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Thread: Getting Null Pointer Exception in runtime

  1. #1
    Junior Member RoadRunner's Avatar
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    Question Getting Null Pointer Exception in runtime

    Please can sum1 help me with the above error in this code:
    import java.util.*; //required for List and ArrayList
    import java.io.*; //required for IOException
     
    public class TextFileTester
    {
    public static void main(String[] args)
    	{
    	char choice;
    	//create an object of type list to store the cars in
    	List<Car> carList = new ArrayList<Car>();
    	//read the list from file when program starts
    	readList(carList);
     
    		//menu options
    		do
    			{
    			System.out.println("\nText File Tester");
    			System.out.println("1. Add a car");
    			System.out.println("2. Remove a car");
    			System.out.println("3. List all cars");
    			System.out.println("4. Quit\n");
    			choice = KBInput.readChar();
    			System.out.println();
     
    			switch(choice)
    				{
    				case '1': addCar(carList);break;
    				case '2': removeCar(carList);break;
    				case '3': listAll(carList);break;
    				case '4': writeList(carList);break;
    				default: System.out.println("Choose an option between 1-4");
    				}
    			}
    		while(choice != '4');
    	}
     
    //method for adding a new car to the system
    private static void addCar(List<Car> carListIn)
    	{
    	String tempReg;
    	String tempMake;
    	double tempPrice;
     
    	System.out.println("Enter the veichle reg");
    	tempReg = KBInput.readString();
    	System.out.println("Enter the veichle make");
    	tempMake = KBInput.readString();
    	System.out.println("Enter veichle price");
    	tempPrice = KBInput.readDouble();
     
    	carListIn.add(new Car(tempReg, tempMake, tempPrice));
    	}
     
    //method for removing a car from the list
    private static void removeCar(List<Car> carListIn)
    	{
    	int pos;
    	System.out.println("Enter the position of the car to be removed");
    	pos = KBInput.readInt();
    	carListIn.remove(pos -1);
    	}
     
     
    //method for show all the cars in the list
    private static void listAll(List<Car> carListIn)
    	{
    		for(Car item: carListIn)
    		{
    			System.out.println(item.getRegistration() + ""
    			+ item.getMake() + "" + item.getPrice());
    		}
    	}
     
    //method for writing car list to file
    private static void writeList(List<Car> carListIn)
    	{
    	try
    		{
    		//create a file writer
    		FileWriter carFile = new FileWriter("Car.txt");
    		//create a print writer
    		PrintWriter carWriter = new PrintWriter(carFile);
    		for(Car item: carListIn)
    			{
    			carWriter.println(item.getRegistration());
    			carWriter.println(item.getMake());
    			carWriter.println(item.getPrice());
    			}
    		carWriter.close();
    		}
     
    		//handle the exceptions thrown up by the file writer
    			catch(IOException e)	
    				{
    				System.out.println("There was a problem writing the file");
    				}
    	}
     
    //method for reading the car file
    private static void readList(List<Car> carListIn)
    	{
    	String tempReg;
    	String tempMake;
    	String tempStringPrice;
    	double tempPrice;
     
    		try
    			{
    			//create a file reader
    			FileReader carFile = new FileReader("Car.txt");
    			//create a buffer for reader
    			BufferedReader carStream = new BufferedReader(carFile);
    			tempReg = carStream.readLine();
    			while (tempReg != null);
    				{
    				tempMake = carStream.readLine();
    				tempStringPrice = carStream.readLine();
    				// converting price from text to double
    				tempPrice = Double.parseDouble(tempStringPrice);
    				carListIn.add
    								(new Car(tempReg, tempMake, tempPrice));
    								tempReg = carStream.readLine();
    				}
    				carStream.close();
     
    			}
    			catch (FileNotFoundException e)
    				{
    				System.out.println("File could not be found");
    				}
     
    			catch (IOException e)
    				{
    				System.out.println("There was a problem reading the file");
    				}
    	}
    }
    The error:


    ----jGRASP exec: java TextFileTester

    Exception in thread "main" java.lang.NullPointerException
    at sun.misc.FloatingDecimal.readJavaFormatString(Floa tingDecimal.java:991)
    at java.lang.Double.parseDouble(Double.java:510)
    at TextFileTester.readList(TextFileTester.java:119)
    at TextFileTester.main(TextFileTester.java:12)

    ----jGRASP wedge2: exit code for process is 1.
    ----jGRASP: operation complete.

    from another forum i believe the variable tempStringPrice has a null value but i'm not sure what to set it to. Any help would be much appreciated
    Last edited by RoadRunner; April 26th, 2009 at 09:24 AM.


  2. #2
    Senile Half-Wit Freaky Chris's Avatar
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    Default Re: Null Pointer Exception runtime error

    Looks to me like you are trying to assign something within the file to it, but inactualy fact you are not assigning anything to it. Thus when you try to use it later (as you never initialised the String) it is throwing a null pointer exception

    Chris

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