Reading data into array from file

**r035198x** · Jan 9 '07, 06:28 AM

Originally posted by SkyGenius

Hello, I am a new Java learner. I would like to develop one model by using Java. In that model, there are many files to read. I want to write a method in Java to read a file and store the data in array(s). Later, I just only call that method to read other files. Would you please help me to write a code to read the data in the following formats:

First format (for example, separated by lines): store one column of the data in one array

11.1
22.2
33.3
...

Second format (for example, separated by spaces): store one column of the data in one array, so there are three arrays

1.1 11.1 111.1
2.2 22.2 222.2
3.3 33.3 333.3
... ... ...

Do you want to use one method to read both types of files?
Store the values in ArrayList rather than an Array so you don't have to find the number of lines in the files first.

Code:

 
public static ArrayList readFile(String fileName) {
  String line = "";
  ArrayList data = new ArrayList();//consider using ArrayList<int>
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);//Can also use a Scanner to read the file
   while((line = br.readLine()) != null) {
	
	data.add(line);
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }

For the second file you can make an ArrayList of ArrayList if you want to use the same method or an array of ArrayLists

**SkyGenius** · Jan 9 '07, 06:44 AM

Thanks for your help and comments. If possible, I would like to use two different methods to read the two different formats of the data files.

**r035198x** · Jan 9 '07, 06:53 AM

Originally posted by SkyGenius

Thanks for your help and comments. If possible, I would like to use two different methods to read the two different formats of the data files.

You could write the second one along the lines of

Code:

 
public static ArrayList[] readFile2(String fileName) {
  String line = "";
  ArrayList[] data = new ArrayList[3];//consider using ArrayList<int>
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);//Can also use a Scanner to read the file
   while((line = br.readLine()) != null) {
	String[] theline = line.split(" ");
	data[0].add(theline[0]);
	data[1].add(theline[1]);
	data[2].add(theline[2]);
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }

**SkyGenius** · Jan 9 '07, 07:43 AM

Could you make it in a complete class that is ready to run? For example, there is two files for the first format (so there are two arrays) and one file for second format (so there are three arrays). I would like to get those arrays in double type and it is ready to use for computation. Then I would like to write the two arrays from the first format to one file with two columns (first column for first array and second column for second array) . The arrays from the second format are written in two files. First file is for the first array and second file is for the three arrays (I would like to reproduce the second format file).

**r035198x** · Jan 9 '07, 08:08 AM

Originally posted by SkyGenius

Could you make it in a complete class that is ready to run? For example, there is two files for the first format (so there are two arrays) and one file for second format (so there are three arrays). I would like to get those arrays in double type and it is ready to use for computation. Then I would like to write the two arrays from the first format to one file with two columns (first column for first array and second column for second array) . The arrays from the second format are written in two files. First file is for the first array and second file is for the three arrays (I would like to reproduce the second format file).

Sorry I had gone out for a while.

Have a go at it first and post some code then I can see if you need help

Code:

 
import java.io.*;
import java.util.*;
public class ReadFile {
 public static void main(String args[]) {
  // You put your logic here
 }
 public static ArrayList[] readFile2(String fileName) {
  String line = "";
  ArrayList[] data = new ArrayList[3];
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
	String[] theline = line.split(" ");
	data[0].add(Double.parseDouble(theline[0]));
	data[1].add(Double.parseDouble(theline[1]));
	data[2].add(Double.parseDouble(theline[2]));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
 public static ArrayList<Double> readFile(String fileName) {
  String line = "";
  ArrayList<Double> data = new ArrayList<Double>();
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
	data.add(Double.parseDouble(line));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
}

**SkyGenius** · Jan 9 '07, 09:18 AM

Please help to fix this code.

Code:

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

public class ReadingFile {

public static void main(String args[]) {
	// You put your logic here
	int i,j;
	int count1,count2;		// number of the array elements
	
	int maxSize1 = 100;		// max number of array elements
	double[] dataArray1 = new double[maxSize1];
	double[] dataArray2 = new double[maxSize1];
	
	int maxSize2 = 50;
	double[] dataArray3 = new double[maxSize2];
	double[] dataArray4 = new double[maxSize2];
	double[] dataArray5 = new double[maxSize2];
	
	String fn1 = "file1.txt";
	String fn2 = "file2.txt";
	String fn3 = "file3.txt";
	/* first format: file1.txt and file2.txt
	   11.1
	   22.2
	   33.3
	   ...
	   
	   second format: file3.txt
	   1.1	11.1	111.1
	   2.2	22.2	222.2
	   3.3	33.3	333.3
	   ...	...		...
	   
	 */
	
	
	dataArray1 = readFile(fn1);	// I want to store the data from the first file
	dataArray2 = readFile(fn2);	// I want to store the data from the second file
		
	dataArray3 = readFile(fn3);	// I want to store the data of first colunm of the third file
	dataArray4 = readFile(fn3);	// I want to store the data of second colunm of the third file
	dataArray5 = readFile(fn3);	// I want to store the data of third colunm of the third file
	
	// I want to write the data that I read to a file
	FileWriter fout1 = new FileWriter("output1.txt");
	FileWriter fout2 = new FileWriter("output2.txt");
	
	for (i=0; (i<count1); i++){
		fout1.write(dataArray1[i]+" "+dataArray2[i]);	// I want to write to a file with two colonms
		
	}
	fout1.close();
	
	for (j=0; (j<count2); j++){
		fout2.write(dataArray3[j]+" "+dataArray4[j]+" "+dataArray4[j]);	// I want to write to reproduce the third file
		
	}
	fout2.close();
		
}
// I want to get count2(number of elements in each array) 
public static ArrayList[] readFile2(String fileName) {
  String line = "";
  ArrayList[] data = new ArrayList[3];
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
	String[] theline = line.split(" ");
	data[0].add(Double.parseDouble(theline[0]));
	data[1].add(Double.parseDouble(theline[1]));
	data[2].add(Double.parseDouble(theline[2]));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
//I want to get count1(number of elements of the array) 
 public static ArrayList<Double> readFile(String fileName) {
  String line = "";
  ArrayList<Double> data = new ArrayList<Double>();
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
	data.add(Double.parseDouble(line));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
}

**r035198x** · Jan 9 '07, 10:07 AM

Code:

 
import java.io.*;
import java.util.*; 
public class ReadingFile1 {

public static void main(String args[]) {
 // You put your logic here

 //Simply use ArrayList.size()
 //int i,j;
 //int count1,count2;  // number of the array elements

 //int maxSize1 = 100;  not neccessary

 //The methods are returning ArrayLists not arrays
 ArrayList<Double> dataArray1 = new ArrayList<Double>();
 ArrayList<Double> dataArray2 = new ArrayList<Double>();

 //only one array is required here
 ArrayList[] dataArray3 = new ArrayList[3];


 //int maxSize2 = 50;
 //double[] dataArray3 = new double[maxSize2];
 //double[] dataArray4 = new double[maxSize2];
 //double[] dataArray5 = new double[maxSize2];

 String fn1 = "file1.txt";
 String fn2 = "file2.txt";
 String fn3 = "file3.txt";
 /* first format: file1.txt and file2.txt
	11.1
	22.2
	33.3
	...

	second format: file3.txt
	1.1 11.1 111.1
	2.2 22.2 222.2
	3.3 33.3 333.3
	... ...  ...

  */


 dataArray1 = readFile(fn1); // I want to store the data from the first file
 dataArray2 = readFile(fn2); // I want to store the data from the second file
 // call the other method here
 dataArray3 = readFile2(fn3);


 //dataArray3 = readFile(fn3); // I want to store the data of first colunm of the third file
 //dataArray4 = readFile(fn3); // I want to store the data of second colunm of the third file
 //dataArray5 = readFile(fn3); // I want to store the data of third colunm of the third file

 // I want to write the data that I read to a file
 //You must handle the possible IOEeceptions
 try {
  FileWriter fout1 = new FileWriter("output1.txt");
  FileWriter fout2 = new FileWriter("output2.txt");
  for (int i = 0; i < dataArray1.size(); i++){
   fout1.write(dataArray1.get(i) + " " + dataArray2.get(i)); // I want to write to a file with two colonms
  }
  fout1.close();
 }
 catch(IOException iO) {
  iO.printStackTrace();
 }

 //Make sure the first one is working first
 //for (j=0; (j<count2); j++){
 // fout2.write(dataArray3[j]+" "+dataArray4[j]+" "+dataArray4[j]); // I want to write to reproduce the third file

 //}
 //fout2.close();

}
// I want to get count2(number of elements in each array)
public static ArrayList[] readFile2(String fileName) {
  String line = "";
  ArrayList[] data = new ArrayList[3];
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
 String[] theline = line.split(" ");
 data[0].add(Double.parseDouble(theline[0]));
 data[1].add(Double.parseDouble(theline[1]));
 data[2].add(Double.parseDouble(theline[2]));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
//I want to get count1(number of elements of the array)
 public static ArrayList<Double> readFile(String fileName) {
  String line = "";
  ArrayList<Double> data = new ArrayList<Double>();
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
 data.add(Double.parseDouble(line));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }
}

Have a look at the corrections and try and see if it works.
If there's any line you don't ubderstand there you might as well ask

**SkyGenius** · Jan 10 '07, 07:00 AM

Thanks so much for your help. I can successfully run the first method (readFile). But I still cannot run the second method (readFile2). It seems there are problems in declaration of dataArray3, calling method readFile2 and in the method itself.

**r035198x** · Jan 10 '07, 07:25 AM

Originally posted by SkyGenius

Thanks so much for your help. I can successfully run the first method (readFile). But I still cannot run the second method (readFile2). It seems there are problems in declaration of dataArray3, calling method readFile2 and in the method itself.

You'll have to be more specific. What problems are these compile time errors?

**SkyGenius** · Jan 10 '07, 07:31 AM

It shows this in console:
Exception in thread "main" java.lang.NullP ointerException
at fileReading.rea dFile2(fileRead ing.java:95)
at fileReading.mai n(fileReading.j ava:49)

**r035198x** · Jan 10 '07, 07:49 AM

Originally posted by SkyGenius

It shows this in console:
Exception in thread "main" java.lang.NullP ointerException
at fileReading.rea dFile2(fileRead ing.java:95)
at fileReading.mai n(fileReading.j ava:49)

Yep I had not initialised the array elements. Change the method to

Code:

 
public static ArrayList[] readFile2(String fileName) {
  String line = "";
  ArrayList[] data = new ArrayList[3];
  for(int i = 0; i < 3; i++) {
   data[i] = new ArrayList<Double>();
  }
  try {
   FileReader fr = new FileReader(fileName);
   BufferedReader br = new BufferedReader(fr);
   while((line = br.readLine()) != null) {
 String[] theline = line.split(" ");
 data[0].add(Double.parseDouble(theline[0]));
 data[1].add(Double.parseDouble(theline[1]));
 data[2].add(Double.parseDouble(theline[2]));
   }
  }
  catch(FileNotFoundException fN) {
   fN.printStackTrace();
  }
  catch(IOException e) {
   System.out.println(e);
  }
  return data;
 }

and test it.

May I add that you could have realised that yourself.

**SkyGenius** · Jan 10 '07, 02:16 PM

Thanks so much. It is running!

**r035198x** · Jan 10 '07, 03:03 PM

Originally posted by SkyGenius

Thanks so much. It is running!

Anytime Sky.

**SkyGenius** · Jan 11 '07, 06:10 AM

I can run the class. But when I use "space delimited format" for an input file, I could not write all read data to a file. The read data are displayed normally when I write it to the console.

Code:

for (int i = 0; i < inWL[0].size(); i++) {
	System.out.println(inWL[0].get(i) + " " + inWL[1].get(i));
	fout1.write(inWL[0].get(i) + " " + inWL[1].get(i) + "\n");
}

By the way, how could I modify my code to read a file with "tab delimited format"?

Code:

public static ArrayList[] readFile2(String fileName) {
	       / * File Structure:
		 * 	1.1 11.1
		 * 	2.2 22.2
		 *  3.3 33.3
		 * 	... ... 
		 */	
			String line = " ";
			ArrayList[] data = new ArrayList[2];
			
			//for(int i = 0; i < 2; i++) {
			data[0] = new ArrayList<String>();
			data[1] = new ArrayList<Double>();
			//}
			
			try {
				FileReader fr = new FileReader(fileName);
				BufferedReader br = new BufferedReader(fr);
				while((line = br.readLine()) != null) {
					String[] theline = line.split(" ");
					data[0].add(theline[0]);
					data[1].add(Double.parseDouble(theline[1]));
					
					//System.out.println(data[0] + "   " + data[1]);
				}
			}
			catch(FileNotFoundException fN) {
				fN.printStackTrace();
			}
			
			catch(IOException e) {
				System.out.println(e);
			}
			
			return data;

		} //end readFile2 method

Reading data into array from file

Reading data into array from file

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