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How can I read from, and write to, files in Java?

Stand-alone applications written in Java can access the local file-system, but applets executing under the control of a browser cannot. With this in mind, lets take a look at two simple applications that write a line of text to a file, and read it back




كود:
import java.io.*;

public class MyFirstFileWritingApp
{
    // Main method
    public static void main (String args[])
    {
        // Stream to write file
        FileOutputStream fout;        

        try
        {
            // Open an output stream
            fout = new FileOutputStream ("myfile.txt");

            // Print a line of text
            new PrintStream(fout).println ("hello world!");

            // Close our output stream
            fout.close();        
        }
        // Catches any error conditions
        catch (IOException e)
        {
            System.err.println ("Unable to write to file");
            System.exit(-1);
        }
    }    
}

This simple application creates a FileOutputStream, and writes a line of text to the file. You'll notice that the file writing code is enclosed within a try { .... } catch block. If you're unfamiliar with exception handling in Java, this requires a little explanation.
Certain methods in Java have the potential to throw an error condition, known as an exception. We have to trap these error conditions, so we 'catch' any exceptions that may be thrown.
The task of reading from a file is also just as easy. We create a FileInputStream object, read the text, and display it to the user.


كود:
import java.io.*;

public class MyFirstFileReadingApp
{
    // Main method
    public static void main (String args[])
    {
        // Stream to read file
        FileInputStream fin;        

        try
        {
            // Open an input stream
            fin = new FileInputStream ("myfile.txt");

            // Read a line of text
            System.out.println( new DataInputStream(fin).readLine() );

            // Close our input stream
            fin.close();        
        }
        // Catches any error conditions
        catch (IOException e)
        {
            System.err.println ("Unable to read from file");
            System.exit(-1);
        }
    }    

}