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  • java serialization problems with different JVMs

    - by Alberto
    I am having trouble using serialization in Java. I've searched the web for a solution but haven't found an answer yet. The problem is this - I have a Java library (I have the code and I export it to an archive prior to executing the code) which I need to use with two differents JVMs. One JVM is on the server (Ubuntu, running Java(TM) JRE SE Runtime Environment (build 1.7.0_09-b05)) and the other on Android 2.3.3. I compiled the library in Java 1.6. Now, I am trying to import to the client, an object exported from the server, but I receive this error: java.io.InvalidClassException: [Lweka.classifiers.functions.MultilayerPerceptron$NeuralEnd;; Incompatible class (SUID): [Lweka.classifiers.functions.MultilayerPerceptron$NeuralEnd;: static final long serialVersionUID =-359311387972759020L; but expected [Lweka.classifiers.functions.MultilayerPerceptron$NeuralEnd;: static final long serialVersionUID =1920571045915494592L; I do have an explicit serial version UID declared on the class MultilayerPerceptron$NeuralEnd, like this: protected class NeuralEnd extends NeuralConnection { private static final long serialVersionUID = 7305185603191183338L; } Where NeuralConnection implements the java.io.Serializable interface. If I do a serialver on MultilayerPerceptron$NeuralEnd I receive the serialVersionUID which I declared. So, why have both JVMs changed this value? Can you help me? Thanks, Alberto

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  • Android HttpsURLConnection and JSON for new GCM

    - by Ryan Gray
    I'm overhauling certain parts of my app to use the new GCM service to replace C2DM. I simply want to create the JSON request from a Java program for testing and then read the response. As of right now I can't find ANY formatting issues with my JSON request and the google server always return code 400, which indicates a problem with my JSON. http://developer.android.com/guide/google/gcm/gcm.html#server JSONObject obj = new JSONObject(); obj.put("collapse_key", "collapse key"); JSONObject data = new JSONObject(); data.put("info1", "info_1"); data.put("info2", "info 2"); data.put("info3", "info_3"); obj.put("data", data); JSONArray ids = new JSONArray(); ids.add(REG_ID); obj.put("registration_ids", ids); System.out.println(obj.toJSONString()); I print my request to the eclipse console to check it's formatting byte[] postData = obj.toJSONString().getBytes(); try{ URL url = new URL("https://android.googleapis.com/gcm/send"); HttpsURLConnection.setDefaultHostnameVerifier(new JServerHostnameVerifier()); HttpsURLConnection conn = (HttpsURLConnection) url.openConnection(); conn.setDoOutput(true); conn.setDoInput(true); conn.setUseCaches(false); conn.setRequestMethod("POST"); conn.setRequestProperty("Content-Type", "application/json"); conn.setRequestProperty("Authorization", "key=" + API_KEY); System.out.println(conn.toString()); OutputStream out = conn.getOutputStream(); // exception thrown right here. no InputStream to get InputStream in = conn.getInputStream(); byte[] response = null; out.write(postData); out.close(); in.read(response); JSONParser parser = new JSONParser(); String temp = new String(response); JSONObject temp1 = (JSONObject) parser.parse(temp); System.out.println(temp1.toJSONString()); int responseCode = conn.getResponseCode(); System.out.println(responseCode + ""); } catch(Exception e){ System.out.println("Exception thrown\n"+ e.getMessage()); } } I'm sure my API key is correct as that would result in error 401, so says the google documentation. This is my first time doing JSON but it's easy to understand because of its simplicity. Anyone have any ideas on why I always receive code 400? update: I've tested the google server example classes provided with gcm so the problem MUST be with my code.

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  • How to save image drawn on a JPanel?

    - by swift
    I have a panel with transparent background which i use to draw an image. now problem here is when i draw anything on panel and save the image as a JPEG file its saving the image with black background but i want it to be saved as same, as i draw on the panel. what should be done for this? plz guide me j Client.java public class Client extends Thread { static DatagramSocket datasocket; static DatagramSocket socket; Point point; Whiteboard board; Virtualboard virtualboard; JLayeredPane layerpane; BufferedImage image; public Client(DatagramSocket datasocket) { Client.datasocket=datasocket; } //This function is responsible to connect to the server public static void connect() { try { socket=new DatagramSocket (9000); //client connection socket port= 9000 datasocket=new DatagramSocket (9005); //client data socket port= 9002 ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); //this is to tell server that this is a connection request dos.writeChar('c'); dos.close(); byte[]data=baos.toByteArray(); //Server IP address InetAddress ip=InetAddress.getByName("10.123.97.154"); //create the UDP packet DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8000); socket.send(packet); Client client=new Client(datasocket); client.createFrame(); client.run(); } catch(Exception e) { e.printStackTrace(); } } //This function is to create the JFrame public void createFrame() { JFrame frame=new JFrame("Whiteboard"); frame.setVisible(true); frame.setBackground(Color.black); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(680,501); frame.addWindowListener(new WindowAdapter() { public void windowOpened(WindowEvent e) {} public void windowClosing(WindowEvent e) { close(); } }); layerpane=frame.getLayeredPane(); board= new Whiteboard(datasocket); image = new BufferedImage(590,463, BufferedImage.TYPE_INT_ARGB); board.setBounds(74,2,590,463); board.setImage(image); virtualboard=new Virtualboard(); virtualboard.setImage(image); virtualboard.setBounds(74,2,590,463); layerpane.add(virtualboard,new Integer(2));//Panel where remote user draws layerpane.add(board,new Integer(3)); layerpane.add(board.colourButtons(),new Integer(1)); layerpane.add(board.shapeButtons(),new Integer(0)); //frame.add(paper.addButtons(),BorderLayout.WEST); } /* * This function is overridden from the thread class * This function listens for incoming packets from the server * which contains the points drawn by the other client */ public void run () { while (true) { try { byte[] buffer = new byte[512]; DatagramPacket packet = new DatagramPacket(buffer, buffer.length); datasocket.receive(packet); InputStream in=new ByteArrayInputStream(packet.getData(), packet.getOffset(),packet.getLength()); DataInputStream din=new DataInputStream(in); int x=din.readInt(); int y=din.readInt(); String varname=din.readLine(); String var[]=varname.split("-",4); point=new Point(x,y); virtualboard.addPoint(point, var[0], var[1],var[2],var[3]); } catch (IOException ex) { ex.printStackTrace(); } } } //This function is to broadcast the newly drawn point to the server public void broadcast (Point p,String varname,String shape,String event, String color) { try { ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); dos.writeInt(p.x); dos.writeInt(p.y); dos.writeBytes(varname); dos.writeBytes("-"); dos.writeBytes(shape); dos.writeBytes("-"); dos.writeBytes(event); dos.writeBytes("-"); dos.writeBytes(color); dos.close(); byte[]data=baos.toByteArray(); InetAddress ip=InetAddress.getByName("10.123.97.154"); DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8002); datasocket.send(packet); } catch (Exception e) { e.printStackTrace(); } } //This function is to close the client's connection with the server public void close() { try { ByteArrayOutputStream baos=new ByteArrayOutputStream(); DataOutputStream dos=new DataOutputStream(baos); //This is to tell server that this is request to remove the client dos.writeChar('r'); dos.close(); byte[]data=baos.toByteArray(); //Server IP address InetAddress ip=InetAddress.getByName("10.123.97.154"); DatagramPacket packet=new DatagramPacket(data, data.length,ip , 8000); socket.send(packet); System.out.println("closed"); } catch(Exception e) { e.printStackTrace(); } } public static void main(String[] args) throws Exception { connect(); } } Whiteboard.java class Whiteboard extends JPanel implements MouseListener,MouseMotionListener,ActionListener,KeyListener { BufferedImage image; Boolean tooltip=false; int post; String shape; String selectedcolor="black"; Color color=Color.black; //Color color=Color.white; Point start; Point end; Point mp; Point tip; int keycode; String fillshape; Point fillstart=new Point(); Point fillend=new Point(); int noofside; Button r=new Button("rect"); Button rectangle=new Button("rect"); Button line=new Button("line"); Button roundrect=new Button("roundrect"); Button polygon=new Button("poly"); Button text=new Button("text"); JButton save=new JButton("Save"); Button elipse=new Button("elipse"); ImageIcon fillicon=new ImageIcon("images/fill.jpg"); JButton fill=new JButton(fillicon); ImageIcon erasericon=new ImageIcon("images/eraser.gif"); JButton erase=new JButton(erasericon); JButton[] colourbutton=new JButton[28]; String selected; Point label; String key=""; int ex,ey;//eraser DatagramSocket dataSocket; JButton button = new JButton("test"); Client client; Boolean first; int w,h; public Whiteboard(DatagramSocket dataSocket) { try { UIManager.setLookAndFeel( UIManager.getCrossPlatformLookAndFeelClassName()); } catch (Exception e) { e.printStackTrace(); } setLayout(null); setOpaque(false); setBackground(new Color(237,237,237)); this.dataSocket=dataSocket; client=new Client(dataSocket); addKeyListener(this); addMouseListener(this); addMouseMotionListener(this); setBorder(BorderFactory.createLineBorder(Color.black)); } public void paintComponent(Graphics g) { try { super.paintComponent(g); g.drawImage(image, 0, 0, this); Graphics2D g2 = (Graphics2D)g; if(color!=null) g2.setPaint(color); if(start!=null && end!=null) { if(selected==("elipse")) g2.drawOval(start.x, start.y,(end.x-start.x),(end.y-start.y)); else if(selected==("rect")) g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected==("rrect")) g2.drawRoundRect(start.x, start.y, (end.x-start.x),(end.y-start.y),11,11); else if(selected==("line")) g2.drawLine(start.x,start.y,end.x,end.y); else if(selected==("poly")) { g2.drawLine(start.x,start.y,end.x,end.y); client.broadcast(start, "start", "poly", "drag", selectedcolor); client.broadcast(end, "end", "poly", "drag", selectedcolor); } } if(tooltip==true) { System.out.println(selected); if(selected=="text") { g2.drawString("|", tip.x, tip.y-5); g2.drawString("Click to add text", tip.x+10, tip.y+23); g2.drawString("__", label.x+post, label.y); } if(selected=="erase") { g2.setPaint(new Color(237,237,237)); g2.fillRect(tip.x-10,tip.y-10,10,10); g2.setPaint(color); g2.drawRect(tip.x-10,tip.y-10,10,10); } } } catch(Exception e) {} } //Function to draw the shape on image public void draw() { Graphics2D g2 = (Graphics2D) image.createGraphics(); Font font=new Font("Times New Roman",Font.PLAIN,14); g2.setFont(font); g2.setPaint(color); if(start!=null && end!=null) { if(selected=="line") g2.drawLine(start.x, start.y, end.x, end.y); else if(selected=="elipse") g2.drawOval(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected=="rect") g2.drawRect(start.x, start.y, (end.x-start.x),(end.y-start.y)); else if(selected==("rrect")) g2.drawRoundRect(start.x, start.y, (end.x-start.x),(end.y-start.y),11,11); else if(selected==("poly")) { g2.drawLine(start.x,start.y,end.x,end.y); client.broadcast(start, "start", "poly", "release", selectedcolor); client.broadcast(end, "end", "poly", "release", selectedcolor); } fillstart=start; fillend=end; fillshape=selected; } if(selected!="poly") { start=null; end=null; } if(label!=null) { if(selected==("text")) { g2.drawString(key,label.x,label.y); client.broadcast(label, key, "text", "release", selectedcolor); } } repaint(); g2.dispose(); } //Function which provides the erase functionality public void erase() { Graphics2D pic=(Graphics2D) image.createGraphics(); Color erasecolor=new Color(237,237,237); pic.setPaint(erasecolor); if(start!=null) pic.fillRect(start.x-10, start.y-10, 10, 10); } //To set the size of the image public void setImage(BufferedImage image) { this.image = image; } //Function to add buttons into the panel, calling this function returns a panel public JPanel shapeButtons() { JPanel shape=new JPanel(); shape.setBackground(new Color(181, 197, 210)); shape.setLayout(new GridLayout(5,2,2,4)); shape.setBounds(0, 2, 74, 166); rectangle.addActionListener(this); rectangle.setToolTipText("Rectangle"); line.addActionListener( this); line.setToolTipText("Line"); erase.addActionListener(this); erase.setToolTipText("Eraser"); roundrect.addActionListener(this); roundrect.setToolTipText("Round edge Rectangle"); polygon.addActionListener(this); polygon.setToolTipText("Polygon"); text.addActionListener(this); text.setToolTipText("Text"); fill.addActionListener(this); fill.setToolTipText("Fill with colour"); elipse.addActionListener(this); elipse.setToolTipText("Elipse"); save.addActionListener(this); shape.add(elipse); shape.add(rectangle); shape.add(roundrect); shape.add(polygon); shape.add(line); shape.add(text); shape.add(fill); shape.add(erase); shape.add(save); return shape; } public JPanel colourButtons() { JPanel colourbox=new JPanel(); colourbox.setBackground(new Color(181, 197, 210)); colourbox.setLayout(new GridLayout(8,2,8,8)); colourbox.setBounds(0,323,70,140); //colourbox.add(empty); for(int i=0;i<16;i++) { colourbutton[i]=new JButton(); colourbox.add(colourbutton[i]); if(i==0) colourbutton[0].setBackground(Color.black); else if(i==1) colourbutton[1].setBackground(Color.white); else if(i==2) colourbutton[2].setBackground(Color.red); else if(i==3) colourbutton[3].setBackground(Color.orange); else if(i==4) colourbutton[4].setBackground(Color.blue); else if(i==5) colourbutton[5].setBackground(Color.green); else if(i==6) colourbutton[6].setBackground(Color.pink); else if(i==7) colourbutton[7].setBackground(Color.magenta); else if(i==8) colourbutton[8].setBackground(Color.cyan); else if(i==9) colourbutton[9].setBackground(Color.black); else if(i==10) colourbutton[10].setBackground(Color.yellow); else if(i==11) colourbutton[11].setBackground(new Color(131,168,43)); else if(i==12) colourbutton[12].setBackground(new Color(132,0,210)); else if(i==13) colourbutton[13].setBackground(new Color(193,17,92)); else if(i==14) colourbutton[14].setBackground(new Color(129,82,50)); else if(i==15) colourbutton[15].setBackground(new Color(64,128,128)); colourbutton[i].addActionListener(this); } return colourbox; } public void fill() { if(selected=="fill") { Graphics2D g2 = (Graphics2D) image.getGraphics(); g2.setPaint(color); System.out.println("Fill"); if(fillshape=="elipse") g2.fillOval(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y)); else if(fillshape=="rect") g2.fillRect(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y)); else if(fillshape==("rrect")) g2.fillRoundRect(fillstart.x, fillstart.y, (fillend.x-fillstart.x),(fillend.y-fillstart.y),11,11); // else if(fillshape==("poly")) // g2.drawPolygon(x,y,2); } repaint(); } //To save the image drawn public void save() { try { ByteArrayOutputStream bos = new ByteArrayOutputStream(); JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(bos); JFileChooser fc = new JFileChooser(); fc.showSaveDialog(this); encoder.encode(image); byte[] jpgData = bos.toByteArray(); FileOutputStream fos = new FileOutputStream(fc.getSelectedFile()+".jpeg"); fos.write(jpgData); fos.close(); //add replce confirmation here } catch (IOException e) { System.out.println(e); } } public void mouseClicked(MouseEvent e) { } @Override public void mouseEntered(MouseEvent e) { } public void mouseExited(MouseEvent arg0) { } public void mousePressed(MouseEvent e) { if(selected=="line"||selected=="text") { start=e.getPoint(); client.broadcast(start,"start", selected,"press", selectedcolor); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") mp = e.getPoint(); else if(selected=="poly") { if(first==true) { start=e.getPoint(); //client.broadcast(start,"start", selected,"press", selectedcolor); } else if(first==false) { end=e.getPoint(); repaint(); //client.broadcast(end,"end", selected,"press", selectedcolor); } } else if(selected=="erase") { start=e.getPoint(); erase(); } } public void mouseReleased(MouseEvent e) { if(selected=="text") { System.out.println("Reset"); key=""; post=0; label=new Point(); label=e.getPoint(); grabFocus(); } if(start!=null && end!=null) { if(selected=="line") { end=e.getPoint(); client.broadcast(end,"end", selected,"release", selectedcolor); draw(); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") { end.x = Math.max(mp.x,e.getX()); end.y = Math.max(mp.y,e.getY()); client.broadcast(end,"end", selected,"release", selectedcolor); draw(); } else if(selected=="poly") { draw(); first=false; start=end; end=null; } } } public void mouseDragged(MouseEvent e) { if(end==null) end = new Point(); if(start==null) start = new Point(); if(selected=="line") { end=e.getPoint(); client.broadcast(end,"end", selected,"drag", selectedcolor); } else if(selected=="erase") { start=e.getPoint(); erase(); client.broadcast(start,"start", selected,"drag", selectedcolor); } else if(selected=="elipse"||selected=="rect"||selected=="rrect") { start.x = Math.min(mp.x,e.getX()); start.y = Math.min(mp.y,e.getY()); end.x = Math.max(mp.x,e.getX()); end.y = Math.max(mp.y,e.getY()); client.broadcast(start,"start", selected,"drag", selectedcolor); client.broadcast(end,"end", selected,"drag", selectedcolor); } else if(selected=="poly") end=e.getPoint(); System.out.println(tooltip); if(tooltip==true) { if(selected=="erase") { Graphics2D g2=(Graphics2D) getGraphics(); tip=e.getPoint(); g2.drawRect(tip.x-10,tip.y-10,10,10); } } repaint(); } public void mouseMoved(MouseEvent e) { if(selected=="text" ||selected=="erase") { tip=new Point(); tip=e.getPoint(); tooltip=true; repaint(); } } public void actionPerformed(ActionEvent e) { if(e.getSource()==elipse) selected="elipse"; else if(e.getSource()==line) selected="line"; else if(e.getSource()==rectangle) selected="rect"; else if(e.getSource()==erase) { selected="erase"; tooltip=true; System.out.println(selected); erase(); } else if(e.getSource()==roundrect) selected="rrect"; else if(e.getSource()==polygon) { selected="poly"; first=true; start=null; } else if(e.getSource()==text) { selected="text"; tooltip=true; } else if(e.getSource()==fill) { selected="fill"; fill(); } else if(e.getSource()==save) save(); if(e.getSource()==colourbutton[0]) { color=Color.black; selectedcolor="black"; } else if(e.getSource()==colourbutton[1]) { color=Color.white; selectedcolor="white"; } else if(e.getSource()==colourbutton[2]) { color=Color.red; selectedcolor="red"; } else if(e.getSource()==colourbutton[3]) { color=Color.orange; selectedcolor="orange"; } else if(e.getSource()==colourbutton[4]) { selectedcolor="blue"; color=Color.blue; } else if(e.getSource()==colourbutton[5]) { selectedcolor="green"; color=Color.green; } else if(e.getSource()==colourbutton[6]) { selectedcolor="pink"; color=Color.pink; } else if(e.getSource()==colourbutton[7]) { selectedcolor="magenta"; color=Color.magenta; } else if(e.getSource()==colourbutton[8]) { selectedcolor="cyan"; color=Color.cyan; } } @Override public void keyPressed(KeyEvent e) { //System.out.println(e.getKeyChar()+" : "+e.getKeyCode()); if(label!=null) { if(e.getKeyCode()==10) //Check for Enter key { label.y=label.y+14; key=""; post=0; repaint(); } else if(e.getKeyCode()==8) //Backspace { try{ Graphics2D g2 = (Graphics2D) image.getGraphics(); g2.setPaint(new Color(237,237,237)); g2.fillRect(label.x+post-7, label.y-13, 14, 17); if(post>0) post=post-6; keycode=0; key=key.substring(0, key.length()-1); System.out.println(key.substring(0, key.length())); repaint(); Point broadcastlabel=new Point(); broadcastlabel.x=label.x+post-7; broadcastlabel.y=label.y-13; client.broadcast(broadcastlabel, key, "text", "backspace", selectedcolor); } catch(Exception ex) {} } //Block invalid keys else if(!(e.getKeyCode()>=16 && e.getKeyCode()<=20 || e.getKeyCode()>=112 && e.getKeyCode()<=123 || e.getKeyCode()>=33 && e.getKeyCode()<=40 || e.getKeyCode()>=144 && e.getKeyCode()<=145 || e.getKeyCode()>=524 && e.getKeyCode()<=525 ||e.getKeyCode()==27||e.getKeyCode()==155 ||e.getKeyCode()==127)) { key=key+e.getKeyChar(); post=post+6; draw(); } } } @Override public void keyReleased(KeyEvent e) { } @Override public void keyTyped(KeyEvent e) { } } class Button extends JButton { String name; int i; public Button(String name) { this.name=name; try { UIManager.setLookAndFeel("com.sun.java.swing.plaf.windows.WindowsLookAndFeel"); } catch (Exception e) { e.printStackTrace(); } } public Button(int i) { this.i=i; } public void paintComponent(Graphics g) { super.paintComponent(g); Graphics2D g2 = (Graphics2D)g; g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON); //g2.setStroke(new BasicStroke(1.2f)); if (name == "line") g.drawLine(5,5,30,30); if (name == "elipse") g.drawOval(5,7,25,20); if (name== "rect") g.drawRect(5,5,25,23); if (name== "roundrect") g.drawRoundRect(5,5,25,23,10,10); int a[]=new int[]{20,9,20,23,20}; int b[]=new int[]{9,23,25,20,9}; if (name== "poly") g.drawPolyline(a, b, 5); if (name== "text") g.drawString("Text",8, 24); } }

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  • Is 1/0 a legal Java expression?

    - by polygenelubricants
    The following compiles fine in my Eclipse: final int j = 1/0; // compiles fine!!! // throws ArithmeticException: / by zero at run-time Java prevents many "dumb code" from even compiling in the first place (e.g. "Five" instanceof Number doesn't compile!), so the fact this didn't even generate as much as a warning was very surprising to me. The intrigue deepens when you consider the fact that constant expressions are allowed to be optimized at compile time: public class Div0 { public static void main(String[] args) { final int i = 2+3; final int j = 1/0; final int k = 9/2; } } Compiled in Eclipse, the above snippet generates the following bytecode (javap -c Div0) Compiled from "Div0.java" public class Div0 extends java.lang.Object{ public Div0(); Code: 0: aload_0 1: invokespecial #8; //Method java/lang/Object."<init>":()V 4: return public static void main(java.lang.String[]); Code: 0: iconst_5 1: istore_1 // "i = 5;" 2: iconst_1 3: iconst_0 4: idiv 5: istore_2 // "j = 1/0;" 6: iconst_4 7: istore_3 // "k = 4;" 8: return } As you can see, the i and k assignments are optimized as compile-time constants, but the division by 0 (which must've been detectable at compile-time) is simply compiled as is. javac 1.6.0_17 behaves even more strangely, compiling silently but excising the assignments to i and k completely out of the bytecode (probably because it determined that they're not used anywhere) but leaving the 1/0 intact (since removing it would cause an entirely different program semantics). So the questions are: Is 1/0 actually a legal Java expression that should compile anytime anywhere? What does JLS say about it? If this is legal, is there a good reason for it? What good could this possibly serve?

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  • Some help required while working on Java and Cygwin together

    - by Hippo
    Hello .. I am new to java and also cygwin . I do not have in detailed knowledge of both . I need some help.. I simple steps i will try to explain my problem. 1) I am working on tinyOS . its open source OS , used for wireless sensor networks. It provides java libraries to work on communication (PC to sensor) 2) I am working on windows xp environment through cigwin. 3) I am developing an application . THis application requires one java interface called "Serial Forwarder" , which is readily available in libraries provided. Previously i used to start this interface manually (by entering command *"java net.tinyos.sf.SerialForwarder ")*and then my application which uses this interface. But now i want to make my application independent . User need know about this background cygwin commands . 4) So in my java application i used "Runtime.getRuntime().exec( "java net.tinyos.sf.SerialForwarder)" . 5) This i neither giving any error nor starting the interface. Am I going on right way ? When i am using runtime execute command , how can i make sure that this command is called through cigwin interface ? Also .. if i want to write .bat file .. i which i can give commands which will be executed .. how can i make sure that those commands are given through cigwin .. and not through cmd.exe .. Please help . me .

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  • Working with mongodb from Java

    - by demas
    I have launch mongodb server: [[email protected]][~]% mongod --dbpatmongod --dbpath /home/demas/temp/ Mon Apr 19 09:44:18 Mongo DB : starting : pid = 4538 port = 27017 dbpath = /home/demas/temp/ master = 0 slave = 0 32-bit ** NOTE: when using MongoDB 32 bit, you are limited to about 2 gigabytes of data ** see http://blog.mongodb.org/post/137788967/32-bit-limitations for more Mon Apr 19 09:44:18 db version v1.4.0, pdfile version 4.5 Mon Apr 19 09:44:18 git version: nogitversion Mon Apr 19 09:44:18 sys info: Linux arch.local.net 2.6.33-ARCH #1 SMP PREEMPT Mon Apr 5 05:57:38 UTC 2010 i686 BOOST_LIB_VERSION=1_41 Mon Apr 19 09:44:18 waiting for connections on port 27017 Mon Apr 19 09:44:18 web admin interface listening on port 28017 I have created documents by console client: [[email protected]][~]% mongo MongoDB shell version: 1.4.0 url: test connecting to: test type "help" for help > db.some.find(); { "_id" : ObjectId("4bcbef3c3be43e9b7e04ef3d"), "name" : "mongo" } { "_id" : ObjectId("4bcbef423be43e9b7e04ef3e"), "x" : 3 } Now I am trying to work with MongoDb from Java: import com.mongodb.*; import java.net.UnknownHostException; public class test1 { public static void main(String[] args) { System.out.println("Start"); try { Mongo m = new Mongo("localhost", 27017); DB db = m.getDB("test"); DBCollection coll = db.getCollection("some"); coll.insert(makeDocument(10, "James", "male")); System.out.println("Finish"); } catch (UnknownHostException ex) { ex.printStackTrace(); } catch (MongoException ex) { ex.printStackTrace(); } } public static BasicDBObject makeDocument(int id, String name, String gender) { BasicDBObject doc = new BasicDBObject(); doc.put("id", id); doc.put("name", name); doc.put("gender", gender); return doc; } } But execution stops on line coll.insert(): [[email protected]][~/dev/study/java/mongodb]% javac test1.java [[email protected]][~/dev/study/java/mongodb]% java test1 Start There are not messages from mogodb server regarding accepted connection. Why?

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  • Calling Java classes from IzPack

    - by bguiz
    I am trying to write an IzPack installer which is able to detect a previously installed version of the application. After finding out that it doesn't really support this feature, I think the only way to do this is through writing a Java class and calling it from IzPack. Tim Williscroft has previously suggested this method: <condition type="java" id="jbossEnv"> <java> <class>au.com.codarra.ela.installer.JBossChecker</class <field>hasJBossEnv</field> </java> <returnvalue type="boolean">true</returnvalue> </condition> However, is it possible to call <java> from somewhere other than a <condition> tag? I want to be able to call it from a <variable> tag. Also, is it possible to call a method from a Java class instead of reading a value of a field? I want to be able to pass parameters to my class. Thank you!

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  • Java: how to get all subdirs recursively?

    - by HH
    Before debugging the late-hour-out-of-bound-recursive-function: is there a command to get subdirs? giveMeSubDirs(downToPath)? // WARNING: RECURSION out of bound public HashSet<FileObject> getAllDirs(String path) { HashSet<FileObject> checkedDirs = new HashSet<FileObject>(); HashSet<FileObject> allDirs = new HashSet<FileObject>(); String startingPath = path; File fileThing = new File(path); FileObject fileObject = new FileObject(fileThing); for (FileObject dir : getDirsInDir(path)) { // SUBDIR while ( !checkedDirs.contains(dir) && !(getDirsInDir(dir.getFile().getParent()).size() == 0)) { // DO NOT CHECK TOP DIRS if any bottom dir UNCHECKED! while ( uncheckedDirsOnLevel(path, checkedDirs).size() > 0) { while (getDirsInDir(path).size() == 0 || (numberOfCheckedDirsOnLevel(path, checkedDirs)==getDirsInDir(path).size())) { allDirs.add(new FileObject(new File(path))); checkedDirs.add(new FileObject(new File(path))); if(traverseDownOneLevel(path) == startingPath ) return allDirs; //get nearer to the root path = traverseDownOneLevel(path); } path = giveAnUncheckedDir(path, checkedDirs); if ( path == "NoUnchecked.") { checkedDirs.add(new FileObject( (new File(path)).getParentFile() )); break; } } } } return allDirs; }

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  • AES decryption in Java - IvParameterSpec to big

    - by user1277269
    Im going to decrypt a plaintext with two keys. As you see in the picture were have one encrypted file wich contains KEY1(128 bytes),KEYIV(128 bytes),key2(128bytes) wich is not used in this case then we have the ciphertext. The error I get here is "Exception in thread "main" java.security.InvalidAlgorithmParameterException: Wrong IV length: must be 16 bytes long. but it is 64 bytes." Picture: http://i264.photobucket.com/albums/ii200/XeniuM05/bg_zps0a523659.png public class AES { public static void main(String[] args) throws Exception { byte[] encKey1 = new byte[128]; byte[] EncIV = new byte[256]; byte[] UnEncIV = new byte[128]; byte[] unCrypKey = new byte[128]; byte[] unCrypText = new byte[1424]; File f = new File("C://ftp//ciphertext.enc"); FileInputStream fis = new FileInputStream(F); byte[] EncText = new byte[(int) f.length()]; fis.read(encKey1); fis.read(EncIV); fis.read(EncText); EncIV = Arrays.copyOfRange(EncIV, 128, 256); EncText = Arrays.copyOfRange(EncText, 384, EncText.length); System.out.println(EncText.length); KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType()); char[] password = "lab1StorePass".toCharArray(); java.io.FileInputStream fos = new java.io.FileInputStream( "C://ftp//lab1Store"); ks.load(fos, password); char[] passwordkey1 = "lab1KeyPass".toCharArray(); PrivateKey Lab1EncKey = (PrivateKey) ks.getKey("lab1EncKeys", passwordkey1); Cipher rsaDec = Cipher.getInstance("RSA"); // set cipher to RSA decryption rsaDec.init(Cipher.DECRYPT_MODE, Lab1EncKey); // initalize cipher ti lab1key unCrypKey = rsaDec.doFinal(encKey1); // Decryps first key UnEncIV = rsaDec.doFinal(EncIV); //decryps encive byte array to undecrypted bytearray---- OBS! Error this is 64 BYTES big, we want 16? System.out.println("lab1key "+ unCrypKey +" IV " + UnEncIV); //-------CIPHERTEXT decryption--------- Cipher AESDec = Cipher.getInstance("AES/CBC/PKCS5Padding"); //---------convert decrypted bytearrays to acctual keys SecretKeySpec unCrypKey1 = new SecretKeySpec(unCrypKey, "AES"); IvParameterSpec ivSpec = new IvParameterSpec(UnEncIV); AESDec.init(Cipher.DECRYPT_MODE, unCrypKey1, ivSpec ); unCrypText = AESDec.doFinal(EncText); // Convert decrypted cipher bytearray to string String deCryptedString = new String(unCrypKey); System.out.println(deCryptedString); }

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  • Java constructor and modify the object properties at runtime

    - by lupin
    Note: This is an assignment Hi, I have the following class/constructor. import java.io.*; class Set { public int numberOfElements = 0; public String[] setElements = new String[5]; public int maxNumberOfElements = 5; // constructor for our Set class public Set(int numberOfE, int setE, int maxNumberOfE) { int numberOfElements = numberOfE; String[] setElements = new String[setE]; int maxNumberOfElements = maxNumberOfE; } // Helper method to shorten/remove element of array since we're using basic array instead of ArrayList or HashSet from collection interface :( static String[] removeAt(int k, String[] arr) { final int L = arr.length; String[] ret = new String[L - 1]; System.arraycopy(arr, 0, ret, 0, k); System.arraycopy(arr, k + 1, ret, k, L - k - 1); return ret; } int findElement(String element) { int retval = 0; for ( int i = 0; i < setElements.length; i++) { if ( setElements[i] != null && setElements[i].equals(element) ) { return retval = i; } retval = -1; } return retval; } void add(String newValue) { int elem = findElement(newValue); if( numberOfElements < maxNumberOfElements && elem == -1 ) { setElements[numberOfElements] = newValue; numberOfElements++; } } int getLength() { if ( setElements != null ) { return setElements.length; } else { return 0; } } String[] emptySet() { setElements = new String[0]; return setElements; } Boolean isFull() { Boolean True = new Boolean(true); Boolean False = new Boolean(false); if ( setElements.length == maxNumberOfElements ){ return True; } else { return False; } } Boolean isEmpty() { Boolean True = new Boolean(true); Boolean False = new Boolean(false); if ( setElements.length == 0 ) { return True; } else { return False; } } void remove(String newValue) { for ( int i = 0; i < setElements.length; i++) { if ( setElements[i].equals(newValue) ) { setElements = removeAt(i,setElements); } } } int isAMember(String element) { int retval = -1; for ( int i = 0; i < setElements.length; i++ ) { if (setElements[i] != null && setElements[i].equals(element)) { return retval = i; } } return retval; } void printSet() { for ( int i = 0; i < setElements.length; i++) { System.out.println("Member elements on index: "+ i +" " + setElements[i]); } } String[] getMember() { String[] tempArray = new String[setElements.length]; for ( int i = 0; i < setElements.length; i++) { if(setElements[i] != null) { tempArray[i] = setElements[i]; } } return tempArray; } Set union(Set x, Set y) { String[] newXtemparray = new String[x.getLength()]; String[] newYtemparray = new String[y.getLength()]; Set temp = new Set(1,20,20); newXtemparray = x.getMember(); newYtemparray = x.getMember(); for(int i = 0; i < newXtemparray.length; i++) { temp.add(newYtemparray[i]); } for(int j = 0; j < newYtemparray.length; j++) { temp.add(newYtemparray[j]); } return temp; } } // This is the SetDemo class that will make use of our Set class class SetDemo { public static void main(String[] args) { //get input from keyboard BufferedReader keyboard; InputStreamReader reader; String temp = ""; reader = new InputStreamReader(System.in); keyboard = new BufferedReader(reader); try { System.out.println("Enter string element to be added" ); temp = keyboard.readLine( ); System.out.println("You entered " + temp ); } catch (IOException IOerr) { System.out.println("There was an error during input"); } /* ************************************************************************** * Test cases for our new created Set class. * ************************************************************************** */ Set setA = new Set(1,10,10); setA.add(temp); setA.add("b"); setA.add("b"); setA.add("hello"); setA.add("world"); setA.add("six"); setA.add("seven"); setA.add("b"); int size = setA.getLength(); System.out.println("Set size is: " + size ); Boolean isempty = setA.isEmpty(); System.out.println("Set is empty? " + isempty ); int ismember = setA.isAMember("sixb"); System.out.println("Element six is member of setA? " + ismember ); Boolean output = setA.isFull(); System.out.println("Set is full? " + output ); setA.printSet(); int index = setA.findElement("world"); System.out.println("Element b located on index: " + index ); setA.remove("b"); setA.emptySet(); int resize = setA.getLength(); System.out.println("Set size is: " + resize ); setA.printSet(); Set setB = new Set(0,10,10); Set SetA = setA.union(setB,setA); SetA.printSet(); } } I have two question here, why I when I change the class property declaration to: class Set { public int numberOfElements; public String[] setElements; public int maxNumberOfElements; // constructor for our Set class public Set(int numberOfE, int setE, int maxNumberOfE) { int numberOfElements = numberOfE; String[] setElements = new String[setE]; int maxNumberOfElements = maxNumberOfE; } I got this error: \ javaprojects>java SetDemo Enter string element to be added a You entered a Exception in thread "main" java.lang.NullPointerException at Set.findElement(Set.java:30) at Set.add(Set.java:43) at SetDemo.main(Set.java:169) Second, on the union method, why the result of SetA.printSet still printing null, isn't it getting back the return value from union method? Thanks in advance for any explaination. lupin

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  • Performance of Java matrix math libraries?

    - by dfrankow
    We are computing something whose runtime is bound by matrix operations. (Some details below if interested.) This experience prompted the following question: Do folk have experience with the performance of Java libraries for matrix math (e.g., multiply, inverse, etc.)? For example: JAMA: http://math.nist.gov/javanumerics/jama/ COLT: http://acs.lbl.gov/~hoschek/colt/ Apache commons math: http://commons.apache.org/math/ I searched and found nothing. Details of our speed comparison: We are using Intel FORTRAN (ifort (IFORT) 10.1 20070913). We have reimplemented it in Java (1.6) using Apache commons math 1.2 matrix ops, and it agrees to all of its digits of accuracy. (We have reasons for wanting it in Java.) (Java doubles, Fortran real*8). Fortran: 6 minutes, Java 33 minutes, same machine. jvisualm profiling shows much time spent in RealMatrixImpl.{getEntry,isValidCoordinate} (which appear to be gone in unreleased Apache commons math 2.0, but 2.0 is no faster). Fortran is using Atlas BLAS routines (dpotrf, etc.). Obviously this could depend on our code in each language, but we believe most of the time is in equivalent matrix operations. In several other computations that do not involve libraries, Java has not been much slower, and sometimes much faster.

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  • ClassNotFoundException com.mysql.jdbc.Driver

    - by Dusk
    This question might have asked here number of times . After doing some google search for the above error and doing some update, I can't understand why I'm still getting that error. I've already put my driver-- mysql-connector-java-5.1.5-bin in the classpath: Java_Home\jre\lib\ Java_Home\jre\lib\ext\ Java_Home\lib and the code which I'm using to connect to mysql database is: try{ Class.forName("com.mysql.jdbc.Driver"); Connection con=DriverManager.getConnection("jdbc:mysql://localhost:3306/mail","root",""); Statement stmt = con.createStatement(); ResultSet rs = stmt.executeQuery("select message_body from deadletter"); String dbtime; while (rs.next()) { dbtime = rs.getString(1); System.out.println(dbtime); } con.close(); } catch (SQLException e) { System.out.println("Connection Failed! Check output console"); e.printStackTrace(); } } and the complete stacktrace of the above exception is: java.lang.ClassNotFoundException: com.mysql.jdbc:Driver at java.net.URLClassLoader$1.run(URLClassLoader.java:200) at java.security.AccessController.doPrivileged(Native Method) at java.net.URLClassLoader.findClass(URLClassLoader.java:307) at java.lang.ClassLoader.loadClass(ClassLoader.java:307) at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:301) at java.lang.ClassLoader.loadClass(ClassLoader.java:252) at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:320) at java.lang.Class.forName0(Native Method) at java.lang.Class.forName(Class.java:169) at mail.main(mail.java:114) Now, what's wrong I'm doing here?

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  • Cannot run public class in one .java from another

    - by DIOS
    I have created a basic program that takes whatever is input into two textfields and exports them to a file. I would now like to encrypt that file, and alredy have the encryptor. The problem is that I cannot call it. Here is my code for the encryptor: import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.*; import javax.crypto.Cipher; import javax.crypto.CipherInputStream; import javax.crypto.CipherOutputStream; import javax.crypto.spec.SecretKeySpec; public class FileEncryptor { private String algo; private File file; public FileEncryptor(String algo,String path) { this.algo=algo; //setting algo this.file=new File(path); //settong file } public void encrypt() throws Exception{ //opening streams FileInputStream fis =new FileInputStream(file); file=new File(file.getAbsolutePath()); FileOutputStream fos =new FileOutputStream(file); //generating key byte k[] = "HignDlPs".getBytes(); SecretKeySpec key = new SecretKeySpec(k,algo.split("/")[0]); //creating and initialising cipher and cipher streams Cipher encrypt = Cipher.getInstance(algo); encrypt.init(Cipher.ENCRYPT_MODE, key); CipherOutputStream cout=new CipherOutputStream(fos, encrypt); byte[] buf = new byte[1024]; int read; while((read=fis.read(buf))!=-1) //reading data cout.write(buf,0,read); //writing encrypted data //closing streams fis.close(); cout.flush(); cout.close(); } public static void main (String[] args)throws Exception { new FileEncryptor("DES/ECB/PKCS5Padding","C:\\Users\\*******\\Desktop\\newtext").encrypt();//encrypts the current file. } } Here is the section of my file creator that is failing to call this: FileWriter fWriter = null; BufferedWriter writer = null; try{ fWriter = new FileWriter("C:\\Users\\*******\\Desktop\\newtext"); writer = new BufferedWriter(fWriter); writer.write(Data); writer.close(); f.dispose(); FileEncryptor encr = new FileEncryptor(); //problem lies here. encr.encrypt //public void that does the encryption. new complete(); //different .java that is working fine.

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  • Bad_alloc exception when using new for a struct c++

    - by bsg
    Hi, I am writing a query processor which allocates large amounts of memory and tries to find matching documents. Whenever I find a match, I create a structure to hold two variables describing the document and add it to a priority queue. Since there is no way of knowing how many times I will do this, I tried creating my structs dynamically using new. When I pop a struct off the priority queue, the queue (STL priority queue implementation) is supposed to call the object's destructor. My struct code has no destructor, so I assume a default destructor is called in that case. However, the very first time that I try to create a DOC struct, I get the following error: Unhandled exception at 0x7c812afb in QueryProcessor.exe: Microsoft C++ exception: std::bad_alloc at memory location 0x0012f5dc.. I don't understand what's happening - have I used up so much memory that the heap is full? It doesn't seem likely. And it's not as if I've even used that pointer before. So: first of all, what am I doing that's causing the error, and secondly, will the following code work more than once? Do I need to have a separate pointer for each struct created, or can I re-use the same temporary pointer and assume that the queue will keep a pointer to each struct? Here is my code: struct DOC{ int docid; double rank; public: DOC() { docid = 0; rank = 0.0; } DOC(int num, double ranking) { docid = num; rank = ranking; } bool operator>( const DOC & d ) const { return rank > d.rank; } bool operator<( const DOC & d ) const { return rank < d.rank; } }; //a lot of processing goes on here; when a matching document is found, I do this: rank = calculateRanking(table, num); //if the heap is not full, create a DOC struct with the docid and rank and add it to the heap if(q.size() < 20) { doc = new DOC(num, rank); q.push(*doc); doc = NULL; } //if the heap is full, but the new rank is greater than the //smallest element in the min heap, remove the current smallest element //and add the new one to the heap else if(rank > q.top().rank) { q.pop(); cout << "pushing doc on to queue" << endl; doc = new DOC(num, rank); q.push(*doc); } Thank you very much, bsg.

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  • java bubblesort with acm dialog

    - by qzar
    Hi, the program gives following exception: Exception in thread "main" java.lang.NullPointerException at myclasses.BubbleSort.run(BubbleSort.java:42) at acm.program.Program.runHook(Program.java:1519) at acm.program.Program.startRun(Program.java:1508) at acm.program.Program.start(Program.java:729) at myclasses.BubbleSort.main(BubbleSort.java:49) what is wrong? thank you very much! package myclasses; import acm.program.DialogProgram; public class BubbleSort extends DialogProgram { int[] array; public int[] getArray() { return array; } public void setArray(int[] array) { this.array = array; } void swap(int firstPos, int secondPos) { int temp = array[firstPos]; array[firstPos] = array[secondPos]; array[secondPos] = temp; } public void bubblesort() { int i, j, k; for (i = 1; i < array.length; i++) { j = i; k = array[i]; while (j > 0 && array[j - 1] > k) { array[j] = array[j - 1]; --j; } array[j] = k; } } public void run() { BubbleSort a = new BubbleSort(); a.setArray(new int[] {1, 3, 5, 7, 6, 2}); a.bubblesort(); StringBuffer sb = new StringBuffer(a.array.length * 2); for (int i = 0; i < getArray().length; i++) sb.append(getArray()[i]).append(" "); println(sb); } public static void main(String[] args) { new BubbleSort().start(args); } }

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  • Problem with sending out variable to serial port using api JAVA

    - by sjaakensjon
    We are developing a java program for school. But we are experiencing problems with sending out a variable created by 3 sliders. The idea is that we have 3 sliders. One slider for every color. Red green and blue. The variable has to have a value between 0 and 255. Everytime the value of the slider changes is has to send a variable for the channel, that value is 1, 2 ,3. And after that it has to send the value of the slider through the serial port. Could you please help us out by creating an example program? Below is our code so far. Thanks in advance. Sjaak package main; import javax.swing.*; import javax.swing.event.*; import java.awt.*; import app.Com; import app.Parameters; public class menu{ JSlider sliderblauw; JLabel hoeveelblauw; JLabel blauw; JLabel rood; JSlider sliderrood; JLabel hoeveelrood; JLabel groen; JLabel hoeveelgroen; JSlider slidergroen; public menu(){ Frame venster = new JFrame("Color control"); JPanel blauwinstel = new JPanel(); ((JFrame) venster).setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); venster.setSize(500, 500); venster.setVisible(true); sliderblauw = new JSlider(JSlider.VERTICAL, 0, 255, 0); sliderblauw.addChangeListener(new veranderingblauw()); hoeveelblauw = new JLabel ("0"); blauwinstel.add(sliderblauw); blauwinstel.add(hoeveelblauw); venster.add(blauwinstel, BorderLayout.WEST); sliderblauw.setMajorTickSpacing(10); sliderblauw.setPaintTicks(true); JPanel roodinstel = new JPanel(); sliderrood = new JSlider(JSlider.VERTICAL, 0, 255, 0); sliderrood.addChangeListener(new veranderingrood()); hoeveelrood = new JLabel ("0"); roodinstel.add(sliderrood); roodinstel.add(hoeveelrood); venster.add(roodinstel, BorderLayout.EAST); sliderrood.setMajorTickSpacing(10); sliderrood.setPaintTicks(true); JPanel groeninstel = new JPanel(); slidergroen = new JSlider(JSlider.VERTICAL, 0, 255, 0); slidergroen.addChangeListener(new veranderinggroen()); hoeveelgroen = new JLabel ("0"); groeninstel.add(slidergroen); groeninstel.add(hoeveelgroen); venster.add(groeninstel, BorderLayout.CENTER); slidergroen.setMajorTickSpacing(10); slidergroen.setPaintTicks(true); } public class veranderingblauw implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = sliderblauw.getValue(); String waarde_blauw = Integer.toString(value); hoeveelblauw.setText(waarde_blauw); }} public class veranderingrood implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = sliderrood.getValue(); String waarde_rood = Integer.toString(value); hoeveelrood.setText(waarde_rood); }} public class veranderinggroen implements ChangeListener{ public void stateChanged(ChangeEvent ce){ int value = slidergroen.getValue(); String waarde_groen = Integer.toString(value); hoeveelgroen.setText(waarde_groen); }} public static void main( String[] args) { new menu(); } }

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  • Longer execution through Java shell than console?

    - by czuk
    I have a script in Python which do some computations. When I run this script in console it takes about 7 minutes to complete but when I run it thought Java shell it takes three times longer. I use following code to execute the script in Java: this.p = Runtime.getRuntime().exec("script.py --batch", envp); this.input = new BufferedReader(new InputStreamReader(p.getInputStream())); this.output = new BufferedWriter(new OutputStreamWriter(p.getOutputStream())); this.error = new BufferedReader(new InputStreamReader(p.getErrorStream())); Do you have any suggestion why the Python script runs three time longer in Java than in a console? update The computation goes as follow: Java sends data to the Python. Python reads the data. Python generates a decision tree --- this is a long operation. Python sends a confirmation that the tree is ready. Java receives the confirmation. Later there is a series of communications between Java and Python but it takes only several second.

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  • Java Class<T> static method forName() IncompatibleClassChangeError

    - by matt
    Hi, i have this code: private static Importable getRightInstance(String s) throws Exception { Class<? extends Importable> c = Class.forName(s).asSubclass(Importable.class); Importable i = c.newInstance(); return i; } which i can also write private static Importable getRightInstance(String s) throws Exception { Class<? extends Importable> c = (Class<? extends Importable>)Class.forName(s); Importable i = c.newInstance(); return i; } or private static Importable getRightInstance(String s) throws Exception { Class<?> c = Class.forName(s); Importable i = (Importable)c.newInstance(); return i; } where Importable is an interface and s is a string representing an implementing class. Well, in any case it gives the following: Exception in thread "main" java.lang.IncompatibleClassChangeError: class C1 has interface Importable as super class Here is the last snippet of the stack trace: at java.lang.Class.forName(Class.java:169) at Importer.getRightImportable(Importer.java:33) at Importer.importAll(Importer.java:44) at Test.main(Test.java:16) Now, class C1 actually implemens Importable and i totally don't understand why it complaints. Thanks in advance.

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  • Java constructor using generic types

    - by Beer Me
    I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method breweryMethod() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // breweryMethod() is an instance method // of Brewery, of which <T> is a subclass (right?) c.breweryMethod(); // "The method breweryMethod() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void brewerySubClassMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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  • Is app stability unusually hard with Java?

    - by wrp
    Java's extensive libraries and tool support are appealing, but I've never tried developing with it because most Java applications I've used have been extremely buggy. This has me puzzled, because I hear that Java is the dominant platform for enterprise development. Maybe it's fine for server-side stuff but not desktop applications. I'm not talking about things like the long compile/startup times or the random latencies due to garbage collection. This is about things just going wrong. Some of the most common problems I see are: corrupted icons corrupted fonts, in menus usually and editing areas sometimes inaccurate framing of GUI elements dialogs sometimes popping up blank Maybe the problems are mostly with Swing. I've rarely used a Java application long enough to find deeper issues. I can think of a few possible explanations for what I've experienced: It's possible to write stable apps with Java, just harder. Java apps are always buggy and enterprise users just put up with it. Server-side apps are fine because just Swing is buggy. I'm living under a curse and need the services of a good witchdoctor.

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  • Autocomplete for generic types in Eclipse

    - by AvrDragon
    "Refer to objects by their interfaces" is a good practise, as mentioned in Effective Java. So for example i prefer List<String> al = new ArrayList<String>(); over ArrayList<String> al = new ArrayList<String>(); in my code. One annoying thing is that if i type ArrayList<String> al = new and then hit Ctrl+Space in Eclipse i get ArrayList<String>() as propostal. But if i type List al = new and then hit Ctrl+Space i will get only propostal to define anonymous inner class, but not propostals such as new ArrayList<String>(), what is 99% the case, or for example new Vector<String>(). Is there any way to get the subclasses as propostals for generic types?

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  • Java constructor using generic types

    - by user37903
    I'm having a hard time wrapping my head around Java generic types. Here's a simple piece of code that in my mind should work, but I'm obviously doing something wrong. Eclipse reports this error in BreweryList.java: The method initBreweryFromObject() is undefined for the type <T> The idea is to fill a Vector with instances of objects that are a subclass of the Brewery class, so the invocation would be something like: BreweryList breweryList = new BreweryList(BrewerySubClass.class, list); BreweryList.java package com.beerme.test; import java.util.Vector; public class BreweryList<T extends Brewery> extends Vector<T> { public BreweryList(Class<T> c, Object[] j) { super(); for (int i = 0; i < j.length; i++) { T item = c.newInstance(); // initBreweryFromObject() is an instance method // of Brewery, of which <T> is a subclass (right?) c.initBreweryFromObject(); // "The method initBreweryFromObject() is undefined // for the type <T>" } } } Brewery.java package com.beerme.test; public class Brewery { public Brewery() { super(); } protected void breweryMethod() { } } BrewerySubClass.java package com.beerme.test; public class BrewerySubClass extends Brewery { public BrewerySubClass() { super(); } public void androidMethod() { } } I'm sure this is a complete-generics-noob question, but I'm stuck. Thanks for any tips!

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  • Java program using a class from a JAR file

    - by Myn
    Hi guys, I'll try to phrase this as best I can. I have a program which has an API-like functionality - it uses reflection to dynamically call methods from within a class. In this instance: Server.java public static void main(String[] args) { Class<?> clazz = Class.forName("DiHandler"); StHandler out = (StHandler) clazz; out.read(); DiHandler.java // implements StHandler import edu.ds.*; public void read() { Ds aType = new Ds(); aType = "134"; } So DiHandler has a method read() which can contain anything, it doesn't matter to Server.java after compile time. My problem is: DiHandler.java uses the class Ds from a JAR file. When I'm working on DiHandler.java in Eclipse (in a separate project from the project Server.java is in) I can add this JAR without a problem. But when I move DiHandler.class, after it's compiled, to be used by Server.class, how can it still use the JAR file? I hope this makes some sense, I suppose another way to phrase it would be how can I allow DiHandler to call on a class from the JAR without editing the classpath? Thanks very much in advance and sorry for any confusion or poor phrasing, I can only offer thanks and the customary offer of a pint for any assistance. M

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  • Java Equivalent of C++ .dll?

    - by Matt D
    So, I've been programming for a while now, but since I haven't worked on many larger, modular projects, I haven't come across this issue before. I know what a .dll is in C++, and how they are used. But every time I've seen similar things in Java, they've always been packaged with source code. For instance, what would I do if I wanted to give a Java library to someone else, but not expose the source code? Instead of the source, I would just give a library as well as a Javadoc, or something along those lines, with the public methods/functions, to another programmer who could then implement them in their own Java code. For instance, if I wanted to create a SAX parser that could be "borrowed" by another programmer, but (for some reason--can't think of one in this specific example lol) I don't want to expose my source. Maybe there's a login involved that I don't want exploited--I don't know. But what would be the Java way of doing this? With C++, .dll files make it much easier, but I have never run into a Java equivalent so far. (I'm pretty new to Java, and a pretty new "real-world" programmer, in general as well)

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  • How to connect SQLite with Java?

    - by Rajapandian
    Hi, I am using one simple code to access the SQLite database from Java application . My code is import java.sql.Connection; import java.sql.DriverManager; import java.sql.ResultSet; import java.sql.Statement; public class ConnectSQLite { public static void main(String[] args) { Connection connection = null; ResultSet resultSet = null; Statement statement = null; try { Class.forName("org.sqlite.JDBC"); connection = DriverManager.getConnection("jdbc:sqlite:D:\\testdb.db"); statement = connection.createStatement(); resultSet = statement .executeQuery("SELECT EMPNAME FROM EMPLOYEEDETAILS"); while (resultSet.next()) { System.out.println("EMPLOYEE NAME:" + resultSet.getString("EMPNAME")); } } catch (Exception e) { e.printStackTrace(); } finally { try { resultSet.close(); statement.close(); connection.close(); } catch (Exception e) { e.printStackTrace(); } } } } But this code gives one exception like java.lang.ClassNotFoundException: org.sqlite.JDBC Any body knows how to slove it,please help me.

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