1. Writing Text Files

This chapter explains how to create a text file on the hard disk and how to write character data to it.

Chapter 21 used redirection to write text files. Redirection is when output that would normally go to the monitor is sent to a disk file. The program has no control of this.

In this chapter your program creates a file and writes output to it.

Chapter Topics:

Question 1:
(Review: ) What is the ancestor class of all streams that do character-oriented output?

Source: Bradley Kjell, https://chortle.ccsu.edu/Java5/Notes/chap83/ch83_1.html
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 License.

2. Writer

Answer:
Writer

Writer

Question 2:
Does the class FileWriter seem like a likely candidate for writing characters to a file?

3. FileWriter

Answer:
Yes

FileWriter

Question 3:
Say that OutputStreamWriter has a method you would like to use. Will a FileWriter object have this method?

4. Example Program

Answer:
Yes, since FileWriter inherits from OutputStreamWriter.

Example Program

import java.io.*;

class WriteTextFile
{

  public static void main ( String[] args ) throws IOException
  {
    String fileName = "reaper.txt" ;

    FileWriter writer = new FileWriter( fileName );

    writer.write( "Behold her, single in the field,\n"  );  
    writer.write( "Yon solitary Highland Lass!\n"  );  
    writer.write( "Reaping and singing by herself;\n" );  
    writer.write( "Stop here, or gently pass!\n"  );  

    writer.close();
  }
}

Question 4:
Is an IOException a checked exception?

5. Example Run

Answer:
Yes, an IOException is a checked exception, and so must be caught or thrown to the caller. (More on this later.)

Example Run

C:\Programs>DIR

06/04/00  07:55p        <DIR>          .
06/04/00  07:55p        <DIR>          ..
06/04/00  07:55p                   693 WriteTextFile.class
06/04/00  07:55p                   475 WriteTextFile.java

C:\Programs>java  WriteTextFile

C:\Programs>DIR

06/04/00  07:56p        <DIR>          .
06/04/00  07:56p        <DIR>          ..
06/04/00  07:56p                   120 reaper.txt
06/04/00  07:55p                   693 WriteTextFile.class
06/04/00  07:55p                   475 WriteTextFile.java

C:\Programs>TYPE REAPER.TXT
Behold her, single in the field,
Yon solitary Highland Lass!
Reaping and singing by herself;
Stop here, or gently pass! 

Question 5:
Could you edit reaper.txt with a text editor?

6. Character Set Transformation

Answer:
Sure. It is a text file.

Character Set Transformation

Question 6:
What do you suppose closing a file does?

7. Closing a File

Answer:
Closing a file asks the system to finish all activity with the file and to ensure that it is safely on the disk.

Closing a File

Question 7:
Can a file be written while it is closed?

8. FileWriter Constructors

Answer:
No

FileWriter Constructors

FileWriter(String fileName)
FileWriter(String fileName, boolean append) 

public static void main ( String[] args ) throws IOException
{
  String fileName = "reaper.txt" ;

  FileWriter writer = new FileWriter( fileName );
  
    . . .

Question 8:
What happens if the file name is not correct? 

9. IOExceptions

Answer:
An IOException is thrown.

IOExceptions

                            
import java.io.*;

class WriteTextFile2
{

  public static void main ( String[] args ) 
  {
    String fileName = "reaper.txt" ;

    try
    {  
      // append characters to the file
      FileWriter writer = new FileWriter( fileName, true );

      writer.write( "Alone she cuts and binds the grain,\n"  );  
      writer.write( "And sings a melancholy strain;\n"  );  
      writer.write( "O listen! for the Vale profound\n" );  
      writer.write( "Is overflowing with the sound.\n\n"  );  

      writer.close();
    }
    catch ( IOException iox )
    {
      System.out.println("Problem writing " + fileName );
    }
  }
}

Question 9:
If you are running a Microsoft operating system, change the permissions of the file reaper.txt to read only. 
(Right-click on the file name in Explorer and then go to properties). Now run the program again. What happens?

10. The write() Method

Answer:
An IOException is thrown by FileWriter and caught in the catch block.

The write() Method

public void write(String str)  throws IOException

int answer;
. . .
stream.write( "The answer is: " + answer) 

Question 10:
Does the disk file contain int data?

11. Summary of Class FileWriter

Answer:
No, the disk file is a text file and contains only characters.

Summary of Class FileWriter

FileWriter(String fileName) 
   An IOException is thrown if the file cannot be created.
            
FileWriter(String fileName, boolean append)            
   An IOException is thrown if the file cannot be opened for appending.

public void close() throws IOException
    Flush the stream and close the file.

public void flush() throws IOException
    Flush the stream.

public void write(String str) throws IOException
    Write a string.

Question 11:
Why not do a flush() after each write() to be sure that all the data is written to the disk?

12. File Name from User Input

Answer:
This will slow down disk I/O.

File Name from User Input

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

class CreateFile
{
  public static void main ( String[] args ) 
  {

    // Get filename and create the file
    FileWriter writer = null;
    Scanner scan = new Scanner( System.in );
    String fileName = "";
    System.out.print("Enter Filename-->");                    // Ask for the file name
    
    try
    {
      fileName = scan.next();                                  // Get the file name
      writer = new FileWriter( fileName );                     // Create the file
    }
    catch  ( IOException iox )
    {
      System.out.println("Error in creating file");            // On failure, write error message
      return;                                                  // Return 
    } 
      
    // Write the file.
    try
    {  
      writer.write( "Behold her, single in the field,\n"  );   // Write text to the file
      writer.write( "Yon solitary Highland Lass!\n"  );  
      writer.write( "Reaping and singing by herself;\n" );  
      writer.write( "Stop here, or gently pass!\n"  );  
      writer.close();                                          // Close the file
    }
    catch ( IOException iox )
    {
      System.out.println("Problem writing " + fileName );     // On failure, write error message
    }
  }
}

Question 12:
What happens (in this program) if the close() method fails?

13. The BufferedWriter Stream

Answer:
The close() method will throw an exception, which will be caught. The catch block will write an error message that is not 
 really correct. You could fix the error message, or add another try/catch structure to the program that deals only with closing the file.

The BufferedWriter Stream

Disk input and output is more efficient when a buffer is used. For our small example programs it doesn't matter much. However, programs that do extensive I/O should use buffers. Use BufferedWriter to do this with a character output stream.

BufferedWriter(Writer out)  
    Construct a buffered character-output stream 

Since a FileWriter is a Writer it is the correct type for the parameter. Here is how this might be done:

BufferedWriter out
   =  new BufferedWriter(new FileWriter("stuff.txt"));  

Question 13:
Do all operating systems end lines of text in the same way?

14. PrintWriter

Answer:
No.

PrintWriter

Question 14:
Can a PrintWriter be used alone?

15. Updated Example

Answer:
No. It cannot be the final destination of data, so it should be connected to some other stream.

Updated Example

import java.io.*;
class WriteTextFile3
{
  public static void main ( String[] args ) 
  {
    String fileName = "reaper.txt" ;
    PrintWriter print = null;

    try
    {       
      print = new PrintWriter( new BufferedWriter( new FileWriter( fileName  ) ) );
    }
    catch ( IOException iox )
    {
      System.out.println("Problem writing " + fileName );
    }

    print.println( "No Nightingale did ever chaunt"  );  
    print.println( "More welcome notes to weary bands"  );  
    print.println( "Of travellers in some shady haunt," );  
    print.println( "Among Arabian sands."  );  

    print.close();
  }
}

Question 15:
Is close() necessary in this program?

16. Summary of Class PrintWriter

Answer:
Yes, especially when buffers are used you should flush pending output before the program ends.
Detail: The close() method of PrintWriter does not throw an IOException, so it can be outside of any try block.

Summary of Class PrintWriter

Constructors

PrintWriter(Writer out) 
   Create a new PrintWriter and connect it to the Writer out.
   Automatic line flushing is not enabled.

PrintWriter(Writer out, boolean autoFlush) 
   Create a new PrintWriter and connect it to the Writer out.
   Automatic line flushing is enabled if autoFlush is true.

Methods

public boolean checkError()
    Flush the stream. If there has been an error in output the
    method returns true.

public void close() 
    Flush the stream and close the file.

public void flush()  
    Flush the stream.

public void print(char c)
    Print the character neld in c.

public void print(double d)
    Translate into characters and print the double value d.

public void print(float f)
    Translate into characters and print the float value f.

public void print(int i)
    Translate into characters and print the int value i.

public void print(String s)
    Print the String s.

public void print( various other data types )
    See your complete documentation.
   
public void println() 
    Terminate the current output line and (possibly) flush the stream.

public void println( various  data types )
    See Java on-line documentation.

Question 16:
Can you pretty much print any type of data you want?

17. Example Program

Answer:
Yes. No need to memorize that list of methods.

Example Program

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

class PowerTable
{
  public static void main ( String[] args ) 
  {
    // Get filename and create the file
    PrintWriter printer = null;
    Scanner scan = new Scanner( System.in );
    String fileName = "";

    System.out.print("Enter Filename-->");  
    try
    {
      fileName = scan.next();
      
      // create the PrintWriter and enable automatic flushing
      printer = new PrintWriter( new BufferedWriter( new FileWriter( fileName )), true );
    }
    catch ( IOException iox )
    {
      System.out.println("Error in creating file");
      return;
    }
      
    // Write out the table.
    int value = 1;
    printer.println( "Power\tValue"  );
    for ( int pow=0; pow<=20; pow++ )
    {
      printer.print  ( pow   );  
      printer.print  ( '\t'  );  
      printer.println(  value  );  
      value = value*2;
    }
    printer.close();
   
  }
 
}

Question 17:
Instead of using three statements in a row, would the following have worked as well?
out.println( pow + "\t" + value  ); 

18. End of Chapter

Answer:
Yes. The argument pow + "\t" + value is automatically converted to a String. The method println( String ) is then called.

End of Chapter

You have reached the end this chapter. You may wish to review the following.

• Class FileWriter.
• UTF and character translation.
• Closing a file.
• FileWriter Constructors.
• Catching IOExceptions
• The write() method.
• Methods of FileWriter.
• Class BufferedWriter
• Class PrintWriter
• Methods of PrintWriter