Binary I/O Classes (Summing all the integers in a binary data file)

Question

Could someone please help me through this problem? I'm not really good with the binary I/O classes.

Suppose a binary data file named Exercise 13b_1.dat has been created using writeInt(int) in DataOutputStream. The file contains an unspecified number of integers. Write a program to find the sum of integers.

Programming is mostly playing with binary, and you have all the time in the world. So try something, and ask about details that are unclear to you. — ruslik, Dec 03 '10 at 01:29
Hint: what method do you think would be used to read things that were written with a method called "writeInt"? — Laurence Gonsalves, Dec 03 '10 at 01:43

score 0 · Answer 1 · edited Nov 19 '12 at 00:55

0

Here is a simple solution.

FileInputStream fis = new FileInputStream("13b_1.dat");
DataInputStream dis = new DataInputStream(fis);
int count = 0;

try {
    while (true) {
        dis.readInt();
        count++;
    }

} catch (EOFException e) {}

System.out.println("There are " + count + " integers.");

For efficiency, you can read in a bunch of bytes and divide the number of bytes by four, since one integer is four bytes.

edited Nov 19 '12 at 00:55

Dan Is Fiddling By Firelight

5,981
17
77
128

answered Dec 03 '10 at 01:42

Xiangdong

254
2
10

Of course, using exceptions for control flow isn't terribly good style. If only there was some way to figure out how many ints are in that file. – Dmitri Dec 03 '10 at 02:47
@Dmitri: If writeInt writes a constant number of bytes for every argument, you could divide the file length by that number to get the number of integers in the file. – Thomas Dec 03 '10 at 18:18
@Thomas: I was using gentle sarcasm to guide the author of the question towards the path to a solution :) – Dmitri Dec 03 '10 at 23:13

Binary I/O Classes (Summing all the integers in a binary data file)

1 Answers1