterruptibleChannel.close(AbstractInterruptibleChannel.java:115)
	at com.sun.faces.application.resource.ResourceHandlerImpl.handleResourceRequest(ResourceHandlerImpl.java:296)
	at javax.faces.application.ResourceHandlerWrapper.handleResourceRequest(ResourceHandlerWrapper.java:125)
	at org.primefaces.application.PrimeResourceHandler.handleResourceRequest(PrimeResourceHandler.java:85)
	at javax.faces.webapp.FacesServlet.service(FacesServlet.java:591)
	at org.apache.catalina.core.StandardWrapper.service(StandardWrapper.java:1539)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:343)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
	at org.primefaces.webapp.filter.FileUploadFilter.doFilter(FileUploadFilter.java:79)
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:256)
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:217)
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:279)
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:175)
	at org.apache.catalina.core.StandardPipeline.doInvoke(StandardPipeline.java:655)
	at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:595)
	at com.sun.enterprise.web.WebPipeline.invoke(WebPipeline.java:98)
	at com.sun.enterprise.web.PESessionLockingStandardPipeline.invoke(PESessionLockingStandardPipeline.java:91)
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:162)
	at org.apache.catalina.connector.CoyoteAdapter.doService(CoyoteAdapter.java:330)
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:231)
	at com.sun.enterprise.v3.services.impl.ContainerMapper.service(ContainerMapper.java:174)
	at com.sun.grizzly.http.ProcessorTask.invokeAdapter(ProcessorTask.java:828)
	at com.sun.grizzly.http.ProcessorTask.doProcess(ProcessorTask.java:725)
	at com.sun.grizzly.http.ProcessorTask.process(ProcessorTask.java:1019)
	at com.sun.grizzly.http.DefaultProtocolFilter.execute(DefaultProtocolFilter.java:225)
	at com.sun.grizzly.DefaultProtocolChain.executeProtocolFilter(DefaultProtocolChain.java:137)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:104)
	at com.sun.grizzly.DefaultProtocolChain.execute(DefaultProtocolChain.java:90)
	at com.sun.grizzly.http.HttpProtocolChain.execute(HttpProtocolChain.java:79)
	at com.sun.grizzly.ProtocolChainContextTask.doCall(ProtocolChainContextTask.java:54)
	at com.sun.grizzly.SelectionKeyContextTask.call(SelectionKeyContextTask.java:59)
	at com.sun.grizzly.ContextTask.run(ContextTask.java:71)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.doWork(AbstractThreadPool.java:532)
	at com.sun.grizzly.util.AbstractThreadPool$Worker.run(AbstractThreadPool.java:513)
	at java.lang.Thread.run(Thread.java:722)

do you have an idea

thanks

Re: error when run project jsf2.0

Nagy Vilmos30-Jul-12 23:50

30-Jul-12 23:50

You are trying to invoke a method on an object that is referencing nothing.

Use the debug Luke.

Designing to interfaces?

Neo1010129-Jul-12 9:52

Neo10101

29-Jul-12 9:52

I have just heard about the 'Designing to Interfaces' concept.

I am required to implement this design methodology very soon, but I am not fully sure how it works.

What I learned so far is this:

Example A
-------------

Here, using a ShapeInterface decouples this Main app from any subshape object (Rectangle, Triangle, etc.).
So if I need to add a Shape type object in the future, I don't have to modify the client code because it's been 'coded to the interface'.
I only have to change the actual implementation in the concrete class itself.

Java

ShapeInterface shape = ShapeFactory.getNewInstance("triangle");
shape.draw();

Example B
-------------

This code is easy to break because this Main app will be tightly coupled to every future shape object I need (if there comes a Rectangle, I will need to change the code to instantiate a Rectangle etc.).
Also, the implementations are different and so I have to apply the appropriate implementation (Rectangle.draw(), Triangle.draw(), etc.)

Java

Triangle triangle = ShapeFactory.getNewInstance("triangle");
triangle.draw();

I understood this concept. Using an interface so that you won't have the change the code that uses the underlying concrete classes. Ok, understandable. I see the advantage.

Here's the concept that [b]I don't understand[/b]:

Example C
-------------

This example illustrates composition instead of inheritance (Object A has an Object B rather than IS-A B).
A can't print directly, it has to delegate to B. Fine, I understand that. What I don't understand is the advantage of this.

Couple of questions:

1) How was it decoupled?
2) Will putting the interface in between A and B decouple their relationship?
3) What if there was no interface between them? Then A would be tightly coupled to B?
4) If B disappears, can I simply replace it with a C class thanks to the interface?

If I don't understand these concepts then I can't move on in my design.

Java

public interface ABInterface {
    public void print();
}

public class A implements ABInterface {
    private B b;

    public A() {
        b = new B();
    }

    public void print() {
        b.print();
    }
}


public class B implements ABInterface {
    public void print(){
        System.out.println("Testing B");
    }
}

Ok, so that's that. However, I have another big problem:

Say I have a couple of classes that implement a particular interface. Now say that later, there is one method in that interface that I don't need anymore and thus need to delete.
Then it will cause a ripple-effect to the classes that implemented that interface because the implementation won't be correct anymore.

How do I avoid/deal with this?

It's quite a problem..
Any ideas on this?

BobJanova29-Jul-12 23:01

BobJanova

29-Jul-12 23:01

Composition allows you to switch the internal implementation of an interface easily. In your example you can easily change A so that it delegates to a new class X instead of B, and the client code won't notice (not even to change a new A() to new X(), or a DI container registration, as with inheritance). You can even write A so that it chooses a different internal implementation class at runtime (for example a file access wrapper which uses a local disk mapper, a memory mapper or a network resource mapper depending on what is passed to a constructor).

Unlike an inherited solution, the class B is totally decoupled from the class which uses A. B can be package-visible, if it's in the same package as A (in .Net it can and probably should be internal).

B won't be decoupled from A as long as A contains a 'new B()' type statement. You can, of course, use the normal interface and DI or factory mechanisms to decouple them, but you have to ask yourself what the purpose of that is, considering that A itself is already little more than a decoupling wrapper class (decoupling B from the outside world).

If you find that a method on an interface isn't used any more, if you're using a decent IDE you can chase down all the implementations in subclasses and remove them as well. Alternatively, if you use @Override annotations, when you remove the interface method, the implementers' methods with @Override will cause a compilation failure (because they're now not overriding anything) and you can go and delete them.

Neo1010129-Jul-12 23:48

Neo10101

29-Jul-12 23:48

Well, an IDE shouldn't make up for my design mistakes. I do use @Override annotations (Ant). Going on and deleting each single implementation is not the right way to work. I suppose that if a change in my code (removing a method) causes a waterfall effect (change implementation everywhere) then my code is badly written.

BobJanova30-Jul-12 0:13

BobJanova

30-Jul-12 0:13

Discovering that you don't actually need something you thought you did can be a sign of over-design. But we all have to rework and modify our designs as we code – that's fine and a natural part of software development.