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Thread: Please help with code. Null Pointer Exception

  1. #1
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    Post Please help with code. Null Pointer Exception

    Hello. I am having a problem with my code where I keep getting Null Pointer Exceptions and also I am having trouble with my file intake. This is my code minus the printlns at the end

    import java.io.*;
    import java.util.Scanner;
    public class P1 {
    	public static void main(String[] args){
    		int fileLinesCt=0, totalLinesCt=0;
    		int httpCt=0, httpsCt=0, ftpCt=0, otherSchemeCt=0;
    		int eduCt=0, orgCt=0, comCt=0, otherDomainCt=0;
    		Scanner scan = null;
    		String url = null, scheme = null, schemeSP = null, domain = null;
     
    		File file = new File("input");
            try {
                scan = new Scanner(file);
            }
            catch (FileNotFoundException e) {
                e.printStackTrace();
            }
    		Scanner scan2 = new Scanner(System.in);
    		while (!"end".equals(scan.next()) || (!"end".equals(scan2.next()))){
    			if (scan.hasNext() == true)
    				url = scan.nextLine();
    			String[] parts = url.split(":");
    			scheme = parts[0];
    			schemeSP = parts[1];
    			if ("http".equals(scheme))
    				httpCt++;
    			if ("https".equals(scheme))
    				httpsCt++;
    			if ("ftp".equals(scheme))
    				ftpCt++;
    			else otherSchemeCt++;
    			for (int j=0; j<schemeSP.length(); j++)
    				if (schemeSP.charAt(j) == '.')
    					domain = schemeSP.substring(j);
    			if ("edu".equals(domain))
    				eduCt++;
    			if ("org".equals(domain))
    				orgCt++;
    			if ("com".equals(domain))
    				comCt++;
    			else otherDomainCt++;
    			fileLinesCt++;
    			totalLinesCt++;
    		}

    Now what the basis of the assignment is is that i have to take files that include urls that will be automatically tested to my code and run through them counting the number of times different schemes appear (http,https) and count the number of times different domains appear(.com,.edu). Now I do not know what the names of these files will be and this seems to be a problem I am having. Also, Null Pointer Exception is appearing on line 19 which is the first line of the while loop. Also, a FileNotFound exception is appearing on line 13 whick is the one that says scan = new Scanner(file);.

    Any help would be great.


  2. #2
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    Default Re: Please help with code. Null Pointer Exception

    NullPointerExceptions are caused by:
    MyObject obj; // initialised to null
    obj.callSomeMethod();  // NPE
    What you need to do is track down what variable is still null (never assigned a value) and why. Then you can fix it yourself. The error message will tell you what line the NPE occurs on. Place a print statement before that and print out all variables to find out what is null.
    Improving the world one idiot at a time!

  3. The Following User Says Thank You to Junky For This Useful Post:

    JMBenoit18 (September 16th, 2013)

  4. #3
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    Default Re: Please help with code. Null Pointer Exception

    So i have now figured that out. Thank you. But another problem I am having now is that line 73 (schemeSP = parts[1] is giving me an ArrayIndexOutOfBounds exception. Any ideas why this is happening?

  5. #4
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    Default Re: Please help with code. Null Pointer Exception

    It would seem that the call to split is not working and is returning an array with a single value (the entire String) at index 0. Therefore index 1 does not exist. Print out parts[0] to confirm.
    Improving the world one idiot at a time!

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