DataInputStream

[marks20101]

The following code takes the contents of one file and copies it to another file.
How can I read the Ints from one file, add 10 to each int and put the results into another file as text?

import java.io.*;

public class Copy {
public static void main(String[] args) throws IOException {

FileInputStream inputFile = new FileInputStream("theints.txt");
DataInputStream in = new DataInputStream(inputFile);

FileOutputStream outputFile = new FileOutputStream("outagain.txt");
DataOutputStream out = new DataOutputStream(outputFile);
int c;


while ((c = in.read()) != -1)
out.write(c);



in.close();
out.close();
}
}

[sjalle]

Use BufferedReader/BufferedWriter instead of DataInputStream for this.
The readInt() method of DataInputStream reads four bytes from the file
and interprets that as a four byte int, I don't think that is a format suited
for your .txt file.

    BufferedReader br=new BufferedReader(new FileReader("c:\\tmp\\theints.txt"));
    BufferedWriter bw=new BufferedWriter(new FileWriter("c:\\tmp\\outagain.txt"));
    String line=null;

    while ( (line = br.readLine()) != null) {
      String[] intStr = line.split(" "); // if ints are separated by space
      String outLine = "";
      for (int i = 0; i < intStr.length; i++) {
        int n = Integer.parseInt(intStr[i]);
        outLine += (n + 10) + " ";
      }
      bw.write(outLine);
      bw.newLine();
    }

    br.close();
    bw.close();

[marks20101]

Thanks for the response. Good point on using the BufferReader. The program comples fine, but I get a runtime error(numberformatexception)... on line....
int n = Integer.parseInt(intStr[i]);?

Seems like it does not want to parse the elements in the array to ints?

Thanks....

[sjalle]

Integer.parseInt(String s) throws numberFormatException when the contents of
s is not a stringrepresentation of an int. I have tested the code on an input file like this:

3 1 2
1 1 1 -1
2 2 2 2
3 3 3 3
4 4 4 4
5 5 5 5
6 6 6 6
7 7 7 7
8 8 8 8
0

Remember, if the string has leading or trailing blanks. the parse fails, so a safe way is: Integer.parseInt(s.trim())

[marks20101]

I'm still getting that format error?
Here is what I have...and used the data from your example.


BufferedReader br=new BufferedReader(new FileReader("intString.txt"));
BufferedWriter bw=new BufferedWriter(new FileWriter("outagain.txt"));
String line=null;

while ( (line = br.readLine()) != null) {
String[] intStr = line.split(" "); // if ints are separated by space
String outLine = "";
for (int i = 0; i < intStr.length; i++) {
String s=intStr[i];
int n = Integer.parseInt(s.trim()); <<points to this line?
outLine += (n + 10) + " ";


bw.write(outLine);
bw.newLine();
...........................
not sure if I have the trim set up right, or what I'm not processing?
Thanks again...

[sjalle]

I strongly suspect that the stringsplit yields other stuff than just integer
strings. The trim() is not required in this case, since a split(" ") cannot yield
strings w. leading or trailing blanks as the blank is the split delimiter.

You should enclose the process in a try-catch to see what is happening:

BufferedReader br=new BufferedReader(new FileReader("intString.txt"));
BufferedWriter bw=new BufferedWriter(new FileWriter("outagain.txt"));
String line=null;

while ( (line = br.readLine()) != null) {
  String[] intStr = line.split(" "); // if ints are separated by space
  String outLine = "";
  int n;
  for (int i = 0; i < intStr.length; i++) {
    String s=intStr[i];
    try { 
       n = Integer.parseInt(s); 
    } catch (NumberFormatException nfe) {
       System.out.println("the line: ["+line+"] failed integer conversion");
       System.out.println("Failure for :["+intStr[i]+"]");
       System.out.println(nfe.getMessage());
       System.out.println("Element was skipped");
       continue;
    }
    outLine += (n + 10) + " ";
    bw.write(outLine);
    bw.newLine();
  }
}

Also remember that parseInt(String s) fails for float and double values
(values w. a decimal point).