How to read from a text file one character at a time?

Hello
I wish to read from a text file in a for loop and that on every iteration i read one charachter and proceed to the next one.
can anyone help me?
Lavi

lava wrote:
I wish to read from a text file in a for loop and that on every iteration i read one charachter and proceed to the next one.
can anyone help me?
Some additional comments:
You really don't want to read any file one character at a time, because it is highly inefficient. More typically, you read the entire file into memory with one operation (or at least a large chunk, if the file is gigantic) and then do the rest of the operations in memory. One easy way to analyze it one byte at a time would be to use "string to byte array" and then autoindex into a FOR loop, for example.
Of course you could also read the file directly as a U8 array instead of a string.
Message Edited by altenbach on 06-10-2008 08:57 AM
LabVIEW Champion . Do more with less code and in less time .

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Read data from a text file, one line at a time.

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I need to read from a text file. When the token encounters a particular word (command) I need to read the next line and perform some actions. However, this part is working but it is repeating the values again and again until it encounters the next particular word (command). Hope that someone will help me out, as always when I posted a problem in these forums.
SetOperations class - contains the set methods
// Imported packages.========================================================
import java.util.Vector;
import java.util.Iterator;
// Public class SetOperations.===============================================
public class SetOperations
     // Instance variables.===================================================
     private Vector v = null; // Creates new instance of vector.
     protected int memberCount;
     // Constructor.==========================================================
     public SetOperations()
          v = new Vector();
     } // end constructor.
     // Method isMember.======================================================
     * Checks whether the element is already a member of the set.
     * @return True if Vector v contains Object member.
     public boolean isMember(Object member)
          if (member != null) // only if Object member is not null.
               return v.contains(member); // returns true if vector already contains member.
          else
               return false; // returns false if vector does not contain member.
     } // end public boolean isMember(Object member).
     // Method addMember.=====================================================
     * Adds a member to the set.
     * @return Adds Object member to Vector v.
     public void addMember(Object member)
          //if (! v.contains(member)) // only if element is not already a member.
          if (isMember(member) == false) // only if element is not already a member.
               v.add(member); // adds a member.
     } // end public void addMember(Object member).
     // Method countMember.===================================================
     * Returns the number of members present in the vector.
     * @return Number of elements present in the vector.
     public int countMember()
          return v.size();
     } // end public int countMember().
     // Method isSetEmpty.====================================================
     * Returns true if set is empty.
     * @return True if no elements are present in Vector v.
     public boolean isSetEmpty()
          return v.size() == 0; // returns 0 if no elements are present in the vector.
     } // end of public boolean isSetEmpty().
     // Method printMember.===================================================
     * Displays member/s of the set.
     * @return Prints element/s present in the vector.
     public void printMember()
          for (int i = 0; i < v.size(); i++) // iterates through present members.
               System.out.println("[" + i + "] " + v.get(i)); // displays member/s present in the vector.
     } // end of public void printMember().
} // end public class SetOperations.
SetTextLauncher class - reads from a text file and implements the set operations
// Imported packages.========================================================
import java.util.*;
import java.io.*;
// Public class SetTestLauncher.=============================================
public class SetTestLauncher
     // Main method public static void main(String args[]).===================
     public static void main(String args[])
          displayFile("test.txt"); // outputs result from text file.
     // method to display a file on screen
     public static void displayFile (String textFile)
          // Instance variables.===============================================
          // Creates new instances of SetOperations.
          SetOperations setA = new SetOperations();
          SetOperations setB = new SetOperations();
          SetOperations setC = new SetOperations();
          SetOperations setD = new SetOperations();
          SetOperations setE = new SetOperations();
          // Initialisation.
          String line = "", nextLine = "";
          FileReader fr = null;
          try
               // Opens the file with the FileReader data sink stream.
               fr = new FileReader(textFile);
               // Converts the FileReader input stream with the BufferedReader processing stream.
               BufferedReader br = new BufferedReader(fr);
               // Iterates through text file reading lines until end of text lines.
               while (line != null)
                    line = br.readLine(); // reads one line at a time.
                    if(line == null) break; // when the line is null break the loop.
                    // Creates a new instace of StringTokenizer.
                    StringTokenizer st = new StringTokenizer(line);
                    // Loops until there are no more tokens.
                    while (st.hasMoreTokens())
                         String token = st.nextToken(); // reads next token.
                         // Only if the token encounters the String "membera".
                         if(token.equals("membera"))
                              nextLine = br.readLine(); // gets next line.
                              setA.addMember(nextLine); // adds a member to the set.
                              // Displays members present in the set if vector is not empty.
                              if (! setA.isSetEmpty())
                                   setA.printMember(); // print members present.
                              // Displays the number of member/s present in the vector.
                              System.out.println("Number of set members: " + setA.countMember());
          // Catches and displays exceptions.
          catch (FileNotFoundException exp)
               System.out.println(exp.getMessage());
               exp.printStackTrace();
          catch (IOException exp)
               System.out.println(exp.getMessage());
               exp.printStackTrace();
          finally
               try
                    // if file is found
                    if (fr != null)
                         // close file
                         fr.close();
               catch (IOException exp)
                    exp.printStackTrace();
     } // end public static void main(String args[]).
} // end public class SetTestLauncher.

Thanks for your interest. Please ignore SetOperations class, it is just the class containing the methods and it works correctly since I checked it without reading from a text file. I marked the part where I think lies my problem in class SetTestOperations.
The information in the text file is as follows:
membera
Hillman
membera
Skoda
membera
Honda
membera
Toyota
and the result is:
[0] Hillman
Number of set members: 1
[0] Hillman
[1] Skoda
Number of set members: 2
[0] Hillman
[1] Skoda
[2] Honda
Number of set members: 3
[0] Hillman
[1] Skoda
[2] Honda
[3] Toyota
Number of set members: 4
instead of just one set:
[0] Hillman
[1] Skoda
[2] Honda
[3] Toyota
Number of set members: 4
Hope it is easier to understand like this.
Regards
Marco
I need to read from a text file. When the token
encounters a particular word (command) I need to read
the next line and perform some actions. However, this
part is working but it is repeating the values again
and again until it encounters the next particular
word (command). Hope that someone will help me out,
as always when I posted a problem in these forums.
SetOperations class - contains the set
methods
// Imported
packages.=============================================
===========
import java.util.Vector;
import java.util.Iterator;
// Public class
SetOperations.========================================
=======
public class SetOperations
// Instance
e
variables.============================================
=======
private Vector v = null; // Creates new instance of
f vector.
     protected int memberCount;
Constructor.==========================================
================
     public SetOperations()
          v = new Vector();
     } // end constructor.
// Method
d
isMember.=============================================
=========
* Checks whether the element is already a member of
f the set.
     * @return True if Vector v contains Object member.
     public boolean isMember(Object member)
if (member != null) // only if Object member is not
ot null.
return v.contains(member); // returns true if
if vector already contains member.
          else
return false; // returns false if vector does not
not contain member.
     } // end public boolean isMember(Object member).
// Method
d
addMember.============================================
=========
     * Adds a member to the set.
     * @return Adds Object member to Vector v.
     public void addMember(Object member)
//if (! v.contains(member)) // only if element is
is not already a member.
if (isMember(member) == false) // only if element
nt is not already a member.
               v.add(member); // adds a member.
     } // end public void addMember(Object member).
// Method
d
countMember.==========================================
=========
* Returns the number of members present in the
e vector.
     * @return Number of elements present in the vector.
     public int countMember()
          return v.size();
     } // end public int countMember().
// Method
d
isSetEmpty.===========================================
=========
     * Returns true if set is empty.
* @return True if no elements are present in Vector
r v.
     public boolean isSetEmpty()
return v.size() == 0; // returns 0 if no elements
ts are present in the vector.
     } // end of public boolean isSetEmpty().
// Method
d
printMember.==========================================
=========
     * Displays member/s of the set.
     * @return Prints element/s present in the vector.
     public void printMember()
for (int i = 0; i < v.size(); i++) // iterates
es through present members.
System.out.println("[" + i + "] " + v.get(i)); //
// displays member/s present in the vector.
     } // end of public void printMember().
} // end public class SetOperations.
SetTextLauncher class - reads from a text file
and implements the set operations
// Imported
packages.=============================================
===========
import java.util.*;
import java.io.*;
// Public class
SetTestLauncher.======================================
=======
public class SetTestLauncher
// Main method public static void main(String
g args[]).===================
     public static void main(String args[])
displayFile("test.txt"); // outputs result from
om text file.
     // method to display a file on screen
     public static void displayFile (String textFile)
// Instance
ce
variables.============================================
===
          // Creates new instances of SetOperations.
          SetOperations setA = new SetOperations();
          // Initialisation.
          String line = "", nextLine = "";
          FileReader fr = null;
          try
// Opens the file with the FileReader data sink
ink stream.
               fr = new FileReader(textFile);
// Converts the FileReader input stream with the
the BufferedReader processing stream.
               BufferedReader br = new BufferedReader(fr);
// Iterates through text file reading lines until
til end of text lines.
               while (line != null)
line = br.readLine(); // reads one line at a
at a time.
if(line == null) break; // when the line is null
null break the loop.
                    // Creates a new instace of StringTokenizer.
                    StringTokenizer st = new StringTokenizer(line);
                    // Loops until there are no more tokens.
                    while (st.hasMoreTokens())
String token = st.nextToken(); // reads next
next token.
// Only if the token encounters the String
tring "membera".
                         if(token.equals("membera"))
                              // *****THE PROBLEM LIES HERE....I GUESS
// need to read the next line after encountering the word membera in text file
nextLine = br.readLine(); // gets next line.
setA.addMember(nextLine); // adds a member to
ber to the set.
// Displays members present in the set if
set if vector is not empty.
                              if (! setA.isSetEmpty())
                                   setA.printMember(); // print members present.
// Displays the number of member/s present in
ent in the vector.
System.out.println("Number of set members: " +
s: " + setA.countMember());
          // Catches and displays exceptions.
          catch (FileNotFoundException exp)
               System.out.println(exp.getMessage());
               exp.printStackTrace();
          catch (IOException exp)
               System.out.println(exp.getMessage());
               exp.printStackTrace();
          finally
               try
                    // if file is found
                    if (fr != null)
                         // close file
                         fr.close();
               catch (IOException exp)
                    exp.printStackTrace();
     } // end public static void main(String args[]).
} // end public class SetTestLauncher.

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Message Edité par chilly charly le 01-13-2009 09:29 PM
Chilly Charly (aka CC)
E-List Master - Kudos glutton - Press the yellow button on the left...
Attachments:
Example_VI.png ‏10 KB

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