reading text file into constructor array (java)

Question

I have a textfile with some values.

textfile data

line1row1 line1row2 55
line2row1 line2row2 44
line3row1 line3row2 33

I have a data class where i have created a contructor. the data which goes into the array, i want read from the text file.

import java.io.*; 
import java.util.*;

class Data{
    public Data(String entry1, String entry2, int entry3){}
}   
public class readData {
    public static void main(String[] args) throws Exception{
    BufferedReader inFile = new BufferedReader (new FileReader ("scores.txt"));

    Data entrydata[] = new Data[3]; //create new constructor array
    for(int i = 0; i < entrydata.length; i++ ){
            entrydata[i] = inFile.readLine();
        }
    }
}

I get an error on "inFile.readLine()"... Cannot Convert from String to Data(where "Data" refers to class)

I can hardcode the data [as below] but want it to be read from the file instead

Data entrydata[] = new Data[3];
entrydata [0] = new Data("line1row1 ", "line1row2 ", 55);
entrydata [1] = new Data("line2row1 ", "line2row2 ", 44);
entrydata [2] = new Data("line3row1 ", "line3row2 ", 33);

The reason I want to do this, is so that I can access the informatin stored in the array.

Steve Claridge · Accepted Answer · 2011-11-05 21:40:35Z

2

inFile.readline() returns a string, which isn't a Data object and so you get the error message. You need to split the string you read from the file into an array and the use the array elements to create your data items. Something like:

String[] tmp = inFile.readline().split( " " );
entrydata[i] = new Data( tmp[0], tmp[1], Integer.parseInt( tmp[2] ) );

answered Nov 5, 2011 at 21:40

Steve Claridge

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2 Comments

user1031551 Over a year ago

Thank you, that worked once i fugured out how! Now I need to figure out why i am getting a nullpointerexception (i am using an array with many more indices than the initial 3, to allow me to add further values when required). It also seems to ignore the first line in my file, and only start reading the objects from line 2, but then throws the nullpointerexception

user1031551 Over a year ago

Found it: Data entrydata[] = new Data[3]; for (int i = 0; i < entrydata.length; i++ ){ entrydata[i] = new Data(inFile.readLine().split(" ")); When you have an array larger than the data being read, it seems that you should not use "i < entrydata.length" but rather the number of entries in your file it is reading such as 3. Then you dont get the nullpointerexception.

Akintayo Olusegun · Accepted Answer · 2011-11-05 22:11:46Z

1

I woud do something like this

class Data{
    String entry1, entry2;
    int entry3;
    public Data(String[] datas) throws NumberFormatException {
        entry1 = datas[0];
        entry2 = datas[1];
        entry3 = Integer.parseInt(datas[2]);
    }
}
    .
    .
    .
    .
Data entrydata[] = new Data[3]; //this is not a constructor
for(int i = 0; i < entrydata.length; i++ ){
    entrydata[i] = new Data(inFile.readLine().split(" ")); //this is the constructor
}

answered Nov 5, 2011 at 22:11

Akintayo Olusegun

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Comments

JB Nizet · Accepted Answer · 2011-11-05 21:41:17Z

0

How could the readLine method, which reads a line of text from the file, know how to transform the line into a Data instance? It doesn't read in your mind.

So you have to tell it how to transform the line into three components. You might use the String.split method to split the line at every space character, and the Integer.parseInt method to transform the third token into an integer.

Also, your code assumes that the file contains exactly 3 lines. If that's not necessarily the case, you should loop until the next line is null, and put each Data instance into a List<Data> rather than an array. The list will automatically grow in size, which an array can't do.

answered Nov 5, 2011 at 21:41

JB Nizet

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Comments

wannik · Accepted Answer · 2011-11-07 18:39:51Z

0

Your readData class does not have a constructor or a method. The code in line 11-15 needs to be in a method/constructor.

If the length each entry is fixed, you might try line.substring(...) instead of line.split(...).

The name of the class should be ReadData.

answered Nov 7, 2011 at 18:39

wannik

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Comments

Roma Khimani · Accepted Answer · 2014-09-10 10:14:40Z

0

This code will definetly work:

FileReader fr =new FileReader("src/FilePractice.txt");
BufferedReader in =new BufferedReader(fr);
String line;
        while((line = in.readLine()) != null){
            String[] arrray=line.split(",");
            RelationShip r=RelationShip.valueOf(arrray[2]);
            new Data(arrray[0],arrray[1],r,Integer.parseInt(arrray[3]));
            System.out.println(arrray[0]+arrray[1]+arrray[2]+arrray[3]);

answered Sep 10, 2014 at 10:14

Roma Khimani

1

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