Trying to read a file, then writing the info into another file

[bigsonny]

Hello JF residents,

I have a new problem, still going through the Java tutorial over at the Oracle site. I am excited because I went through the generic tutorial and while I get it conceptually, I am not yet comfortable using it. Same can be said of the Exceptions tutorial. Asides from throws IOException which I mostly use because I saw it everywhere, it is not yet instinctive, but I'm working on that.

So what I am excited about? Well, I have arrived to the Essential classes, specifically going through "Basic I/O" which is the class that I had been looking to learn the most from.

So here is the problemo. I just went through the Scanning lesson plan which has a very nice little class called ScanXan which read from a file and prints it back to the screen. So I tried it, understood everything and thought...yay. So then I thought this is good and all, but let's print this output to a file and not just the screen, so Modified to the code to the following:

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


public class ScanXan2 {
    public static void main(String[] args) throws IOException {
        Scanner s = null;
		  PrintWriter output = null;
		  
		  
        try {
            s = new Scanner(new BufferedReader(new FileReader("xanadu.txt")));
				output = new PrintWriter (new FileWriter ("xanaduout.txt"));
				
            while (s.hasNext()) {
                System.out.println(s.next());
					 output.println(s.next());
					 
            }
        } finally {
            if (s != null) {
                s.close();
            }
        }
    }
}

The outputs are:
1) It prints each token to the screen, one token per line.
2) It creates my file "xanaduout.txt"
3) It DOES NOT print the token to the screen.

So then I went back and re-read the Scanner class. It says that it is "A simple text scanner which can parse primitive types and strings using regular expressions" so I thought, well, maybe I need a string, so I assigned the readout to a String type which I then try to print to the file:

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


public class ScanXan2 {
    public static void main(String[] args) throws IOException {
        Scanner s = null;
		  PrintWriter output = null;
		  
		  
        try {
            s = new Scanner(new BufferedReader(new FileReader("xanadu.txt")));
				output = new PrintWriter (new FileWriter ("xanaduout.txt"));
				
            while (s.hasNext()) {
                System.out.println(s.next());
					 String l = s.next();
					 output.println(l);
					 
            }
        } finally {
            if (s != null) {
                s.close();
            }
        }
    }
}

Outcome? same as before, no text in my file. I am wondering if you would be able to point me in the right direction. What am I not understanding about these classes?

thanks!

[Dark]

Why don't you just use the FileReader/FileWriter instead of ScanXan?

[bigsonny]

because I'm new and I'm still trying to get a hold of this.

[bigsonny]

Why don't you just use the FileReader/FileWriter instead of ScanXan?

Actually I re-read this and I am confused. I am using both classes. They're constructed within my class. Can you take a look at the code and give me some indication of why I am not seeing an output in the file? The file is created, but it's empty.

[Norm]

Observations:
You have 2 next() calls for 1 hasNext() call
You don't printStackTrace() to show errors
you don't close the output file.

[bigsonny]

Observations:
You have 2 next() calls for 1 hasNext() call
You don't printStackTrace() to show errors
you don't close the output file.

Hello Norm,

I did two of the 3.

import java.io.*;
import java.util.Scanner;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.IOException;


public class ScanXan2 {
    public static void main(String[] args) throws IOException {
	 		//declaration of a Scanner object named "s" and assigning a null value to it.
        Scanner s = null;
		  //declaration of a PrintWriter object named "output" and assigning a null value to it.
		  PrintWriter output = null;
		  
		  
        try {
		  		//the Scanner object s is now constructed with 
            s = new Scanner(new BufferedReader(new FileReader("xanadu.txt")));
				output = new PrintWriter (new FileWriter ("xanaduout.txt"));
				
				//This first conditional/loop will print to the screen each token, separated by a space
            while (s.hasNext()) {
                System.out.println(s.next());				 
					 }
				//This second conditional/loop will hopefully print to the file.
				while (s.hasNext()) {
					output.println(s.next());
					 }
				}					 
            
         finally {
		  		//closing s Scanner
            if (s != null) {
                s.close();
            }
				//closing output PrintWriter
				if (output != null) {
					output.close();
				}
        }
    }
}

I don't know how to use printStackTrace(). I tried printing it to the screen, but I received the following error:

ScanXan2.java:26: cannot find symbol
symbol  : method printStackTrace(java.lang.String)
location: class java.io.PrintStream
					 System.out.printStackTrace(s.next());				 
					           ^
1 error

so I removed it from the code. I went to the API but the first method asks for a

 catch (HighLevelException e) {e.printStackTrace(); }

I tried that and instead ended up with the following error:

ScanXan2.java:33: cannot find symbol
symbol  : class HighLevelException
location: class ScanXan2
			catch (HighLevelException e) {
			       ^
1 error

so then I tried to system.err.printStackTrace(); and I received two errors, the one above and another cannot find symbol for the .err

 ----jGRASP exec: javac -g ScanXan2.java

ScanXan2.java:25: cannot find symbol
symbol  : method printStackTrace()
location: class java.io.PrintStream
					 System.err.printStackTrace();
					           ^
ScanXan2.java:33: cannot find symbol
symbol  : class HighLevelException
location: class ScanXan2
			catch (HighLevelException e) {
			       ^
2 errors

 ----jGRASP wedge2: exit code for process is 1.
 ----jGRASP: operation complete.

[Norm]

Usually like this at end of try{ block:

}catch(Exception e) {e.printStackTrace();}

[bigsonny]

Thanks. I added it, resulting in the following:

import java.io.*;
import java.util.Scanner;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.IOException;


public class ScanXan2 {
    public static void main(String[] args) throws IOException {
	 		//declaration of a Scanner object named "s" and assigning a null value to it.
        Scanner s = null;
		  //declaration of a PrintWriter object named "output" and assigning a null value to it.
		  PrintWriter output = null;
		  
		  
        try {
		  		//the Scanner object s is now constructed with 
            s = new Scanner(new BufferedReader(new FileReader("xanadu.txt")));
				output = new PrintWriter (new FileWriter ("xanaduout.txt"));
				
				//This first conditional/loop will print to the screen each token, separated by a space
            while (s.hasNext()) {
                System.out.println(s.next());
					 				 
					 }
				//This second conditional/loop will hopefully print to the file.
				while (s.hasNext()) {
					output.println(s.next());
					 }
				}
				catch (Exception e) {
					e.printStackTrace();
					}					 
            
         finally {
		  		//closing s Scanner
            if (s != null) {
                s.close();
            }
				//closing output PrintWriter
				if (output != null) {
					output.close();
				}
        }
    }
}

but my output file is still empty. Any other suggestions?

[Norm]

Are all the lines in the file printed?

Add a println to show the value of hasNext() at this point in your code:

              
                               System.out.println("hasNext=" + s.hasNext()); // show if more lines
                               //This second conditional/loop will hopefully print to the file.
				while (s.hasNext()) {
					output.println(s.next());
                                 }

[bigsonny]

Are all the lines in the file printed?

Add a println to show the value of hasNext() at this point in your code:

              
                               System.out.println("hasNext=" + s.hasNext()); // show if more lines
                               //This second conditional/loop will hopefully print to the file.
				while (s.hasNext()) {
					output.println(s.next());
                                 }

Thanks. I added it and it prints false once it runs out, but It is still not printing to the file. I'll think about it and see what I get. thanks!

[Norm]

Are all the lines in the file printed?

[bigsonny]

Are all the lines in the file printed?

No Norm. The file is created, but there are no lines. No text.

[bigsonny]

Hello Norm,

good news...well sort of. I overcame my semantic error, so the code does what I wanted it to do. I don't think it's the best or the cleanest way to do it, but it's a start in the right direction in terms of problem solving. Please see below:

import java.util.Scanner;
import java.io.FileReader;
import java.io.FileWriter;
import java.io.BufferedReader;
import java.io.PrintWriter;
import java.io.IOException;


public class ScanXan2 {
    public static void main(String[] args) throws IOException {
	 		//declaration of a Scanner object named "s" and assigning a null value to it.
        Scanner s = null;
		  Scanner t = null;
		  //declaration of a PrintWriter object named "output" and assigning a null value to it.
		  PrintWriter output = null;
		  
		  
        try {
		  		//the Scanner object s is now constructed with 
            s = new Scanner(new BufferedReader(new FileReader("xanadu.txt")));
				t = new Scanner(new BufferedReader(new FileReader("Xanadu.txt")));
				output = new PrintWriter (new FileWriter ("xanaduout.txt"));
				
				//This first conditional/loop will print to the screen each token, separated by a space
                                while (s.hasNext()&& (t.hasNext())) {
                                System.out.println(s.next());
				output.println(t.next());
					 				 
					 }
				//This second conditional/loop will hopefully print to the file.
				System.out.println("hasNext=" + s.hasNext()); // show if more lines
                               //This second conditional/loop will hopefully print to the file.
				while (s.hasNext()) {
					output.println(s.next());
                                 }
				}
				catch (Exception e) {
					e.printStackTrace();
					}					 
            
         finally {
		  		//closing s Scanner
            if (s != null) {
                s.close();
            }
				//closing output PrintWriter
				if (output != null) {
					output.close();
				}
        }
    }
}

So it's all thanks to you actually. The code you gave me where you asked me to check if there is something left to read returned false. So I realize that by time I got to scanning the file and printing it into the new file, there was nothing left outside of the while loop. So I placed it inside the first while look and it still did not work. However I created a second scanner object, I could then printwrite it into the file with each token occupying only one line. Thank you for your help.

So while I am glad that I got it to do what I wanted, I know the code is somewhat sloppy and perhaps not the best way to about it. Any criticism by anyone is highly welcome. Thanks!

[Norm]

while (s.hasNext()&& (t.hasNext())) {
                                System.out.println(s.next());
				output.println(t.next());

Instead of using two streams in parallel, read the line into a string and then show it on the screen and write it to the file:

                         while (s.hasNext()) {
                                String nexLine = s.next();   // read the next line
                                System.out.println(nexLine);    // show on screen
				output.println(nexLine);     // write to file

[bigsonny]

Got it. Thanks.