Copying the Contents of One text file to Another in Java

filereader, filewriter, java

Solution

It's `finally`, not `finally()`:

try {
    //...
} catch(IOException e) {
    //...
} finally {
    //...
}

By the way, you have an endless loop there:

int c=fr.read();
while(c!=-1) {
    fw.write(c);
}

You must read the data inside the loop in order to let it finish:

int c=fr.read();
while(c!=-1) {
    fw.write(c);
    c = fr.read();
}

In the `finally` block, your `fr` and `fw` variables can't be found since they're declared in the scope of the `try` block. Declare them outside:

FileReader fr = null;
FileWriter fw = null;
try {
    //...

Now, since they are initialized with `null` value, you must also do a `null` check before closing them:

finally {
    if (fr != null) {
        fr.close();
    }
    if (fw != null) {
        fw.close();
    }
}

And the `close` method on both can throw `IOException` that must be handled as well:

finally {
    if (fr != null) {
        try {
            fr.close();
        } catch(IOException e) {
            //...
        }
    }
    if (fw != null) {
        try {
            fw.close();
        } catch(IOException e) {
            //...
        }
    }
}

In the end, since you don't want to have a lot of code to close a basic stream, just move it into a method that handles a `Closeable` (note that both `FileReader` and `FileWriter` implements this interface):

public static void close(Closeable stream) {
    try {
        if (stream != null) {
            stream.close();
        }
    } catch(IOException e) {
        //...
    }
}

In the end, your code should look like:

import java.io.*;
class FileDemo {
    public static void main(String args[]) {
        FileReader fr = null;
        FileWriter fw = null;
        try {
            fr = new FileReader("1.txt");
            fw = new FileWriter("2.txt");
            int c = fr.read();
            while(c!=-1) {
                fw.write(c);
                c = fr.read();
            }
        } catch(IOException e) {
            e.printStackTrace();
        } finally {
            close(fr);
            close(fw);
        }
    }
    public static void close(Closeable stream) {
        try {
            if (stream != null) {
                stream.close();
            }
        } catch(IOException e) {
            //...
        }
    }
}

Since Java 7, we have `try-with-resources`, so code above could be rewritten like:

import java.io.*;
class FileDemo {
    public static void main(String args[]) {
        //this will close the resources automatically
        //even if an exception rises
        try (FileReader fr = new FileReader("1.txt");
             FileWriter fw = new FileWriter("2.txt")) {
            int c = fr.read();
            while(c!=-1) {
                fw.write(c);
                c = fr.read();
            }
        } catch(IOException e) {
            e.printStackTrace();
        }
    }
}

Problem

I am trying to copy the contents of one text file ("1.txt") which contains 2-3 integer numbers (ex: 1 2 3) to another text file ("2.txt") but I am getting the following error upon compilation ``` import java.io.*; class FileDemo { public static void main(String args[]) { try { FileReader fr=new FileReader("1.txt"); FileWriter fw=new FileWriter("2.txt"); int c=fr.read(); while(c!=-1) { fw.write(c); } } catch(IOException e) { System.out.println(e); } finally() { fr.close(); fw.close(); } } } ``` Command prompt:- ``` C:\Documents and Settings\Salman\Desktop>javac FileDemo.java FileDemo.java:20: error: '{' expected finally() ^ FileDemo.java:20: error: illegal start of expression finally() ^ FileDemo.java:20: error: ';' expected finally() ^ FileDemo.java:27: error: reached end of file while parsing } ^ 4 errors ``` But upon checking the code, I find that the finally() block is properly closed.

Original source