Array of strings in Java NULL pointer exception

Question

I want to make an array of strings

I do not have a fixed size for it

As it must be initialized, I intialize it with null .. it give java null pointer exception ???

in another part of my code , I loop on the array to print its contents.. so how to get over this error without having a fixed size

   public static String[] Suggest(String query, File file) throws FileNotFoundException
{
    Scanner sc2 = new Scanner(file);
    LongestCommonSubsequence obj = new LongestCommonSubsequence();
    String result=null;
    String matchedList[]=null;
    int k=0;

    while (sc2.hasNextLine()) 
    {
        Scanner s2 = new Scanner(sc2.nextLine());
        while (s2.hasNext()) 
            {
            String s = s2.next();
            //System.out.println(s);
            result = obj.lcs(query, s);

                if(!result.equals("no match"))
                {matchedList[k].equals(result); k++;}

            }
        return matchedList;
    }
    return matchedList;
}

This code won't even compile. What are you trying to achieve here. — Tim Biegeleisen, Jul 02 '15 at 07:57
Arrays in java are always fixed size - if you need variable size use a `List` — piet.t, Jul 02 '15 at 07:58
You should use List instead of an array to avoid NullPointerExceptions during iteration. — sinclair, Jul 02 '15 at 07:58
@sinclair A list variable initialized to null would still throw a NPE. — xlecoustillier, Jul 02 '15 at 07:58
Of course, but you never initialize a List with null, you can initialize with new without having a fixed size — Pierre-Alexandre Moller, Jul 02 '15 at 07:59
1- read a filname from user 2- read a word from user 3- find the words matching the user's search word based on Longest common subsequence .. so if the result of LSC is not "no match".... put this word in the array — CodeX, Jul 02 '15 at 08:01
@X.L.Ant If you iterate over a List and check for `isEmpty()` there shouldn't be any NPEs. Principle point of my comment was to prefer List over array in this situation. — sinclair, Jul 02 '15 at 08:04
@X.L.Ant I initialized list with null .. same error..can you post a solution? — CodeX, Jul 02 '15 at 08:05
possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — xlecoustillier, Jul 02 '15 at 08:07

score 0 · Answer 1 · answered Jul 02 '15 at 08:52

If you don't know the size, List is always better.

To avoid NPE, you have to initialize your List like this :

List<String> matchedList = new ArrayList<String>();

ArrayList is a example, you can use all king of list you needed.

And to get your element instead of matchedList[index] you will have this :

macthedList.get(index);

So our code it will be like this :

public static String[] Suggest(String query, File file) throws FileNotFoundException
{
...
List<String> matchedList= new ArrayList<String>();
...

while (sc2.hasNextLine()) 
{
    Scanner s2 = new Scanner(sc2.nextLine());
    while (s2.hasNext()) 
    {
        ...
        if(!result.equals("no match")){
          //This line is strange. See explanation below
          matchedList.get(k).equals(result);
          k++;
         }
    }
    return matchedList;
}
return matchedList;
}

There is something strange in your code :

matchedList.get(k).equals(result);

When you do that, you compare both value and it will return true or false. It's possible that you want to add the value on your list, in this case you have to do it like this :

matchedList.add(result);

Array of strings in Java NULL pointer exception

1 Answers1