FileInputStream is not ending in java

Question

I was practicing using byte streams in Java when I came across this code:

import java.io.*;
public class CopyBytes_practice {
public static void main(String args[]) throws IOException {
    FileInputStream f=null;
    FileOutputStream fo=null;
    int c;
    int d;
    try {
        f=new FileInputStream("a.png");
        fo=new FileOutputStream("b.png");
        c=f.read();
        while(c != -1){
            fo.write(c);
        }
    } finally {
        if (f != null) {
            f.close();
        }
        if (fo != null) {
            fo.close();
        }
    }
}

I used a 35kb a.png file and a 0kb b.png file to execute the code, but the code ran forever - the size of b.png reached 905mb before I stopped the JVM manually.

I am confused, why is the end of file status not returned? Is it not supported in Binary files, or is something else wrong?

Elliott Frisch · Accepted Answer · 2013-12-10 17:30:28Z

4

You missed something important

c=f.read(); // <-- Read in one byte ...
while(c != -1){
  fo.write(c);
  c=f.read(); // <--- Add this, to Read in the next byte (or -1)...
}

So you were infinitely looping, and writing the first byte from your source.

edited Dec 10, 2013 at 17:30

answered Dec 10, 2013 at 17:07

Elliott Frisch

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3 Comments

user2869389 Over a year ago

That solved it... but i don't get it, can you please explain what c=f.read(); did???

Joao Guilherme Over a year ago

You were reading only the first byte of your source file and writing it forever. It'd never be "-1" so it wouldn't ever stop. Calling c=f.read keeps going further on the source file till its end.

user2869389 Over a year ago

ohk, i get it now, that means writing while((c=f.read()) != -1) could have made my day, ryt? thanks :)

Sleiman Jneidi · Accepted Answer · 2013-12-15 01:33:21Z

4

Yes, because it's an infinite loop, you need to tell the loop where to stop.In other words, the loop should keep reading until it reaches the end of the file.

 while ((c= f.read()) != -1){
    fo.write(c);
 }

edited Dec 15, 2013 at 1:33

answered Dec 10, 2013 at 17:08

Sleiman Jneidi

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1 Comment

Sleiman Jneidi Over a year ago

because c was still equal to the first byte value, read() returns -1 when it reaches the end of the file. Every time you call read(), it jumps to the next chunk @user2869389

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