File Handling - Reading from the beginning again

Question

I need to create an array of objects to save the records from files. I don't know about the size of an array. For that I have to find the number of lines in a file first. Using the number of lines, size of an array can be determined. Now I need to read the file again from the beginning to store records from the file in array object. This is where I am struggling. I don't know how to implement in order to read the file again from the beginning. Please advise.

/**
     * Loads the game records from a text file.
     * A GameRecord array is constructed to store all the game records.
     * The size of the GameRecord array should be the same as the number of non-empty records in the text file.
     * The GameRecord array contains no null/empty entries.
     * 
     * @param reader    The java.io.Reader object that points to the text file to be read.
     * @return  A GameRecord array containing all the game records read from the text file.
     */


    public GameRecord[] loadGameRecord(java.io.Reader reader) {
        // write your code after this line
        String[] parts;
        GameRecord[] gameRecord = null;
        FileReader fileReader = (FileReader) reader;
        java.io.BufferedReader bufferedReader = new java.io.BufferedReader(fileReader);
        try {
            int linenumber = 0;
            String sCurrentLine;
            while ((sCurrentLine = bufferedReader.readLine()) != null){
                System.out.println(sCurrentLine);
                linenumber++;
            }
            gameRecord = new GameRecord[linenumber]; //creating a space for total no Of lines

            //How to read the file from the beginning again, and why I am getting bufferedReader.readLine()) as null
            bufferedReader = new java.io.BufferedReader(fileReader); 
            while ((sCurrentLine = bufferedReader.readLine()) != null){
                System.out.println(sCurrentLine);
                parts = sCurrentLine.split("\t");
                    gameRecord[i] = new GameRecord(parts[0], Integer.parseInt(parts[1]),Integer.parseInt(parts[2]));
            }

        }catch (IOException exe){
            System.err.println("IOException: " + exe.getMessage());
            exe.printStackTrace();
        }finally{
            try {
                if (bufferedReader!=null)
                    bufferedReader.close();
                if (fileReader!=null)
                    fileReader.close();
            }catch(IOException exe) {
                System.err.println("IOException: " + exe.getMessage());
            }           
        }
        return gameRecord; 
    }

Note: I will get the reference to a file as an argument. Reader class has been used. Can I use this reference for FileInputStream?

FileInputStream derived from Reader class? Reference to the file will be sent in an argument. — ahairshi, May 28 '15 at 08:05

score 3 · Accepted Answer · edited May 23 '17 at 11:44

3

Your current approach is very limiting because you are using an array which by definition has to be defined to have a fixed size. A better approach would be to use an ArrayList of GameRecord objects. With this approach, you can simply make one single pass through the file and add elements to the ArrayList as necessary.

Sample code:

List<GameRecord> grList = new ArrayList<GameRecord>();
bufferedReader = new java.io.BufferedReader(fileReader); 
while ((sCurrentLine = bufferedReader.readLine()) != null){
    parts = sCurrentLine.split("\t");
    GameRecord gameRecord = new GameRecord(parts[0],
                                           Integer.parseInt(parts[1]),
                                           Integer.parseInt(parts[2]));
    grList.add(gameRecord);  // add the GameRecord object to the ArrayList
                             // and let the JVM worry about sizing problems
}

// finally, convert the ArrayList to an array
GameRecord[] grArray = new String[grList.size()];
grArray = grList.toArray(grArray);

If you must reset the BufferedReader then have a look at this SO article which discusses this.

edited May 23 '17 at 11:44

Community

1
1

answered May 28 '15 at 07:59

Tim Biegeleisen

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Nope, I need to return an array of objects as per the question – ahairshi May 28 '15 at 08:01
1

we can convert Arraylist to array by using toArray() method. after getting array from list simply return that array. – Anil Reddy Yarragonda May 28 '15 at 08:03
Updated my answer to return an array. Using an array to read the file is _not_ the best way to go here. – Tim Biegeleisen May 28 '15 at 08:03
Yes, I implemented like this only. just wanted to know how the file can be read again using BufferedReader. – ahairshi May 28 '15 at 08:12
You don't need to read again if you use my solution. You can always close underlying file and then reopen it. – Tim Biegeleisen May 28 '15 at 08:20
Think we should remove for (int i=0; i – ahairshi May 28 '15 at 08:22

score 0 · Answer 2 · answered May 28 '15 at 08:01

0

if you used org.apache.commons.io.IOUtils, you could employ readLines method. as long as your file never contains "Too Many" records. this method returns a List which is easy to convert to array of Strings

answered May 28 '15 at 08:01

Hector

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I can't use third party APIs – ahairshi May 28 '15 at 08:06
then write your own java code to read complete file into ArrayList then convert ArrayList to String array. you only read file once and get array as result – Hector May 28 '15 at 08:08

File Handling - Reading from the beginning again

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