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• Bouncy Castle, RSA : transforming keys into a String format

  - by Rami W.

  Hi, iam using RSA(Bouncy Castle API) in my c# porject. Igenerated the keypair with this method RsaKeyPairGenerator r = new RsaKeyPairGenerator(); r.Init(new KeyGenerationParameters(new SecureRandom(), 1024)); AsymmetricCipherKeyPair keys = r.GenerateKeyPair(); AsymmetricKeyParameter private_key = keys.Private; AsymmetricKeyParameter public_key = keys.Public; now i want to save them in txt file but the problem is that i can't convert them to a string format. i read in another post that keys must be serialized using PrivateKeyInfo k = PrivateKeyInfoFactory.CreatePrivateKeyInfo(private_key); byte[] serializedKey = k.ToAsn1Object().GetDerEncoded(); Is it the right way ? if yes, what should i do after this ? just convert them from byte[] to String ? thx for any help.

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• How do you implement position-sensitive zooming inside a JScrollPane?

  - by tucuxi

  I am trying to implement position-sensitive zooming inside a JScrollPane. The JScrollPane contains a component with a customized 'paint' that will draw itself inside whatever space it is allocated - so zooming is as easy as using a MouseWheelListener that resizes the inner component as required. But I also want zooming into (or out of) a point to keep that point as central as possible within the resulting zoomed-in (or -out) view (this is what I refer to as 'position-sensitive' zooming), similar to how zooming works in google maps. I am sure this has been done many times before - does anybody know the "right" way to do it under Java Swing?. Would it be better to play with Graphic2D's transformations instead of using JScrollPanes? Sample code follows: package test; import java.awt.*; import java.awt.event.*; import java.awt.geom.*; import javax.swing.*; public class FPanel extends javax.swing.JPanel { private Dimension preferredSize = new Dimension(400, 400); private Rectangle2D[] rects = new Rectangle2D[50]; public static void main(String[] args) { JFrame jf = new JFrame("test"); jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); jf.setSize(400, 400); jf.add(new JScrollPane(new FPanel())); jf.setVisible(true); } public FPanel() { // generate rectangles with pseudo-random coords for (int i=0; i<rects.length; i++) { rects[i] = new Rectangle2D.Double( Math.random()*.8, Math.random()*.8, Math.random()*.2, Math.random()*.2); } // mouse listener to detect scrollwheel events addMouseWheelListener(new MouseWheelListener() { public void mouseWheelMoved(MouseWheelEvent e) { updatePreferredSize(e.getWheelRotation(), e.getPoint()); } }); } private void updatePreferredSize(int n, Point p) { double d = (double) n * 1.08; d = (n > 0) ? 1 / d : -d; int w = (int) (getWidth() * d); int h = (int) (getHeight() * d); preferredSize.setSize(w, h); getParent().doLayout(); // Question: how do I keep 'p' centered in the resulting view? } public Dimension getPreferredSize() { return preferredSize; } private Rectangle2D r = new Rectangle2D.Float(); public void paint(Graphics g) { super.paint(g); g.setColor(Color.red); int w = getWidth(); int h = getHeight(); for (Rectangle2D rect : rects) { r.setRect(rect.getX() * w, rect.getY() * h, rect.getWidth() * w, rect.getHeight() * h); ((Graphics2D)g).draw(r); } } }

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• Help with complex sql query

  - by eugeneK

  To make story short, i'm building self-learning banner management system. Users will be able to insert these banners to their site when banners will be shown based on sales/impressions ratio. I have 4 tables Banners bannerID int bannerImage varchar.... SmartBanners smartBannerID int smartBannerArrayID int bannerID int impressionsCount int visibility tinyint (percents) SmartBannerArrays smartBannerArrayID int userID int Statistics bannerID int saleAmountPerDay decimal... Each night i need to generate new "visibility" for each SmartBanner based on whole SmartBannerArray that same user has. So i need to get sum of impressions and sales for each bannerID in SmartBannerArray. All comes to my mind is to use double cursor, one will loop thought SmartBannerArrays get needed values for sum of impressions and sales and then inner loop which will access each SmartBanner and change it's "visibility" percentage based on (sales/impressions)/(sumOfSales/sumOfImpressions)*100 Hope you get the picture... Is there any other way to design better tables or not to use double cursor to avoid server overload ?

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• Argument passing regarding ivars

  - by StoneBreaker

  I am passing an iVar into a function. The iVar is a double. The value of the iVar inside the function is correct, but the value of the iVar outside the function is not changed. This must have something to do with the way that I am receiving the iVar into the function. How do I pass a double iVar in so that its value is changed in the object and not only in the function? I do the same thing with pointers and the results are as expected, so I think I am not understanding scalar argument passing in c/objective-c.

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• Declarative JDOQL vs Single-String JDOQL : performance

  - by DrDro

  When querying with JDOQL is there a performance difference between using the declarative version and the Single-String version: Example from the JDOQL doc: //Declarative JDOQL : Query q = pm.newQuery(org.jpox.Person.class, "lastName == \"Jones\" && age < age_limit"); q.declareParameters("double age_limit"); List results = (List)q.execute(20.0); //Single-String JDOQL : Query q = pm.newQuery("SELECT FROM org.jpox.Person WHERE lastName == \"Jones\"" + " && age < :age_limit PARAMETERS double age_limit"); List results = (List)q.execute(20.0); Other then performance, are there any reasons for which one is better to use then the other or is it just about the one with which we feel more comfortable.

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• Detecting incorrect key using AES/GCM in JAVA

  - by 4r1y4n

  I'm using AES to encrypt/decrypt some files in GCM mode using BouncyCastle. While I'm proving wrong key for decryption there is no exception. How should I check that the key is incorrect? my code is this: SecretKeySpec incorrectKey = new SecretKeySpec(keyBytes, "AES"); IvParameterSpec ivSpec = new IvParameterSpec(ivBytes); Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding", "BC"); byte[] block = new byte[1048576]; int i; cipher.init(Cipher.DECRYPT_MODE, incorrectKey, ivSpec); BufferedInputStream fis=new BufferedInputStream(new ProgressMonitorInputStream(null,"Decrypting ...",new FileInputStream("file.enc"))); BufferedOutputStream ro=new BufferedOutputStream(new FileOutputStream("file_org")); CipherOutputStream dcOut = new CipherOutputStream(ro, cipher); while ((i = fis.read(block)) != -1) { dcOut.write(block, 0, i); } dcOut.close(); fis.close(); thanks

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• How to best integrate generated code

  - by Arne

  I am evaluating the use of code generation for my flight simulation project. More specifically there is a requirement to allow "the average engineer" (no offense I am one myself) to define the differential equations that describe the dynamic system in a more natural syntax than C++ provides. The idea is to devise a abstract descriptor language that can be easily understood and edited to generate C++ code from. This descriptor is supplied by the modeling engineer and used by the ones implementing and maintaining the simulation evironment to generate code. I've got something like this in mind: model Aircraft has state x1, x2; state x3; input double : u; input bool : flag1, flag2; algebraic double : x1x2; model Engine : tw1, tw2; model Gear : gear; model ISA : isa; trim routine HorizontalFight; trim routine OnGround, General; constant double : c1, c2; constant int : ci1; begin differential equations x1' = x1 + 2.*x2; x2' = x2 + x1x2; begin algebraic equations x1x2 = x1*x2 + x1'; end model It is important to retain the flexibility of the C language thus the descriptor language is meant to only define certain parts of the definition and implementation of the model class. This way one enigneer provides the model in from of the descriptor language as examplified above and the maintenance enigneer will add all the code to read parameters from files, start/stop/pause the execution of the simulation and how a concrete object gets instatiated. My first though is to either generate two files from the descriptor file: one .h file containing declarations and one .cpp file containing the implementation of certain functions. These then need to be #included at appropriate places [File Aircarft.h] class Aircraft { public: void Aircraft(..); // hand-written constructor void ReadParameters(string &file_name); // hand-written private: /* more hand wirtten boiler-plate code */ /* generate declarations follow */ #include "Aircraft.generated.decl" }; [File Aircraft.cpp] Aircarft::Aircraft(..) { /* hand-written constructer implementation */ } /* more hand-written implementation code */ /* generated implementation code follows */ #include "Aircraft.generated.impl" Any thoughts or suggestions?

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• when i try to save this file it creates and folder for the entire path

  - by girish

  ZipFileToCreate = "c:\user\desktop\webservice\file.zip"; so, when i try to save this file it creates the folder for the path like user\desktop\webservice\file\ why is it so, FileStream fs = new FileStream(ZipFileToCreate, FileMode.Open); byte[] data = new Byte[fs.Length]; BinaryReader br = new BinaryReader(fs); br.Read(data, 0, data.Length); br.Close(); Response.Clear(); Response.ContentType = "application/x-zip-compressed"; Response.AppendHeader("Content-Disposition", "filename=" + Parameter + ".zip"); DeleteOldFiles(); Response.BinaryWrite(data);

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• Memory in Eclipse

  - by user247866

  I'm getting the java.lang.OutOfMemoryError exception in Eclipse. I know that Eclipse by default uses heap size of 256M. I'm trying to increase it but nothing happens. For example: eclipse -vmargs -Xmx16g -XX:PermSize=2g -XX:MaxPermSize=2g I also tried different settings, using only the -Xmx option, using different cases of g, G, m, M, different memory sizes, but nothing helps. Does not matter which params I specify, the heap exception is thrown at the same time, so I assume there's something I'm doing wrong that Eclipse ignores the -Xmx parameter. I'm using a 32GB RAM machine and trying to execute something very simple such as: double[][] a = new double[15000][15000]; It only works when I reduce the array size to something around 10000 on 10000. I'm working on Linux and using the top command I can see how much memory the Java process is consuming; it's less than 2%. Thanks!

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• question about VHDL coding tips and tricks

  - by davit-datuashvili

  please explain me how this algorithm works ? http://vhdlguru.blogspot.com/2010/04/8-bit-binary-to-bcd-converter-double.html

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• bin_at in dlmalloc

  - by chunhui

  In glibc malloc.c or dlmalloc It said "repositioning tricks"As in blew, and use this trick in bin_at. bins is a array,the space is allocated when av(struct malloc_state) is allocated.doesn't it? the sizeof(bin[i]) is less then sizeof(struct malloc_chunk*)? Who can describe this trick for me? I can't understand the bin_at macro.why they get the bins address use this method?how it works? Very thanks,and sorry for my poor English. /* To simplify use in double-linked lists, each bin header acts as a malloc_chunk. This avoids special-casing for headers. But to conserve space and improve locality, we allocate only the fd/bk pointers of bins, and then use repositioning tricks to treat these as the fields of a malloc_chunk*. */ typedef struct malloc_chunk* mbinptr; /* addressing -- note that bin_at(0) does not exist */ #define bin_at(m, i) \ (mbinptr) (((char *) &((m)->bins[((i) - 1) * 2])) \ - offsetof (struct malloc_chunk, fd)) The malloc_chunk struct like this: struct malloc_chunk { INTERNAL_SIZE_T prev_size; /* Size of previous chunk (if free). */ INTERNAL_SIZE_T size; /* Size in bytes, including overhead. */ struct malloc_chunk* fd; /* double links -- used only if free. */ struct malloc_chunk* bk; /* Only used for large blocks: pointer to next larger size. */ struct malloc_chunk* fd_nextsize; /* double links -- used only if free. */ struct malloc_chunk* bk_nextsize; }; And the bin type like this: typedef struct malloc_chunk* mbinptr; struct malloc_state { /* Serialize access. */ mutex_t mutex; /* Flags (formerly in max_fast). */ int flags; #if THREAD_STATS /* Statistics for locking. Only used if THREAD_STATS is defined. */ long stat_lock_direct, stat_lock_loop, stat_lock_wait; #endif /* Fastbins */ mfastbinptr fastbinsY[NFASTBINS]; /* Base of the topmost chunk -- not otherwise kept in a bin */ mchunkptr top; /* The remainder from the most recent split of a small request */ mchunkptr last_remainder; /* Normal bins packed as described above */ mchunkptr bins[NBINS * 2 - 2]; /* Bitmap of bins */ unsigned int binmap[BINMAPSIZE]; /* Linked list */ struct malloc_state *next; #ifdef PER_THREAD /* Linked list for free arenas. */ struct malloc_state *next_free; #endif /* Memory allocated from the system in this arena. */ INTERNAL_SIZE_T system_mem; INTERNAL_SIZE_T max_system_mem; };

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• quantity of measurable units design pattern

  - by Berryl

  Hello I am thinking through a nice pattern to be useful across domains of measurable units (ie, Length, Time) and came up with the following use case and initial classes, and of course, questions! 1) Does a Composite pattern help or complicate? 2) Should the Convert method(s) in the ComposityNode be a separate converter class? All comments appreciated. Cheers, Berryl Example Use Case: var inch = new ConvertableUnit("inch", 1) var foot = new ConvertableUnit("foot", 12) var imperialUnits = new CompositeConvertableUnit("imperial units", .024) imperialUnits.AddChild(inch) imperialUnits.AddChild(foot) var meter = new ConvertableUnit("meter", 1) var millimeter = new ConvertableUnit("millimeter ", .001) var imperialUnits = new CompositeConvertableUnit("metric units", 1) imperialUnits.AddChild(meter) imperialUnits.AddChild(millimeter) var oneInch = new Quantity(1, inch); var oneFoot = new Quantity(1, foot); oneFoot.ToBase() // "12 inches" var oneMeter = new Quantity(1, meter); oneInch.ToBase() // .024 meters Possible Solution ConvertableUnit : Node double Rate string Name Quantity ConvertableUnit Unit double Amount CompositeConvertableUnit : Node ISet<ConvertableUnit> _children ConvertableUnit BaseUnit {get{ return _children.Where(c=>c.Rate == 1).First() } } Quantity ConvertTo(Quantity from, Quantity to) Quantity ToBase(Quantity from);

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• How to read a password encrypted key with java?

  - by Denis

  Hi, This is very simple question. I have private key stored in file in PKCS8 DER format and protected by password. What is the easiest way to read it? Here is the code I use to load unencrypted one: InputStream in = new FileInputStream(privateKeyFilename); byte[] privateKeydata = new byte[in.available()]; in.read(privateKeydata); in.close(); KeyFactory privateKeyFactory = KeyFactory.getInstance("RSA"); PKCS8EncodedKeySpec encodedKeySpec = new PKCS8EncodedKeySpec(privateKeydata); PrivateKey privateKey = privateKeyFactory.generatePrivate(encodedKeySpec); Please, Help!!!

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• Correct way to Convert 16bit PCM Wave data to float

  - by fredley

  I have a wave file in 16bit PCM form. I've got the raw data in a byte[] and a method for extracting samples, and I need them in float format, i.e. a float[] to do a Fourier Transform. Here's my code, does this look right? I'm working on Android so javax.sound.sampled etc. is not available. private static short getSample(byte[] buffer, int position) { return (short) (((buffer[position + 1] & 0xff) << 8) | (buffer[position] & 0xff)); } ... float[] samples = new float[samplesLength]; for (int i = 0;i<input.length/2;i+=2){ samples[i/2] = (float)getSample(input,i) / (float)Short.MAX_VALUE; }

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• How can I make an "abstract" enum in a .NET class library?

  - by Lazlo

  I'm making a server library in which the packet association is done by enum. public enum ServerOperationCode : byte { LoginResponse = 0x00, SelectionResponse = 0x01, BlahBlahResponse = 0x02 } public enum ClientOperationCode : byte { LoginRequest = 0x00, SelectionRequest = 0x01, BlahBlahRequest = 0x02 } That works fine when you're working in your own project - you can compare which enum member is returned (i.e. if (packet.OperationCode == ClientOperationCode.LoginRequest)). However, since this is a class library, the user will have to define its own enum. Therefore, I have two enums to add as "abstract" - ServerOperationCode and ClientOperationCode. I know it's not possible to implement abstract enums in C#. How would I go doing this?

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• How do I recieve byteArray send from Server and read 4 single bytes at a time.

  - by k80sg

  I need to receive 320 bytes of data from a server which consist of 80 4 bytes int fields. How do I receive them in bytes of 4 and display their respective int values? Thanks. Not sure if this is right for the receiving part: //for reading the data from the socket BufferedInputStream bufferinput=new BufferedInputStream(NewSocket.getInputStream()); DataInputStream datainput=new DataInputStream(bufferinput); byte[] handsize=new byte[32]; // The control will halt at the below statement till all the 32 bytes are not read from the socket. datainput.readFully(handsize);

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• Java multiple connections downloading file

  - by weulerjunior

  Hello friends, I was wanting to add multiple connections in the code below to be able to download files faster. Could someone help me? Thanks in advance. public void run() { RandomAccessFile file = null; InputStream stream = null; try { // Open connection to URL. HttpURLConnection connection = (HttpURLConnection) url.openConnection(); // Specify what portion of file to download. connection.setRequestProperty("Range", "bytes=" + downloaded + "-"); // Connect to server. connection.connect(); // Make sure response code is in the 200 range. if (connection.getResponseCode() / 100 != 2) { error(); } // Check for valid content length. int contentLength = connection.getContentLength(); if (contentLength < 1) { error(); } /* Set the size for this download if it hasn't been already set. */ if (size == -1) { size = contentLength; stateChanged(); } // Open file and seek to the end of it. file = new RandomAccessFile("C:\\"+getFileName(url), "rw"); file.seek(downloaded); stream = connection.getInputStream(); while (status == DOWNLOADING) { /* Size buffer according to how much of the file is left to download. */ byte buffer[]; if (size - downloaded > MAX_BUFFER_SIZE) { buffer = new byte[MAX_BUFFER_SIZE]; } else { buffer = new byte[size - downloaded]; } // Read from server into buffer. int read = stream.read(buffer); if (read == -1) { break; } // Write buffer to file. file.write(buffer, 0, read); downloaded += read; stateChanged(); } /* Change status to complete if this point was reached because downloading has finished. */ if (status == DOWNLOADING) { status = COMPLETE; stateChanged(); } } catch (Exception e) { error(); } finally { // Close file. if (file != null) { try { file.close(); } catch (Exception e) { } } // Close connection to server. if (stream != null) { try { stream.close(); } catch (Exception e) { } } } }

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• Java Regex for matching quoted string with escaped quotes

  - by kayahr

  I know there are already many questions like mine but I found no answer which works in Java. So I write a new question. I have text files with content like this: key1 = "This is a \"test\" text with escapes using '\\' characters"; key2 = 'It must work with \'single\' quotes and "double" quotes'; I need a regular expression which matches the values in the double-quotes (or single-quotes). This regular expression must support the escaped quotes and escaped backslashes. The regular expression must work with Java standard Pattern/Matcher classes.

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• How can I parse a C header file with Perl?

  - by Alphaneo

  Hi, I have a header file in which there is a large struct. I need to read this structure using some program and make some operations on each member of the structure and write them back. For example I have some structure like const BYTE Some_Idx[] = { 4,7,10,15,17,19,24,29, 31,32,35,45,49,51,52,54, 55,58,60,64,65,66,67,69, 70,72,76,77,81,82,83,85, 88,93,94,95,97,99,102,103, 105,106,113,115,122,124,125,126, 129,131,137,139,140,149,151,152, 153,155,158,159,160,163,165,169, 174,175,181,182,183,189,190,193, 197,201,204,206,208,210,211,212, 213,214,215,217,218,219,220,223, 225,228,230,234,236,237,240,241, 242,247,249}; Now, I need to read this and apply some operation on each of the member variable and create a new structure with different order, something like: const BYTE Some_Idx_Mod_mul_2[] = { 8,14,20, ... ... 484,494,498}; Is there any Perl library already available for this? If not Perl, something else like Python is also OK. Can somebody please help!!!

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• Interop: HmacSHA1 in Java and dotNet

  - by wilth

  Hello, In an app we are calculating a SHA1Hmac in java using the following: SecretKey key = new SecretKeySpec(secret, "HmacSHA1"); Mac m = Mac.getInstance("HmacSHA1"); m.init(secret); byte[] hmac = m.doFinal(data); And later, the hmac is verified in C# - on a SmartCard - using: HMACSHA1 hmacSha = new HMACSHA1(secret); hmacSha.Initialize(); byte[] hmac = hmacSha.ComputeHash(data); However, the result is not the same. Did I overlook something important? The inputs seem to be the same. Here some sample inputs: Data: 546573746461746131323341fa3c35 Key: 6d795472616e73616374696f6e536563726574 Result Java: 37dbde318b5e88acbd846775e38b08fe4d15dac6 Result C#: dd626b0be6ae78b09352a0e39f4d0e30bb3f8eb9 I wouldn't mind to implement my own hmacsha1 on both platforms, but using what already exists.... Thanks!

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• Async Socket Listener on separate thread - VB.net

  - by TheHockeyGeek

  I am trying to use the code from Microsoft for an Async Socket connection. It appears the listener runs in the main thread locking the GUI. I am new at both socket connections and multi-threading all at the same time. Having a hard time getting my mind wrapped around this all at once. The code used is at http://msdn.microsoft.com/en-us/library/fx6588te.aspx Using this example, how can I move the listener to its own thread? Public Shared Sub Main() ' Data buffer for incoming data. Dim bytes() As Byte = New [Byte](1023) {} ' Establish the local endpoint for the socket. Dim ipHostInfo As IPHostEntry = Dns.GetHostEntry(Dns.GetHostName()) Dim ipAddress As IPAddress = ipHostInfo.AddressList(1) Dim localEndPoint As New IPEndPoint(ipAddress, 11000) ' Create a TCP/IP socket. Dim listener As New Socket(AddressFamily.InterNetwork, SocketType.Stream, ProtocolType.Tcp) ' Bind the socket to the local endpoint and listen for incoming connections. listener.Bind(localEndPoint) listener.Listen(100)

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• Is there any reason to throw a DivideByZeroException?

  - by Atomiton

  Are there any cases when it's a good idea to throw errors that can be avoided? I'm thinking specifically of the DivideByZeroException and NullReferenceException For example: double numerator = 10; double denominator = getDenominatorFromUser(); if( denominator == 0 ){ throw new DivideByZeroException("You can't divide by Zero!"); } Are there any reasons for throwing an error like this? NOTE: I'm not talking about catching these errors, but specifically in knowing if there are ever good reasons for throwing them.

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• How to generate GIR files from the Vala compiler?

  - by celil

  I am trying to create python bindings to a vala library using pygi with gobject introspection. However, I am having trouble generating the GIR files (that I am planning to compile to typelib files subsequently). According to the documentation valac should support generating GIR files. Compiling the following helloworld.vala public struct Point { public double x; public double y; } public class Person { public int age = 32; public Person(int age) { this.age = age; } } public int main() { var p = Point() { x=0.0, y=0.1 }; stdout.printf("%f %f\n", p.x, p.y); var per = new Person(22); stdout.printf("%d\n", per.age); return 0; } with the command valac helloworld.vala --gir=Hello-1.0.gir doesn't create the Hello-1.0.gir file as one would expect. How can I generate the gir file?

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• C# problem with two threads and hardware access

  - by mack369

  I'm creating an application which communicates with the device via FT2232H USB/RS232 converter. For communication I'm using FTD2XX_NET.dll library from FTDI website. I'm using two threads: first thread continuously reads data from the device the second thread is the main thread of the Windows Form Application I've got a problem when I'm trying to write any data to the device while the receiver's thread is running. The main thread simply hangs up on ftdiDevice.Write function. I tried to synchronize both threads so that only one thread can use Read/Write function at the same time, but it didn't help. Below code responsible for the communication. Note that following functions are methods of FtdiPort class. Receiver's thread private void receiverLoop() { if (this.DataReceivedHandler == null) { throw new BackendException("dataReceived delegate is not set"); } FTDI.FT_STATUS ftStatus = FTDI.FT_STATUS.FT_OK; byte[] readBytes = new byte[this.ReadBufferSize]; while (true) { lock (FtdiPort.threadLocker) { UInt32 numBytesRead = 0; ftStatus = ftdiDevice.Read(readBytes, this.ReadBufferSize, ref numBytesRead); if (ftStatus == FTDI.FT_STATUS.FT_OK) { this.DataReceivedHandler(readBytes, numBytesRead); } else { Trace.WriteLine(String.Format("Couldn't read data from ftdi: status {0}", ftStatus)); Thread.Sleep(10); } } Thread.Sleep(this.RXThreadDelay); } } Write function called from main thread public void Write(byte[] data, int length) { if (this.IsOpened) { uint i = 0; lock (FtdiPort.threadLocker) { this.ftdiDevice.Write(data, length, ref i); } Thread.Sleep(1); if (i != (int)length) { throw new BackendException("Couldnt send all data"); } } else { throw new BackendException("Port is closed"); } } Object used to synchronize two threads static Object threadLocker = new Object(); Method that starts the receiver's thread private void startReceiver() { if (this.DataReceivedHandler == null) { return; } if (this.IsOpened == false) { throw new BackendException("Trying to start listening for raw data while disconnected"); } this.receiverThread = new Thread(this.receiverLoop); //this.receiverThread.Name = "protocolListener"; this.receiverThread.IsBackground = true; this.receiverThread.Start(); } The ftdiDevice.Write function doesn't hang up if I comment following line: ftStatus = ftdiDevice.Read(readBytes, this.ReadBufferSize, ref numBytesRead);

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• Arraylist is null; I cannot access books in the arraylist

  - by user3701380

  I am a beginner-intermediate java programmer and I am getting a null pointer exception from my arraylist. I am writing a bookstore program for APCS and when i add the book, it is supposed to add to the arraylist in the inventory class. But when i call a method to search for a book (e.g. by title), it shows that there isn't anything in the arraylist. //Here is my inventory class -- it has all methods for adding the book or searching for one The searching methods are in getBookByTitle, getBookByAuthor, and getBookByISBN and the method for adding a book is addBook package webbazonab; //Inventory Class //Bharath Senthil //Ansh Sikka import java.util.ArrayList; public class Inventory{ private ArrayList<Book> allBooks = new ArrayList<Book>(); private String bookTitles; private String bookAuthors; private String bookPrices; private String bookCopies; private String ISBNs; public Inventory() { } //@param double price, int copies, String bookTitle, String Author, String isbnNumber public void addBooks(Book addedBook){ allBooks.add(addedBook); } public boolean isAvailable(){ for(Book myBook : allBooks){ if(myBook.copiesLeft() == 0) return false; } return true; } public String populateTitle(){ for (Book titleBooks : allBooks){ bookTitles = titleBooks.getTitle() + "\n"; return bookTitles; } return bookTitles; } public String populateAuthor(){ for(Book authorBooks : allBooks){ bookAuthors = authorBooks.getAuthor() + "\n"; return bookAuthors; } return bookAuthors; } public String populatePrice(){ for (Book pricedBooks : allBooks){ bookPrices = String.valueOf(pricedBooks.getPrice()) + "\n"; } return "$" + bookPrices; } /** * * @return */ public String populateCopies(){ for (Book amtBooks : allBooks){ bookCopies = String.valueOf(amtBooks.copiesLeft()) + "\n"; return bookCopies; } return bookCopies; } public String populateISBN(){ for (Book isbnNums : allBooks){ ISBNs = isbnNums.getIsbn() + "\n"; return ISBNs; } return ISBNs; } @SuppressWarnings("empty-statement") public Book getBookByTitle(String titleSearch) { for(Book titleBook : allBooks) { if (titleBook.getTitle().equals(titleSearch)) { return titleBook; } } return null; } public Book getBookByISBN(String isbnSearch){ for(Book isbnBookSearches : allBooks){ if(isbnBookSearches.getIsbn().equals(isbnSearch)){ return isbnBookSearches; } } return null; } public Book getBookByAuthor(String authorSearch){ for(Book authorBookSearches : allBooks){ if(authorBookSearches.getAuthor().equals(authorSearch)){ return authorBookSearches; } } return null; } public void sort(){ for(int i = 0; i < allBooks.size(); i++) { for(int k = 0; k < allBooks.size(); k++) { if(((Book) allBooks.get(i)).getIsbn().compareTo(((Book) allBooks.get(k)).getIsbn()) < 1) { Book temp = (Book) allBooks.get(k); allBooks.set(k, allBooks.get(i)); allBooks.set(i, temp); } else if(((Book) allBooks.get(i)).getIsbn().compareTo(((Book) allBooks.get(k)).getIsbn()) > 1) { Book temp = (Book) allBooks.get(i); allBooks.set(i, allBooks.get(k)); allBooks.set(k, temp); } } } } public ArrayList<Book> getBooks(){ return allBooks; } } //The exception occurs when i call the method here (in another class): Inventory lib = new Inventory(); jTextField12.setText(lib.getBookByAuthor(authorSearch).getTitle()); Here is my book class if you need it package webbazonab; //Webbazon AB //Project By: Ansh Sikka and Bharath Senthil public class Book { private double myPrice; private String myTitle; private String bookAuthor; private String isbn; private int myCopies; public Book(double price, int copies, String bookTitle, String Author, String isbnNumber) { myPrice = price; myCopies = copies; myTitle = bookTitle; bookAuthor = Author; isbn = isbnNumber; } public double getPrice() { return myPrice; } public String getIsbn() { return isbn; } public String getTitle() { return myTitle; } public String getAuthor() { return bookAuthor; } public int copiesLeft(){ return myCopies; } public String notFound(){ return "The book you searched for could not be found!"; } public String toString() { return "Title: " + getTitle() + "\nAuthor: " + getAuthor() + "\nNumber of Available Books: " + copiesLeft() + "\nPrice: $" + getPrice(); } } Thanks!

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