Greetings rejct-ga,
Based on your question, it seems you are looking to get some insight
into how Java writes to a file and reads files.
WRITING TO A FILE
// Begin sample file writing code
import java.io.FileWriter;
import java.io.PrintWriter;
// creates a FileWriter object that will write to filename.txt
// second parameter is a boolean that will append new values to the
file
FileWriter fw = new FileWriter("filename.txt", true);
// PrintWriter uses the FileWriter object to output data
PrintWriter pw = new PrintWriter(fw);
// writing a value to file on a new line
int myValue = 432;
pw.println(myValue);
// End sample code
READING FROM A FILE
// Begin sample file writing code
import java.io.FileReader;
import java.io.BufferedReader;
// creates a FileReader object that reads from filename.txt
FileReader fr = new FileReader("filename.txt");
// BufferedReader uses FileReader to retrieve file contents
BufferedReader br = new BufferedReader(fr);
// reads in the next line from the file
String lineOne = br.readLine();
// converts the String to an int
try
{
int lineOneIntValue = Integer.parseInt(lineOne);
}
catch(NumberFormatException n)
{
System.out.println("NumberFormatException: " + n.getMessage());
}
// end sample code
Of course the code snippets above just exhibit how these I/O classes
can be used for simple read and write operations with files, but you
can get into some pretty obscure things if you need to :)
You can read more about the IO classes used in the sample at the Java
Sun site:
http://java.sun.com/j2se/1.3/docs/api/java/io/FileWriter.html
http://java.sun.com/j2se/1.3/docs/api/java/io/PrintWriter.html
http://java.sun.com/j2se/1.3/docs/api/java/io/FileReader.html
http://java.sun.com/j2se/1.3/docs/api/java/io/BufferedReader.html
If you have any problems understanding the information above please do
post a clarification and I will respond promptly.
Cheers!
answerguru-ga |
Request for Answer Clarification by
rejct-ga
on
12 Jun 2003 12:49 PDT
i want to read 10,000 random numbers to a text file how would i do
that
when i create the file writer it throws back a null page...
what i want is to convert the out-put of this code to a text file:
im using Sun j2sdk1.4.1 and running it through DOS. what i cant figure
out how to do is to save the output to a .txt file, when i want
another program to read the data and place it into an array
import java.math.*;
public class RandomIntegerGenerator{
int min = 0;
int max = 5;
int numberToGenerate = 5;
public static void main(String[] args){
RandomIntegerGenerator generator = new
RandomIntegerGenerator();
int[] uniqueIntegers = generator.generate();
System.out.println("5");
for (int i = 0; i < uniqueIntegers.length; i++){
System.out.println(uniqueIntegers[i]);
}
}
public int getMinimum(){
return min;
}
public int getMaximum(){
return max;
}
public int getNumberToGenerate(){
return numberToGenerate;
}
public void setMinimum(int min){
this.min = min;
}
public void setMaximum(int max){
this.max = max;
}
public void setNumberToGenerate(int numberToGenerate){
this.numberToGenerate = numberToGenerate;
}
public int[] generate(){
int[] numbers = new int[getNumberToGenerate()];
for (int i = 0; i < numbers.length; i++){
boolean uniqueNewIntegerFound = false;
int newInteger = min -1;
while (!uniqueNewIntegerFound){
newInteger = getRandomInteger();
boolean isUsed = false;
for (int j = 0;j <= i; j++){
if (numbers[j] == newInteger) isUsed = true;
}
if (!isUsed) {
uniqueNewIntegerFound = true;
numbers[i] = newInteger;
}
}
}
return numbers;
}
private int getRandomInteger(){
double randomNumber = Math.random();
randomNumber = randomNumber * (double)(max - min + 1);
return (int)randomNumber;
}
}
|
Clarification of Answer by
answerguru-ga
on
12 Jun 2003 13:21 PDT
Hi again,
I believe I missed two lines for the writer section:
fw.close();
pw.close();
This line closes the file, so your changes in the program will be
reflected appropriately.
From the code you provided, I have added the writing function (only
the main method needs updating based on what you have provided:
// need to add import of IO package
import java.io.*;
// modified main method
public static void main(String[] args)
{
RandomIntegerGenerator generator = new
RandomIntegerGenerator();
FileWriter fw = new FileWriter("output.txt");
PrintWriter pw = new PrintWriter(fw);
int[] uniqueIntegers = generator.generate();
pw.println("5");
for (int i = 0; i < uniqueIntegers.length; i++)
{
pw.println(uniqueIntegers[i]);
}
fw.close();
pw.close();
}
This code above will create a new file, output.txt, then prints the
value "5" on the first line followed by values taken from the int[] on
subsequent lines.
When you are reading back the data from the file, use the sample code
from the READER section in the original answer.
Hope that helps,
answerguru-ga
|
Request for Answer Clarification by
rejct-ga
on
12 Jun 2003 13:37 PDT
also the reader sample reads the first line, how would i read the other lines
|
Clarification of Answer by
answerguru-ga
on
12 Jun 2003 14:19 PDT
You just need to keep calling br.readLine() where appropriate and
retrieving the String that is returned. The class keeps track of where
you are in the file and just moves down one line each time. At the
last line you will retrieve a null value, which will tell you that you
have reached the end of the file.
It seems that for your purpose a loop would do the trick :)
answerguru-ga
|
Request for Answer Clarification by
rejct-ga
on
12 Jun 2003 15:41 PDT
in the main section i am getting errors... any ideas on how to correct the problem
C:\WINDOWS>cd c:\java
C:\java>c:\sdk\bin\javac RandomIntegerGenerator.java
RandomIntegerGenerator.java:24: unreported exception java.io.IOException; must b
e caught or declared to be thrown
FileWriter fw = new FileWriter("output.txt");
^
RandomIntegerGenerator.java:36: unreported exception java.io.IOException; must b
e caught or declared to be thrown
fw.close();
^
2 errors
C:\java>
|
Clarification of Answer by
answerguru-ga
on
12 Jun 2003 15:47 PDT
Yes, you need to surround all of the code in your main by a try/catch block:
try
{
// all your code here
}
catch(IOException io){}
|
