Simple counter

Question

I am trying to read a number from a dat file, add 1 and then write back to the file.
I have tried it with straight read method and readInt and I either get the wrong numbers returned(read) or null(readInt).
Where am I going wrong?
I have cut and pasted many Forum solutions and tried them but I can't seem to get them working either (usually io or type errors when compiling.)
Please help.
// Number Counter
import java.io.*;
public class Counter{
public static void main(String argv[]){
int nis;
try{   
FileInputStream num= new FileInputStream("dnum.dat");
DataInputStream dn = new DataInputStream(num);
System.out.println(dn.read());
int incnum = dn.read();
     int newnum = incnum + 1;
FileOutputStream numout = new FileOutputStream("dnum.dat");
DataOutputStream dos = new DataOutputStream(numout);
dos.write(newnum);
catch(IOException e){System.out.println(e.getMessage());}
}

Answer 1

Hi there,
1.In your code you are reading a byte to be printed and then another one to be edited. So only the second one is changed.
2. With read yout get an int and not the char you want to see.
3. The "int nis" is not needed.
import java.io.*;
public class Counter
  public static void main(String argv[])
    try
      FileInputStream num= new FileInputStream("dnum.dat");
      DataInputStream dn = new DataInputStream(num);
      int incnum = dn.read();
      System.out.println((char)incnum);
      dn.close();
      int newnum = incnum + 1;
      FileOutputStream numout = new FileOutputStream("dnum.dat");
      DataOutputStream dos = new DataOutputStream(numout);
      dos.write(newnum);
      dos.close();
    catch(IOException e){System.out.println(e.getMessage());}
  } Hope that helped.