Null Errors in the output after Reading file

Question

I am doing this program and I keep getting "null" error at the end of output when I print as you see in the code. It does read file fine, but at the end, it adds so many null. Any guidance will be appreciated! Here 's what I tried so far.

public static void main(String[] args) throws Exception
{
    Stack nifo=new Stack();
    FileReader file = new FileReader("infix.dat");
    try (BufferedReader br = new BufferedReader(file)) {
        String [] words = new String[50];
        String text="";
        int ctrl = 0;
        String Line =br.readLine();
        while (Line!= null)
            {
            words[ctrl]= Line;
            Line = br.readLine();
            ctrl = ctrl + 1;
            }//end of while loop


            for (int i = 0; i < words.length; i++)
             {
            System.out.println(words[i]);
             }
            file.close();
        } catch (IOException e) {
        e.printStackTrace();
    }//end of catch

}//end of main class

and my output is this below. As you see null is being printed at the end after I read my file.

 5 * 6 + 4
 3 - 2 + 
 ( 3 * 4 - (2 + 5)) * 4 / 2
 10 + 6 * 11 -(3 * 2 + 14) / 2
  2 * (12 + (3 + 5 ) * 2
   null
   null
   null
   null
   more nulls after that.

Thank you!

That's not an error, that's all the empty space in your array. — azurefrog
– azurefrog, Commented Feb 20, 2017 at 2:25

nhouser9 · Accepted Answer · 2017-02-20 02:30:37Z

1

You declare a fixed size array:

String[] words = new String[50];

Then you store some values in it, and then you print each element:

for (int i = 0; i < words.length; i++) {
    System.out.println(words[i]);
}

All of the elements that you didn't use are null. So if your file has 6 lines it will print those 6 lines and then 44 nulls, since you have not put anything in the other 44 slots of your array. I suggest you use a different data structure, like a list. This will allow you to store only the number of values that you need.

Try this:

public static void main(String[] args) throws Exception
{
    Stack nifo=new Stack();
    FileReader file = new FileReader("infix.dat");
    try (BufferedReader br = new BufferedReader(file)) {
        List<String> words = new LinkedList<>(); //replaced your array with a list
        String text="";
        String Line =br.readLine();
        while (Line!= null)
            {
            words.add(Line);
            Line = br.readLine();
            }//end of while loop

            for (String word : words)
             {
            System.out.println(word);
             }
            file.close();
        } catch (IOException e) {
        e.printStackTrace();
    }//end of catch

}//end of main class

answered Feb 20, 2017 at 2:30

nhouser9

6,7803 gold badges23 silver badges43 bronze badges

Sign up to request clarification or add additional context in comments.

2 Comments

mike Over a year ago

Thank you so much and thanks for the tip for linked list!!

nhouser9 Over a year ago

@mike happy to help! please remember to upvote and accept the answer if this solved your issue =]

ShayHaned · Accepted Answer · 2017-02-20 02:35:55Z

0

Since you are not sure of the Array size and if you want to stick to using arrays then the following might fix your problem

        for (int i = 0; i < words.length && words[i] != null; i++)
         {
            System.out.println(words[i]);
         }
        file.close();

Just make sure that your loop does not process null values for any index in words array. Because the indices that were never populated in the array were initialized to null when you declared a fix sized array

answered Feb 20, 2017 at 2:35

ShayHaned

3583 silver badges8 bronze badges

2 Comments

mike Over a year ago

Thanks for the input and quick answer.

ShayHaned Over a year ago

Hopefully that helped you, because I was not interested in replacing your array with some other data structure. But still the other answer is worth trying if you are looking for diversity :)

Collectives™ on Stack Overflow

Null Errors in the output after Reading file

2 Answers 2

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

2 Answers 2

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related