Best way to read data from a file

Question

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Best way to read a text file

In Java I can open a text file like this:

BufferedReader reader = new BufferedReader(new FileReader("file.txt"));

My question is, how do you read from the following file? The first line is a number (830) representing number of words, and the following lines contain the words.

830  
cooking   
English  
weather  
.  
.

I want to read the words into a string array. But how do I read the data first?

score 4 · Answer 1 · answered Aug 16 '11 at 01:23

You're on the right track; I would treat the first line as a special case by parsing it as an integer (see Integer#parseInt(String)) then reading the words as individual lines:

BufferedReader reader = new BufferedReader(new FileReader("file.txt"));
String numLinesStr = reader.readLine();
if (numLinesStr == null) throw new Exception("invalid file format");
List<String> lines = new ArrayList<String>();
int numLines = Integer.parseInt(numLinesStr);
for (int i=0; i<numLines; i++) {
  lines.add(reader.readLine());
}

score 1 · Answer 2 · answered Aug 16 '11 at 01:27

Unless you have some special reason, it's not necessary to keep track of how many lines the file contain. Just use something like this:

BufferedReader reader = new BufferedReader(new FileReader("file.txt"));

String line;
while ((line = reader.readLine()) != null) {
    // ...
}

score 1 · Answer 3 · edited Feb 07 '18 at 19:36

1

If you're working with Java version greater than 1.5, you can also use the Scanner class:

Scanner sc = new Scanner(new File("someTextFile.txt"));
List<String> words = new ArrayList<String>();
int lines = sc.nextInt();

for(int i = 1; i <= lines; i++) {
    words.add(sc.nextLine());
}

String[] w = words.toArray(new String[]{});

edited Feb 07 '18 at 19:36

Peter Mortensen

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answered Aug 16 '11 at 04:22

Dragon8

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score 0 · Answer 4 · answered Aug 16 '11 at 01:29

Try the class java.io.BufferedReader, created on a java.io.FileReader. This object has the method readLine, which will read the next line from the file:

try
{
    java.io.BufferedReader in = 
        new java.io.BufferedReader(new java.io.FileReader("filename.txt"));

    String str;
    while((str = in.readLine()) != null)
    {
        ...
    }
 }
 catch(java.io.IOException ex)
 {
 }

Shawn · Answer 5 · 2011-08-16T01:57:15.353

You could use reflection and do this dynamically:

 public static void read() {

            try {
                BufferedReader reader = new BufferedReader(new FileReader(
                        "filename.txt"));

                String line = reader.readLine();

                while (line != null) {
                    if (Integer.class.isAssignableFrom(line.getClass())) {
                        int number = Integer.parseInt(line);
                        System.out.println(number);
                    } else {
                        String word = line;
                        System.out.println(word);
                    }

                    line = reader.readLine();
                }
            } catch (FileNotFoundException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }

        }

Best way to read data from a file

5 Answers5