Is there an -1 at the end of an Inputstream?

Question

I am quite new to programming.

While reading the article Byte Streams in "Basic I/O" in The Java Tutorials by Oracle, I came accross this code:

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;

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

        FileInputStream in = null;
        FileOutputStream out = null;

        try {
            in = new FileInputStream("xanadu.txt");
            out = new FileOutputStream("outagain.txt");
            int c;

            while ((c = in.read()) != -1) {
                out.write(c);
            }
        } finally {
            if (in != null) {
                in.close();
            }
            if (out != null) {
                out.close();
            }
        }
    }
}

I do not understand the condition of the while-loop. Is -1 some kind of sign that the Message is over? Does the FileOutputStream add it at the end?

Thank you all for your attention. I hope you have a wonderfull sylvester.

See [docs](https://docs.oracle.com/javase/8/docs/api/java/io/InputStream.html#read--) — "-1 if the end of the stream is reached" — khelwood, Dec 30 '20 at 16:17
What's a 'sylvester', by the way? This is not a common expression in English. 'New Year', perhaps? — a guest, Dec 30 '20 at 16:34
@aguest It is the last day of the year, and it is spelled Silvester. — Henry, Dec 30 '20 at 16:37
Yes, I meant new year. Its "Silvester" in my mothertongue and I thought it is the same in English, because it is the name of a Saint and names do not change that much between languages. — Auri, Dec 30 '20 at 16:39
Much to my surprise, (secular) New Year's Eve in Israel is also "Silvester's Day". Apparently his birthday was December 31. — Frank Yellin, Dec 30 '20 at 16:52

score 2 · Answer 1 · answered Dec 30 '20 at 16:32

To add to the other answers, the tool for figuring this out is the documentation.

For the 'read' method of FileInputStream:

public int read()
throws IOException

Reads a byte of data from this input stream. This method blocks if no input is yet available. Specified by: read in class InputStream

Returns: the next byte of data, or -1 if the end of the file is reached.

This is definitive.

All standard Java classes are documented in this manner. In case of uncertainty, a quick check will reassure you.

Devi Khositashvili · Answer 2 · 2020-12-30T16:49:37.937

-3

EDIT: "Signals that an end of file or end of stream has been reached unexpectedly during input. This exception is mainly used by data input streams, which generally expect a binary file in a specific format, and for which an end of stream is an unusual condition. Most other input streams return a special value on end of stream."

The right way is to catch EOFException to find out is it end of file or not, but in tihs case reading chars as EOF -1 is returned and not null, and it's working because there is no char for negative ascii, it's the same to check while ((c = in.read()) >= 0) {}, so you can use != -1 and it will work.

edited Dec 30 '20 at 16:49

answered Dec 30 '20 at 16:23

Devi Khositashvili

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1
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1

There is no `EOFException` thrown to catch. – Progman Dec 30 '20 at 16:26
if you write while(true) { in.read() }, after eof you will have exception... don't you agree? – Devi Khositashvili Dec 30 '20 at 16:29
1

It does not, it simply returns `-1`. – Progman Dec 30 '20 at 16:34
What you read from an input stream are bytes, not ASCII characters. – Henry Dec 30 '20 at 16:34
i mean if you read in wile true condition after reading -1, the next read will throw an exception - y it returns -1 in eof but if you don't check it will pass... – Devi Khositashvili Dec 30 '20 at 16:37
1

@DeviKhositashvili It will keep returning `-1` to indicate the end of the file, but it will not throw an `EOFException`. – Progman Dec 30 '20 at 16:39
if you mean only this case, when chars are read, yes - you're right, but in general, you need to catch exception - ill edit to make it more clear. – Devi Khositashvili Dec 30 '20 at 16:48

Is there an -1 at the end of an Inputstream?

2 Answers2