Posts by Slavi

Here is a hint ... the first one in a) , when a number has !, it defines the factorial of a number, for example lets look at 5!
5! = 1*2*3*4*5

so in order to get !1+!2 ..etc , you need to define a method that computes the factorial for any number and then call it for the numbers that you re required such as

result = fact(1) + fact(2) + fact(3)+fact(4)+fact(5);

I am really stuck with this trying to implement it ... I am back to hello world application ... It runs perfectly fine if called from Terminal, completley goes nuts if called from Eclipse ......

Here is the entire code that I am using ...

RMI Interface:

import java.rmi.Remote;
import java.rmi.RemoteException;


public interface Hello extends Remote {
    public String sayHello() throws RemoteException;
}

RMI Server

import java.rmi.RemoteException;
import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;
import java.rmi.server.UnicastRemoteObject;
import javax.rmi.ssl.SslRMIClientSocketFactory;
import javax.rmi.ssl.SslRMIServerSocketFactory;

public class HelloImpl extends UnicastRemoteObject implements Hello {
    public HelloImpl() throws RemoteException {
        super(0, new SslRMIClientSocketFactory(), new SslRMIServerSocketFactory());
        LocateRegistry.createRegistry(3000);
        System.out.println("RMI registry running on port 3000");
    }
    public String sayHello() {
        return "Hello World!";
    }
    public static void main(String args[]) throws Exception {
        System.setProperty("javafx.net.ssl.keyStore","C:\\Users\\Slavi\\workspace\\rmiSSL\\keystore");
        System.setProperty("javafx.net.ssl.keyStorePassword","password");
        // Get reference to the RMI registry running on port 3000 in the local host
        Registry registry = LocateRegistry.getRegistry(null, 3000);
        // Bind this object instance to the name "HelloServer"
        HelloImpl obj = new HelloImpl();
        registry.bind("HelloServer", obj);
        System.out.println("HelloServer bound in registry");
    }
}

RMI Client

import java.rmi.registry.LocateRegistry;
import java.rmi.registry.Registry;

public class HelloClient {
    public static void main(String args[]) throws Exception {
        System.setProperty("javafx.net.ssl.trustStore","C:\\Users\\Slavi\\workspace\\rmiSSL\\truststore");
        System.setProperty("javafx.net.ssl.trustStorePassword","trustword");
        // Get reference to the RMI registry running on port 3000 in the local host
        Registry registry = LocateRegistry.getRegistry(null, 3000);
        // Lookup the remote reference bound to the name "HelloServer"
        Hello obj = (Hello) registry.lookup("HelloServer");
        String message = obj.sayHello();
        System.out.println(message);
    }
}

if I run the server using:
java -Djavax.net.ssl.keyStore=keystore - Djavax.net.ssl.keyStorePassword=password server/RmiServer

and the client
java -Djavax.net.ssl.trustStore=truststore -Djavax.net.ssl.trustStorePassword=trustword HelloClient

everything …

Ummmm I tried implementing SSL on the big project now but .. omg the errors I get ....

This is how it is implemented on the server side

        super(0, new SslRMIClientSocketFactory(), new SslRMIServerSocketFactory());
                                System.setProperty("javafx.net.ssl.keyStore","C:\\Users\\Slavi\\workspace\\PrintServer\\src\\server\\keystore.jks");
        System.setProperty("javafx.net.ssl.keyStorePassword","password");

and this is the Client side

System.setProperty("javafx.net.ssl.truststore","C:\\Users\\Slavi\\workspace\\PrintServer\\src\\application\\truststore.jks");
        System.setProperty("javafx.net.ssl.trustStorePassword","trustword");

when the client tries to communicate, these are the errors I get ...

connection established localhost:3232
Exception in thread "JavaFX Application Thread" java.lang.RuntimeException: java.lang.reflect.InvocationTargetException
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1768)
    at javafx.fxml.FXMLLoader$ControllerMethodEventHandler.handle(FXMLLoader.java:1651)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:86)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:49)
    at javafx.event.Event.fireEvent(Event.java:204)
    at javafx.scene.Node.fireEvent(Node.java:8175)
    at javafx.scene.control.Button.fire(Button.java:185)
    at com.sun.javafx.scene.control.behavior.ButtonBehavior.mouseReleased(ButtonBehavior.java:182)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:96)
    at com.sun.javafx.scene.control.skin.BehaviorSkinBase$1.handle(BehaviorSkinBase.java:89)
    at com.sun.javafx.event.CompositeEventHandler$NormalEventHandlerRecord.handleBubblingEvent(CompositeEventHandler.java:218)
    at com.sun.javafx.event.CompositeEventHandler.dispatchBubblingEvent(CompositeEventHandler.java:80)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:238)
    at com.sun.javafx.event.EventHandlerManager.dispatchBubblingEvent(EventHandlerManager.java:191)
    at com.sun.javafx.event.CompositeEventDispatcher.dispatchBubblingEvent(CompositeEventDispatcher.java:59)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:58)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:56)
    at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:114)
    at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:74)
    at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:54)
    at javafx.event.Event.fireEvent(Event.java:204)
    at javafx.scene.Scene$MouseHandler.process(Scene.java:3746)
    at javafx.scene.Scene$MouseHandler.access$1800(Scene.java:3471)
    at javafx.scene.Scene.impl_processMouseEvent(Scene.java:1695)
    at javafx.scene.Scene$ScenePeerListener.mouseEvent(Scene.java:2486)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:314)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler$MouseEventNotification.run(GlassViewEventHandler.java:243)
    at java.security.AccessController.doPrivileged(Native Method)
    at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleMouseEvent(GlassViewEventHandler.java:345)
    at com.sun.glass.ui.View.handleMouseEvent(View.java:526)
    at com.sun.glass.ui.View.notifyMouse(View.java:898)
    at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at com.sun.glass.ui.win.WinApplication.access$300(WinApplication.java:39)
    at com.sun.glass.ui.win.WinApplication$4$1.run(WinApplication.java:112)
    at java.lang.Thread.run(Thread.java:745)
Caused by: java.lang.reflect.InvocationTargetException
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at sun.reflect.misc.Trampoline.invoke(MethodUtil.java:71)
    at sun.reflect.GeneratedMethodAccessor1.invoke(Unknown Source)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:483)
    at sun.reflect.misc.MethodUtil.invoke(MethodUtil.java:275)
    at javafx.fxml.FXMLLoader$MethodHandler.invoke(FXMLLoader.java:1765)
    ... 47 more
Caused by: java.rmi.ConnectIOException: error during JRMP connection establishment; nested exception is: 
    javax.net.ssl.SSLHandshakeException: Received fatal alert: handshake_failure
    at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:304)
    at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202)
    at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:130)
    at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194)
    at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148)
    at com.sun.proxy.$Proxy2.validateCredentials(Unknown Source)
    at application.ClientViewController.handleLogIn(ClientViewController.java:159)
    ... 57 more
Caused by: javax.net.ssl.SSLHandshakeException: Received fatal alert: handshake_failure
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
    at sun.security.ssl.Alerts.getSSLException(Alerts.java:154)
    at sun.security.ssl.SSLSocketImpl.recvAlert(SSLSocketImpl.java:1991)
    at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1104)
    at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1343) …

It is what it demands, the project is aimed at security :P

Hey everyone,
I;ve implemented SSL to my server using this guide

now when I connect the server it takes some time to initialize now, I assume its setting up stuff, and then when the client connects takes awhile as well (few seconds), I'd assume it works but I want to see a log or something where client and server create the handshake, any ideas how? The way that I start my server is:

java -Djavax.net.ssl.keyStore=keystore -Djavax.net.ssl.keyStorePassword=password HelloImpl &

What I tried was to use:

System.setProperty("javafx.net.ssl.keyStore","C:\\Users\\Slavi\\workspace\\rmiSSL\\keystore");
System.setProperty("javafx.net.ssl.keyStorePassword","password");

and then start the server using
-Djavax.net.ssl.debug=all -cp . HelloImpl > 1.txt HelloImpl &
by doing so it prints out a lot of information in a file but at the end I don't see the things that my server is supposed to return when its up and running such as "Server running"

then I commented out the setProperty lines and tried started the server using
java -Djavax.net.ssl.keyStore=keystore -Djavax.net.ssl.keyStorePassword=password -Djavax.net.ssl.debug=all -cp . HelloImpl > 1.txt HelloImpl &
and then in my text file I only get "Server running" and no information about the handshake after a client connets or what so ever. Although when I run a client, everything seems pretty smooth, and I get the expected result on client side

Any ideas? :x

from what I understand, when you click b2 for example, you want ur op1 to be 2? If so, in actionPerformed, the if statements .. for example

if source was b2
    if op1 is empty , op1 = 2;
    else op2 = 2;

and so on until you fill it for all of them.
At the end when all if else statements are checked, you can do operations the input or just write the answers out to the third text field

First of all, you are missing class declearation in your file!!!!

try using for loop to print out the values of the LinkedList? Also, why do u need the linkedlist if its just a number keep it only as int n then you could
System.out.println("The user entered number of employees: " +n);

Hey guys,
Yeah I wouldn't try to write my own crypto functions. The link that James linked earlier contains a full implementation of PBKDF2, which is another key scretching algorithm, just like bcrypt. I was thinking I would use that? Looked at the code seems pretty decent. Or, should I go for bcrypt?

Also @sos,
implementing secure connection was one of the advanced stuff that is part of the project, which I am definitely going for as I want to get highest grades only, and I was thinking I'd try to implement SSL after the password is sorted, would that be okay?

Oh great, yeah I remember reading that article 1-2 years ago, will relook it, Thank you James and everyone!

Oh, yea that sounds pretty nice actually.
By the way James, could you suggest anything on the authentication problem as well?

Hey guys,
thank you for answering

Yeah, I found it weird as well that's why i wanted to input from you :), I don't understand what is the logic behind client being able to do that. I am considering to just skip those methods and maybe ask the teacher what exactly he means by that and I guess it will be as you guys proposed, having a second server ...

Also maybe you could give me some ideas on my next thing ...

When clients connect to the print server, they need to be authenticated as well or they won't be able to print otherwise. My idea is to have a method that returns a boolean but I need to consider how to store the passwords on the server side. I could use a database, file with hashed passwords etc ..
I am thinking of having a file with hashed passwords but I don't want to have the passwords just MD5'd for example. It's been proven to be broken so I want a bit more secure system. I was thinking about salting the password but I have no clue at the moment how to store the salt, would it be in different file maybe and assign it to the username?

Also, are there any cryptographic hashes that are already defined and we could just use?

Hey guys,
Just got a quick question ... I am implementing a client GUI, and part of the requirements are that the client is able to start, stop and restart the server. This got me a bit confused since the client connects after the server is running. What I am thinking now is do the mean disconect the client himself if he presses Stop? and make new one if he presses start after? Here is the definition I've got given

start(); // starts the print server
stop(); // stops the print server
restart(); // stops the print server, clears the print queue and starts the print server again

If it actually interacts with the server itself, how would that happen? :o For my communication I am using Java RMI

Nevermind, dumb moment only had to restart the server as the method didn't exist before i started it :p

Hello everyone,
I am getting NPE, and surprisingly I can't figure out why ... I am calling a method from a client using java rmi. The method on the server side is as follows :

public List<String> getPrinters() throws RemoteException {
        List<String> listPrinters= new ArrayList<String>();
        for(int i=0; i<printers.size();i++){
            listPrinters.add(printers.get(i).getName());
        }
        return listPrinters;
    }

and then from the client side I am trying to
System.out.println(rmiServer.getPrinters().size());

The connection is successful etc because i am sending some strings and replying back after so its all fine, gives me NPE on the client side while trying to print the size of the list that the method should return

Ideas? =)

Thank you james, I'll see what I can do .. but definitely not happy on my choices ;)

Hello James,
so I'd have to implement the entire thing in java rmi? :s

Hey everyone,
I am facing an implementaton issue here ... hopefully someone can give me a hand ..

So I am implementing a client-server communication, where the server has to act as a print server. In other words, the client simulates to be next to a printer and can send a file to be printed, can check whats on the queue to be printed, can prioritize the queue etc ...

So far, I have a class Client and a class Server. The client can connect to the server using sockets, says "hi", receives the message back and disconnects ..

I also have a class Printer, which has few fields and methods such as String name, and getters/setters, it has a queue etc, nothing out of ordinary.

Now I started designing the GUI for the client and it is pretty much done, has buttons and text area where information will be displayed such as printer status, whats on queue etc.

Initially when the server is made, it creates a list of printers, from which the user can select which to use ...
Now, the problem that I am facing is I want to ask for the list from the client GUI, but I am confused(haven't slept in very long time so this must be a factor! :D) how can I actually do that? Like, I can click the button on the gui, but I have no idea what the server should expect to receive in order to return back …

public class MyProgram{
    //Enter your code or be more specific when asking a question!
}

Can you point out what is wrong in the output?

was missing "\n" when sending the "Hello"

What do you need help with exactly? Noone would just write the entire thing for you ...

Hey guys,
I can't understand why am I not getting anything from the server, it is supposed to return "Hello" to the client ... I have this code implemented for a game I made during the summer and it works perfectly(of course this is just part of the code), but just started a new project and got stucked on it already and I can't find a reasonable explanation for it .. Here's the code ..

Server

package server;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.ServerSocket;
import java.net.Socket;
import java.util.ArrayList;






public class AuthServer extends Thread{
    private ServerSocket serverSocket;
    private ArrayList<ClientThread> alThreads = new ArrayList<ClientThread>();
    String input1;

    public AuthServer(int port)throws IOException{
        serverSocket = new ServerSocket(port);
    }

    public static void main(String[] args){
        int port = 9001;
        try{
            Thread t = new AuthServer(port);
            t.start();
        }catch(IOException e){
            e.printStackTrace();
        }
    }


    public void run(){
        while(true){
            try{
                System.out.println("Starting to run");
                Socket server = serverSocket.accept();
                ClientThread ct = new ClientThread(server);
                alThreads.add(ct);
                ct.start();

            } catch(IOException e){
                e.printStackTrace();
            }
        }
    }
    public class ClientThread extends Thread{
        Socket clientSocket;
        PrintWriter out;

        public ClientThread(Socket s){
            this.clientSocket = s;
        }
        public void run(){

            try{
                out = new PrintWriter(clientSocket.getOutputStream(), true);
                BufferedReader in = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
                System.out.println("waiting");
                String input = in.readLine();
                System.out.println(input);
                input1 = in.readLine();
                for(ClientThread t:alThreads){
                    t.print();
                }


            } catch(IOException e){
                e.printStackTrace();
            } 
        }
        public void print() throws IOException{
            this.out.print(input1+ "\n");
            this.out.flush();

        }
    }
}

Client

package client;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.PrintWriter;
import java.net.Socket;

public class Client {
    String defaultHost;
    int defaultPort; …

Means the symbol is not found, not decleared or doesn't exist in the language syntax

What error do you get?

Hey lena,
There was a daniweb member trying to create voIP using java, as far as I know he didn't manage to finish that project, it seems to be difficult in a way, but if you start and show us some work I am pretty sure we'll figure out something but for start I'd like to point you to look here :)

I'd also include that for my own preferences I'd go for what @herices said but with more brackets for clear reading
else if((code != 1) && (code != 2) && (code != 3) && (code != 4))

Next thing, you should probably check whether the number is between 1-4 first before executing the if statements, in other words you can start with an if statement such as
if((code != 1) && (code != 2) && (code != 3) && (code != 4))
then print error,
else()
include all your code in here for the rest

Next you are not using the numbers you get from the user? Do you mean by your 1 and 2 to have the user number 1 and user number 2? If so, fix it ... Also, this is what @Stultuske meant

You have to burn it as an image not just a single copy paste, in other words using a dvd burning program, another solution is to make a bootable flash drive, using Universal USB installer is most likely the best solution to make linux on bootable flash

Isn't it being printed just as a static string value in the print method?
perhaps if you show some code ..

Try reinstalling java jre, I think the latest version up to date is 8u25

By coding?

Hey Sepp!, thanks for replying!
I see, I'll try to fix it a bit :)

Do you understand the default constructor that was implemented, why it was needed and what it does?

The error of totalvalue is because you are inheriting from Cars where it has already been implemented and now you are trying to return a different data type.

Get prod number returns an error because u haven't closed your constructor

Without looking into your code quickly I'd think that the first error is because you haven't closed something defined before the beggining of the method and the second one is you are returning an int value while expecting a float

Hey guys, i am facing a small problem here, perhaps you could give me any hints with it.

In one of my courses (Program analysis) we are using a language called "The While language" , it is simplified and I think only for education purposes. I am asked to make an abstract syntax out of the concrete one, during it in a language of my choice. This abstract syntax will be used later on to generate the language parser(I think?), Anyway here is the concrete syntax of the language

a   ::= n | x | A[a] | a1  opa a2 | -a | (a)
b   ::= true | false | a1 opr a2 | b1 opb b2 | !b | (b)
S   ::= x := a; | skip; | A[a1] := a2; | read x; | read A[a]; | write a; | 
S1  S2 | if b then  S1 else S2 fi; | while b do S od;
D   ::= int x; | int A[n]; | ∊ | D1 D2
P   ::=     program D S end



opa ∈   {+, -, *, /}        int × int → int
opr ∈   {<, >, <=, >=, =, !=} int × int → bool
opb ∈   {&, |}          bool × bool → bool

Soo, so far so good, I started creating the abstract syntax but I got stucked in a way after talking to the TA. Here is what I have right now

public abstract class Exp {}
public abstract class …

Are you getting any errors on the last code now? If so which if not, what questions do you have about it?

Seems like an assignment, what have you done so far? Here's some tips

While loop will keep the program running until user terminates it
cin operator takes an input from the user, such as 500, I assume your input is in grams? multiple it with 1000 and the result will be in kilograms.
cout operator can be used to print back to the user how much was the entered value in kilograms.
At this point you can ask the user whether he wants to continue or exit, using if/else statement will do it such as if user inputs 'q' , terminate the program else, start the loop over

If you face any issues post back with your current code and what exactly you need help with, as no one in here is willing to do it(your homework) for you

I see, well I'll get busy and implement it I guess, thank you!

Hey there sepp2k,
Thank you for your response!
I am pretty happy that you wrote that example, because I am sure that other members will find it useful as well, but I was just wondering what exactly my question was. I wrote an email to my lecturer but no response back still ;(
Do you think the question means that I have to explain what ABS in general is?:o

Havent done android inawhile but you created 2 buttons with 2 different id's , and if you don't link a handler to the first one, nothing will happen whenever it is clicked

deaf

Exactly what Jim said, if you want to keep something private, don't put it on the net ;)

Hey guys, just heads up to change your passwords!, here is the story on the hacker news Link

meal (eating atm :D)

As James said, you can set them in the default contructor on line 7, and just set your variable to some strings of your choice, so whenever you create a person he will be automatically assigned to those strings, which could represent names etc

Hey guys,
I am facing a problem with one of my homeworks, it states:

The various analyses implemented in the program analysis module will
make use of a number of general data structures and algorithms and in
this exercise we shall focus on those.

The parser provides a representation of the abstract syntax tree;
specify this data structure in your implementation language

I have no idea what are they asking me to do, perhaps one of you had any experience with this and can help me out
Well, is it to explain what AST is or how is it implemented in Java? or idk =D

Interesting ..

Well, I bought it ;) I think I should also receive an invite now in the future :)

I think you have to loop through the list to print out each element instead of just a simple System.out.println(), try using iterator or for loop also works until next element is null (as its the last data in the list)

Take a look at Click Here

Hey guys .. I just got an invite to buy oneplus one, and it expires in 24 hours. I have samsung galaxy s3 currently, any suggestions should I go for it, whats its performance?

Thanks 4 sharing