How to read in text files?

[conafam]

Hi,

I need to be able to create a very simple Java program (not javascript) which reads in a text file and then outputs it's contents to the screen. Although it sounds very simple I am an extreme beginner and was looking for some help.

The code I have just now is:

public class Tutorial1{
    
    private float[] data = new float[2000];

    //constructor
    public Tutorial1(){}

    /**
     *readData
     *input: String filename
     *store the values of the third column of numbers of the data file into the member array: data
     */
    public void readData(String filename){
	...
    }
    
    //entry point
    public static void main(String args[]){
	Tutorial1 tut1 = new Tutorial1();

	//read data
	tut1.readData("data.txt");
	//print out content of data
	....
	    }
}

Where the "...." are I need to complete my own code but I have no idea. Can someone help?

Much appreciated

[smeagol]

Here's an example of how to read in the contents of a text file. By the way, you were going to try to call the readData method from main, which can't happen without readData being static, too. I just called it from the constructor as you'll see:

Hope this helps,
Kevin


import java.io.*;

class Tutorial1
{
public Tutorial1()
{
this.readData("testfile.txt");
}

/**
* readData
* input String filename
* store the values of the third column of numbers of the data file into the member array: data
*/
public void readData(String filename)
{
try
{
File file = new File(filename);
BufferedReader reader = new BufferedReader(new FileReader(file));

String line = null;

while((line = reader.readLine()) != null)
{
System.out.println(line);
}
}
catch(FileNotFoundException ex)
{
System.out.println(ex.toString());
}
catch (IOException ex)
{
System.out.println(ex.toString());
}
}

public static void main(String args[])
{
Tutorial1 tut1 = new Tutorial1();
}
}

[conafam]

Thank you Kevin/Smeagol - that's great!

Much appreciated.

[cfc]

Are you learning Java from online tutorials? If so, I sincerely recommend getting a book, esp. to begin with and get a solid background of the language. I've been promoting Bruce Eckel's Thinking in Java books since I originally picked Java up from the 2nd edition (when J2SDK1.3 was out), and I think they're the best free resources available for learning Java. They're available for free in downloadable form, but you can also buy them on paper or CD-ROM.

http://www.mindview.net/Books/TIJ/ -- the 2nd edition was about a two week read (while doing other things of course), and I expect the third edition to take about as long to read.

Also of interest if you're using Java 1.4+ will be the java.nio packages; they're more complex to use because they're lower-level, but that also makes the new I/O system more efficient. This example, which I borrowed from Thinking in Java, 3rd Edition by Bruce Eckel (see above) will copy one file to another using the new I/O system (bytebuffers and channels):

//: c12:ChannelCopy.java
// Copying a file using channels and buffers
// {Args: ChannelCopy.java test.txt}
// {Clean: test.txt} 
import java.io.*;
import java.nio.*;
import java.nio.channels.*;

public class ChannelCopy {
  private static final int BSIZE = 1024;
  public static void main(String[] args) throws Exception {
    if(args.length != 2) {
      System.out.println("arguments: sourcefile destfile");
      System.exit(1);
    }
    FileChannel 
      in = new FileInputStream(args[0]).getChannel(),
      out = new FileOutputStream(args[1]).getChannel();
    ByteBuffer buffer = ByteBuffer.allocate(BSIZE);
    while(in.read(buffer) != -1) {
      buffer.flip(); // Prepare for writing
      out.write(buffer);
      buffer.clear();  // Prepare for reading
    }
  }
} ///:~