CODEWITHSUNDEEP
javasorting
dk1
dk1

Reputation: 97

NullPointerException using java.util.Arrays.sort()

This program reads the lines of an input file and stores them into the array words. Then each element in words[] is put into a character array and sorted alphabetically. Each sorted character array is assigned to a string and those strings populate another array sortedWords. I need to sort the elements in the sortedWords array. I get a NullPointerException when I use Arrays.sort(sortedWords).

public static void main(String[] args) throws FileNotFoundException {
    Scanner scanner = new Scanner(System.in);
    System.out.print("Enter a file name: ");
    System.out.flush();

    String filename = scanner.nextLine();
    File file = new File(filename);

    String[] words = new String[10];
    String[] sortedWords = new String[10];

    try {   
        FileReader fr = new FileReader(file);
        BufferedReader br = new BufferedReader(fr);

        String line = br.readLine();
        int i = 0;

        while(line != null) {
            words[i] = line.toString();    // assigns lines into the array
            line = br.readLine();    // this will eventually set line to null, terminating the loop

            String signature = words[i];                        
            char[] characters = signature.toCharArray();        
            Arrays.sort(characters);
            String sorted = new String(characters);               

            sortedWords[i] = sorted;    // assigns each signature into the array
            sortedWords[i] = sortedWords[i].replaceAll("[^a-zA-Z]", "").toLowerCase();    // removes non-alphabetic chars and makes lowercase
            Arrays.sort(sortedWords); 

            System.out.println(words[i] + " " + sortedWords[i]);
            i++;
        }     
    } 

    catch(IOException e) {
        System.out.println(e);
    }
}

Upvotes: 1

Views: 11808

Answers (1)

cyon
cyon

Reputation: 9538

You should take the sort out of the while loop.

int i = 0;
while(line != null) {
   ...
   i++;
}
Arrays.sort(sortedWords, 0, i);

The problem is that you call sort before you finished populating the sortedWords array. The array therefore still contains null strings and these cause the NullPointerException.

Upvotes: 3

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