How to write file in java?

Question

I am facing file write issue ,Actually when i run this below code the while loop iterate infinite times.

package com.demo.io;

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

public class CopyFile {

    public static void main(String[] args) {

        FileInputStream in = null;
        FileOutputStream out = null;
        try {
            in = new FileInputStream("C:/Users/s.swain/Desktop/loginissue.txt");
            out = new FileOutputStream("C:/Users/s.swain/Desktop/output.txt");
            int c = in.read();
            while (c != -1) {
                System.out.println(c);
                out.write(c);
            }

        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (in != null) {
                try {
                    in.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
            if (out != null) {
                try {
                    out.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }
    }
}

Anyone can tell me how to write this file.

Thanks

Sitansu

I'd suggest using Apache Commons IO's IOUtils.copy(InputStream, OutputStream. — Thomas
– Thomas, Commented May 18, 2015 at 12:08
Although all answers just suggest to fix the bug in your code; I second the suggestion from Thomas: unless this is for homework/learning; you should not reinvent the wheel. There are libraries that do "file copy" for you; and most likely they are much better tested and will deal with many "cross-plattform" issues that you will not think of. — GhostCat
– GhostCat, Commented May 18, 2015 at 12:11
or Files.copy(Paths.get("pathToInputFile"), Paths.get("pathToOutputFile")); — griFlo
– griFlo, Commented May 18, 2015 at 12:12

Jordi Castilla · Accepted Answer · 2015-05-18 12:13:30Z

3

This conditions remains true for eternity true because you never update c in the while-loop:

while (c != -1) {

Use in.read inside while-loop!

int c = in.read();
while (c != -1) {
    System.out.println(c);
    out.write(c);
    c = in.read();
}

edited May 18, 2015 at 12:13

answered May 18, 2015 at 12:09

Jordi Castilla

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1 Comment

Stultuske Over a year ago

I assume you meant: this condition remains true for eternity, once it becomes true.

score 3 · Accepted Answer · 2015-05-18 12:17:48Z

3

You missed to read the next byte:

int c = in.read();
while (c != -1) {
    System.out.println(c);
    out.write(c);
    c = in.read();//this line added to read next byte
}

Or, you can simply use:

int c;
while (-1 != (c = in.read())) { /* condition with assignment */
    out.write(c);
}

edited May 18, 2015 at 12:17

answered May 18, 2015 at 12:09

user2575725

Comments

QBrute · Accepted Answer · 2015-05-18 12:09:12Z

2

You only read c once. Update your while-loop to

while (c != -1) {
    System.out.println(c);
    out.write(c);
    c = in.read();
}

answered May 18, 2015 at 12:09

QBrute

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Comments

Ajay Chaudhary · Accepted Answer · 2015-05-18 12:15:44Z

1

Just do this

int c = 0;
 while ((c = in.read()) != -1) {
 System.out.println((char)c);
 out.write((byte)c);
 }

answered May 18, 2015 at 12:15

Ajay Chaudhary

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Comments

tim · Accepted Answer · 2015-05-18 12:20:23Z

1

Try something like this:

        while(c != null){
            System.out.println(c);
            out.write(c);
            c = reader.readLine();
        }

edited May 18, 2015 at 12:20

answered May 18, 2015 at 12:11

tim

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Comments

Stultuske · Accepted Answer · 2015-05-18 12:08:54Z

0

while (c != -1) {
                System.out.println(c);
                out.write(c);
            }

what do you think will happen here, if c != -1 ? You don't update the value of c, so it will cause an infinite loop.

answered May 18, 2015 at 12:08

Stultuske

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