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Thread: Exception in thread "main" java.lang.NullPointerException

  1. #1
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    Question Exception in thread "main" java.lang.NullPointerException

    Hello, im new in this forum and programming in java, and i have a problem:
    at school we are programming this code to initialize the webcam and show it on the screen, but it doesn´t work :C this is a code that did run in another computer, but i cant see what's wrong with it . My webcam does work good, and the driver is already installed. Hope you can help me, im a noob u.u. Here is the code:

    package webcam;

    import java.awt.BorderLayout;
    import javax.media.CaptureDeviceInfo;
    import javax.media.CaptureDeviceManager;
    import javax.media.Manager;
    import javax.media.MediaLocator;
    import javax.media.Player;
    import javax.media.Processor;
    import javax.swing.JFrame;



    public class Webcam extends JFrame {

    private static Player player;
    private MediaLocator localizador;
    private Processor p;
    private CaptureDeviceInfo dispositivo=null;
    private static String source="vfw:Microsoft WDM Image Capture (Win32):0";

    public Webcam(){
    setLayout(new BorderLayout());
    setSize(500,400);
    setLocationRelativeTo(null);
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("Camara Web");
    player=null;
    localizador=null;
    dispositivo=CaptureDeviceManager.getDevice(source) ;
    localizador=dispositivo.getLocator();
    iniciarCaptura();
    }

    private void iniciarCaptura(){
    try{
    player=Manager.createRealizedPlayer(localizador);
    player.start();
    if(player.getVisualComponent()!=null){
    add(player.getVisualComponent(), BorderLayout.CENTER);
    }
    }
    catch(Exception e){
    System.err.println(e.toString());
    }
    }

    public static void main(String[] args) {
    Webcam camara=new Webcam();
    Webcam.setDefaultLookAndFeelDecorated(true);
    camara.setVisible(true);
    }
    }


    //THE ERROR IS THE NEXT ONE
    Exception in thread "main" java.lang.NullPointerException
    at webcam.Webcam.<init>(Webcam.java:35)
    at webcam.Webcam.main(Webcam.java:53)
    Java Result: 1

    please help! :C


  2. #2
    Super Moderator Norm's Avatar
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    Default Re: Exception in thread "main" java.lang.NullPointerException

    Please edit your post and wrap your code with code tags:
    [code=java]
    <YOUR CODE HERE>
    [/code]
    to get highlighting and preserve formatting.
    If you don't understand my answer, don't ignore it, ask a question.

  3. #3
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    Default Re: Exception in thread "main" java.lang.NullPointerException

    You are correct to assume "CaptureDeviceManager.getDevice(source);" is resulting in null.
    Based on the api for that method (JMF 2.0 API (03/10/01): Class CaptureDeviceManager "Returns null if the specified device could not be found."
    So the question now is why can the device not be found?
    I don't have the time at the moment to do the google searching for you, but the next step in debugging would be to get java to retrieve a list of devices attached to your computer. There is probably some topics out there regarding this if you search around (or perhaps someone else on the forum already knows). Get the list, and then loop through the list and print out the source names. This could be something as simple as you are using the wrong source name in the getDevice() method. But, first we want to make sure java recognizes a webcam is attached in the first place.
    NOTE TO NEW PEOPLE LOOKING FOR HELP ON FORUM:

    When asking for help, please follow these guidelines to receive better and more prompt help:
    1. Put your code in Java Tags. To do this, put [highlight=java] before your code and [/highlight] after your code.
    2. Give full details of errors and provide us with as much information about the situation as possible.
    3. Give us an example of what the output should look like when done correctly.

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