Programming Forums > Application Development > Java

Eric the Red · Apr 5th, 2006, 12:02 AM

I'm not to sure how to move the pointer on the file your working with. For example in the following code: the 2 print statements (in blue) read lines 1 - 3. but the writting in orange continues reading the file. How do i move the pointer up to line 1 again to that the writting in orange does not continue from where the writting in blue left off ?

(Toggle Plain Text)

  BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt"));

                //int intNumberofLines = 0; // default 0 because there is always 1 line to read

                // first we get all the data so that it isn't written over
                
                intNumberofLines = Integer.valueOf (input2.readLine ()).intValue (); 
                c.print(input2.readLine()); 
                c.print(input2.readLine());  
                //c.print ("2nd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); 
                //c.print ("3rd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); 
                //c.print ("number of lines is" + intNumberofLines);

               // String inputString [] = new String [intNumberofLines]; // array large enough to hold all text data
                for (int y = 0 ; y < (intNumberofLines - 1) ; y++) // +1 because we've already read the int for line 1.
                {
                    inputString [y] = input2.readLine (); // because array starts at 0 not 1.
                    c.print ("String is: " + inputString [y]);
                }

                inputStringFinal = new String [intNumberofLines + 1];  // +1 because the tempLicense is added to the array.
                blnStringDeclared = true; // so it can be used when (inputAns = 1)
                
                    // cloning array and adding the final License
                    for (int i = 0 ; i < intNumberofLines ; i++) // cloning the array
                {
                    inputStringFinal [i] = tempLicense;
                }

                inputStringFinal [intNumberofLines] =  tempLicense; // the last boundary is used for the license just created
                
                c.print ("first line 1: " + input2.readLine());
                c.print ("second line 2: " + input2.readLine());
                c.print ("third line 3: " + input2.readLine());

titaniumdecoy · Apr 5th, 2006, 12:55 AM

If you really want to rewind the BufferedReader, you'll find the mark() and reset() methods useful.

However, I suggest that instead you store all the data you read in from the BufferedReader initially, close() it, and use the data you have already stored rather than rereading it.

For example, why not replace

(Toggle Plain Text)

c.print ("first line 1: " + input2.readLine());

with

(Toggle Plain Text)

c.print ("first line 1: " + inputStringFinal[0]);

Eric the Red · Apr 5th, 2006, 2:14 AM

Quote:

Originally Posted by titaniumdecoy

If you really want to rewind the BufferedReader, you'll find the mark() and reset() methods useful.

However, I suggest that instead you store all the data you read in from the BufferedReader initially, close() it, and use the data you have already stored rather than rereading it.

For example, why not replace

(Toggle Plain Text)

c.print ("first line 1: " + input2.readLine());

with

(Toggle Plain Text)

c.print ("first line 1: " + inputStringFinal[0]);

Thanks you!! you were right. better to read in the entire file first.

Eric the Red · Apr 12th, 2006, 11:46 PM

I have this line of code

(Toggle Plain Text)

BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt"));

I'm wondering if anyone knows how to catch the exception where
"if there's no output.txt found" create it.

Arevos · Apr 13th, 2006, 3:29 AM

Catch "FileNotFoundException".

Eric the Red · Apr 13th, 2006, 4:57 AM

Quote:

Originally Posted by Arevos

Catch "FileNotFoundException".

k thx. Goodnight

Eric the Red · Apr 13th, 2006, 7:33 AM

Well i still can't get this to work. The error has something to do with the 'try' and 'catch' statement. Anyone care to provide some input?

error code:

(Toggle Plain Text)

The constructor "FileReader" can throw the checked exception "java.io.FileNotFoundException",
but it's invocation is neither enclosed in a try statement that can catch that exception nor in the body 
of the method or constructor that "throws" that exception.

program code. Note the blue writting is where the error comes from.

(Toggle Plain Text)

class Database 
        {       
            public int lengthofFile; // holds the file length
            public String tempString = ""; // holds the added value from main. This value is to be added to the list
            public String oldFile [] = new String [1]; // this will hold the old file
            public String newFile [] = new String [1]; // this will hold the updated file
            public BufferedReader input2;
            // the contructor. When an object is created this is the default method used.
            public Database ()
            {

                // before we can modify the file we need to know how many lines it is, at the moment.
                input2 = new BufferedReader (new FileReader  ("C:\\output.txt"));
                lengthofFile = Integer.valueOf (input2.readLine ()).intValue ();
                try
                {
                 c.print ("I'm in Try");
                }
                catch (IOException input2)
                {
                    c.println ("Input error");
                   /* sets the length of the file
                    sothatwecanmodify it later on*/
                    oldFile = new String [lengthofFile];
                    newFile = new String [lengthofFile + 1];
                }
            }
}

SugarHigh · Apr 28th, 2006, 11:03 PM

ignore this

SugarHigh · Apr 28th, 2006, 11:05 PM

The problem is that you either have to do a try-catch block that catches an IOException. You must do this for anything that has to do with file IO.

Here is what is should look like:

(Toggle Plain Text)

try{
    input2 = new BufferedReader (new FileReader  ("C:\\output.txt"));
} catch(IOException e){
    // other code
}

NOTE: If you are trying to do file IO in a method as opposed to a constructor, you can just append "throws IOException" to the method name

(Toggle Plain Text)

Example:

public String exampleMethod(BufferedReader b) throws IOException{
     // Code
};

This way you don't have to use a try-catch block each time you deal with file IO, at least in that method.

Apr 5th, 2006, 12:02 AM	#1
Eric the Red Hobbyist Programmer Join Date: Feb 2006 Posts: 214 Rep Power: 0	BufferedReader I'm not to sure how to move the pointer on the file your working with. For example in the following code: the 2 print statements (in blue) read lines 1 - 3. but the writting in orange continues reading the file. How do i move the pointer up to line 1 again to that the writting in orange does not continue from where the writting in blue left off ? (Toggle Plain Text) BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt")); //int intNumberofLines = 0; // default 0 because there is always 1 line to read // first we get all the data so that it isn't written over intNumberofLines = Integer.valueOf (input2.readLine ()).intValue (); c.print(input2.readLine()); c.print(input2.readLine()); //c.print ("2nd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); //c.print ("3rd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); //c.print ("number of lines is" + intNumberofLines); // String inputString [] = new String [intNumberofLines]; // array large enough to hold all text data for (int y = 0 ; y < (intNumberofLines - 1) ; y++) // +1 because we've already read the int for line 1. { inputString [y] = input2.readLine (); // because array starts at 0 not 1. c.print ("String is: " + inputString [y]); } inputStringFinal = new String [intNumberofLines + 1]; // +1 because the tempLicense is added to the array. blnStringDeclared = true; // so it can be used when (inputAns = 1) // cloning array and adding the final License for (int i = 0 ; i < intNumberofLines ; i++) // cloning the array { inputStringFinal [i] = tempLicense; } inputStringFinal [intNumberofLines] = tempLicense; // the last boundary is used for the license just created c.print ("first line 1: " + input2.readLine()); c.print ("second line 2: " + input2.readLine()); c.print ("third line 3: " + input2.readLine()); BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt")); //int intNumberofLines = 0; // default 0 because there is always 1 line to read // first we get all the data so that it isn't written over intNumberofLines = Integer.valueOf (input2.readLine ()).intValue (); c.print(input2.readLine()); c.print(input2.readLine()); //c.print ("2nd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); //c.print ("3rd line is: " + Integer.valueOf (input2.readLine ()).intValue ()); //c.print ("number of lines is" + intNumberofLines); // String inputString [] = new String [intNumberofLines]; // array large enough to hold all text data for (int y = 0 ; y < (intNumberofLines - 1) ; y++) // +1 because we've already read the int for line 1. { inputString [y] = input2.readLine (); // because array starts at 0 not 1. c.print ("String is: " + inputString [y]); } inputStringFinal = new String [intNumberofLines + 1]; // +1 because the tempLicense is added to the array. blnStringDeclared = true; // so it can be used when (inputAns = 1) // cloning array and adding the final License for (int i = 0 ; i < intNumberofLines ; i++) // cloning the array { inputStringFinal [i] = tempLicense; } inputStringFinal [intNumberofLines] = tempLicense; // the last boundary is used for the license just created c.print ("first line 1: " + input2.readLine()); c.print ("second line 2: " + input2.readLine()); c.print ("third line 3: " + input2.readLine()); __________________ Death smiles at us all. All a man can do is smile back.

Apr 5th, 2006, 12:55 AM	#2
titaniumdecoy Expert Programmer Join Date: Nov 2005 Posts: 843 Rep Power: 3	If you really want to rewind the BufferedReader, you'll find the mark() and reset() methods useful. However, I suggest that instead you store all the data you read in from the BufferedReader initially, close() it, and use the data you have already stored rather than rereading it. For example, why not replace (Toggle Plain Text) c.print ("first line 1: " + input2.readLine()); c.print ("first line 1: " + input2.readLine()); with (Toggle Plain Text) c.print ("first line 1: " + inputStringFinal[0]); c.print ("first line 1: " + inputStringFinal[0]);

Apr 12th, 2006, 11:46 PM	#4
Eric the Red Hobbyist Programmer Join Date: Feb 2006 Posts: 214 Rep Power: 0	I have this line of code (Toggle Plain Text) BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt")); BufferedReader input2 = new BufferedReader (new FileReader ("C:\\output.txt")); I'm wondering if anyone knows how to catch the exception where "if there's no output.txt found" create it. __________________ Death smiles at us all. All a man can do is smile back.

Apr 13th, 2006, 7:33 AM	#7
Eric the Red Hobbyist Programmer Join Date: Feb 2006 Posts: 214 Rep Power: 0	Well i still can't get this to work. The error has something to do with the 'try' and 'catch' statement. Anyone care to provide some input? error code: (Toggle Plain Text) The constructor "FileReader" can throw the checked exception "java.io.FileNotFoundException", but it's invocation is neither enclosed in a try statement that can catch that exception nor in the body of the method or constructor that "throws" that exception. The constructor "FileReader" can throw the checked exception "java.io.FileNotFoundException", but it's invocation is neither enclosed in a try statement that can catch that exception nor in the body of the method or constructor that "throws" that exception. program code. Note the blue writting is where the error comes from. (Toggle Plain Text) class Database { public int lengthofFile; // holds the file length public String tempString = ""; // holds the added value from main. This value is to be added to the list public String oldFile [] = new String [1]; // this will hold the old file public String newFile [] = new String [1]; // this will hold the updated file public BufferedReader input2; // the contructor. When an object is created this is the default method used. public Database () { // before we can modify the file we need to know how many lines it is, at the moment. input2 = new BufferedReader (new FileReader ("C:\\output.txt")); lengthofFile = Integer.valueOf (input2.readLine ()).intValue (); try { c.print ("I'm in Try"); } catch (IOException input2) { c.println ("Input error"); /* sets the length of the file sothatwecanmodify it later on/ oldFile = new String [lengthofFile]; newFile = new String [lengthofFile + 1]; } } } class Database { public int lengthofFile; // holds the file length public String tempString = ""; // holds the added value from main. This value is to be added to the list public String oldFile [] = new String [1]; // this will hold the old file public String newFile [] = new String [1]; // this will hold the updated file public BufferedReader input2; // the contructor. When an object is created this is the default method used. public Database () { // before we can modify the file we need to know how many lines it is, at the moment. input2 = new BufferedReader (new FileReader ("C:\\output.txt")); lengthofFile = Integer.valueOf (input2.readLine ()).intValue (); try { c.print ("I'm in Try"); } catch (IOException input2) { c.println ("Input error"); / sets the length of the file sothatwecanmodify it later on*/ oldFile = new String [lengthofFile]; newFile = new String [lengthofFile + 1]; } } } __________________ Death smiles at us all. All a man can do is smile back.

Apr 28th, 2006, 11:03 PM	#8
SugarHigh Newbie Join Date: Apr 2006 Location: Metro Detroit Area Posts: 3 Rep Power: 0	ignore this Last edited by SugarHigh; Apr 28th, 2006 at 11:13 PM. Reason: Accidentally sent this prematurely, didn't notice until I finished the post below

Apr 13th, 2006, 3:29 AM	#5
Arevos Programming Guru Join Date: Aug 2005 Location: England Posts: 1,499 Rep Power: 5	Catch "FileNotFoundException".

Apr 28th, 2006, 11:05 PM	#9
SugarHigh Newbie Join Date: Apr 2006 Location: Metro Detroit Area Posts: 3 Rep Power: 0	The problem is that you either have to do a try-catch block that catches an IOException. You must do this for anything that has to do with file IO. Here is what is should look like: (Toggle Plain Text) try{ input2 = new BufferedReader (new FileReader ("C:\\output.txt")); } catch(IOException e){ // other code } try{ input2 = new BufferedReader (new FileReader ("C:\\output.txt")); } catch(IOException e){ // other code } NOTE: If you are trying to do file IO in a method as opposed to a constructor, you can just append "throws IOException" to the method name (Toggle Plain Text) Example: public String exampleMethod(BufferedReader b) throws IOException{ // Code }; Example: public String exampleMethod(BufferedReader b) throws IOException{ // Code }; This way you don't have to use a try-catch block each time you deal with file IO, at least in that method.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode