Java File I/O Example

import java.util.*;     // for Scanner class and a few other useful things
import java.io.*;       // to enable reading and writing from files

public class FileIOExample {

    /* you need to include the "throws IOException" declaration
     * because things may go wrong with the file I/O process
     *
     * unless you want to use try-catch statements
     */
    public static void main(String[] args) throws IOException {

        // this line opens a Scanner to read from your input file
        // it reads just as if you were typing things into the console
        Scanner input = new Scanner(new File("input.txt"));

        // this next line creates a file and allows you to print to it
        // you use it like System.out.println()
        PrintWriter out = new PrintWriter(new File("output.txt"));

        // for instance, if you want to read in a list of integers from a file...
        List<Integer> list = new ArrayList<Integer>();
        while (input.hasNextInt()) {
            list.add(input.nextInt());
        }

        // then, if you want to sort the numbers and print it back out to your file...
        Collections.sort(list);
        for (Integer i : list) {
            out.println(i);     // just like printing to console...! without the System
        }

        /* THESE NEXT TWO LINES ARE IMPORTANT... since you opened two files, one for reading and
         * one for writing, you have to close those files so that it releases the resources
         * back to your computer
         */
        input.close();
        out.close();
    }

}