Question

I’m trying to make a new thread for parsing xml from an rss feed. When I click run it says there are errors please correct them etc. I have 2 classes in my project. The other class has no errors and this class below has only warnings that a lot of the things in the try/catch statements may be uninitialized. I understand that and figured I should still be able to run the program anyways, I expect them to be initialized and if they’re not that’s fine I want to know about it. Is this really what’s going on or am I missing something? I thought it would compile if something may be uninitialized but its not certainly uninitialized.

public class RssParse extends Thread  {
    Thread th=new Thread() {
            public void run(){
              System.out.println("1");
              URL iotd;
            try {
                iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
            } catch (MalformedURLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("2");
            BufferedReader in;

                try {
                    in = new BufferedReader(new InputStreamReader(iotd.openStream()));
                } catch (IOException e1) {
                    // TODO Auto-generated catch block
                    e1.printStackTrace();
                }

            System.out.println("3");
            XmlPullParserFactory factory;
            try {
                factory = XmlPullParserFactory.newInstance();
            } catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }

            factory.setNamespaceAware(true);
            System.out.println("4");
            XmlPullParser xpp;
            try {
                xpp = factory.newPullParser();
            } catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("5");
            try {
                xpp.setInput(in);
            } catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println("6");

            int eventType;
            try {
                eventType = xpp.getEventType();
            } catch (XmlPullParserException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            System.out.println(eventType+"!!!!!!!!!!!!!!!!");
            while(eventType!=XmlPullParser.END_DOCUMENT){
                if(eventType==XmlPullParser.START_DOCUMENT){
                    System.out.println("start");
                }
            }

            try {
                in.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
            }//method
        };//thread

}//class

Answer 1

Look at this try/catch block for example :

    URL iotd;
    try {
        iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
    } catch (MalformedURLException e) {
        e.printStackTrace();
    }

If iotd = new URL("...") fails, iotd will remain uninitialized.

There are two ways to deal with this :

• Assign a default value to iotd, like : URL iotd = null; However, it’s bad here because if you use iotd later its value may be null and can throw a NullPointerException.

• Stop the execution of your function if something failed instead of just printing the stack trace. For example you can add a return statement in the catch block :

  URL iotd;
  try {
      iotd = new URL("http://www.nasa.gov/rss/image_of_the_day.rss");
  } catch (MalformedURLException e) {
      e.printStackTrace();
      return;
  }