CountRandoms.java

import java.io.File;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.Random;

// generate random integers and report their frequencies of occurrence
public class CountRandoms
{
    public static void main (String[] args) {
        // random integers will be generated in the range [1, biggest]
        int biggest = 10;
        // how many random values to generate
        int howMany = 1000;
        // filename to which to write report
        String rptFile = "countRandomsRpt.txt";

        // generate the vales and write the report
        saveReport(
            getCountsReport(
                getFrequency(
                    biggest,
                    getRandoms( biggest, howMany )
                )
            ),
            rptFile
        );
    }

    // generate howMany random integers in the range [1, biggest]
    public static int[] getRandoms( int biggest, int howMany ) {
        // allocate array to hold random integers
        int[] r = new int[ howMany ];
        // create new Random object
        Random rand = new Random();
        // load new, random integer in range [1, biggest] to array
        for (int i = 0; i < howMany; i++) {
            r[ i ] = 1 + rand.nextInt( biggest );
        }
        return r;
    }
    // count the frequency of occurrence of each integer in the
    // range [1, biggest] in the array r
    public static int[] getFrequency( int biggest, int[] r ) {
        // allocate array to hold frequency count for each integer
        // in the range [1, biggest]
        int[] freq = new int[ biggest ];
        for (int i = 0; i < r.length; i++) {
            freq[ r[ i ] - 1 ]++;
        }
        return freq;
    }
    // compose a report of freq(uency) counts
    public static String getCountsReport( int[] freq ) {
        // total up the frequencies and identify the number of digits
        // in the largest frequency
        int maxFWidth =  0;
        int howMany = 0;
        for (int i = 0; i < freq.length; i++) {
            howMany += freq[ i ];
            maxFWidth = Math.max(maxFWidth, freq[ i ]);
        }
        maxFWidth = ("" + maxFWidth).length();
        // number of digits in biggest value
        int maxNWidth = ("" + freq.length).length();
        // collect report output
        StringBuffer rpt = new StringBuffer();
        // add report headings
        rpt.append(
            "Random Number Frequency Counts Report\n" +
            "-------------------------------------\n" +
            "For " + howMany +" random integer in the range [1, " +
            freq.length + "]:\n\n"
        );
        // add frequency detail for each number
        for (int i = 0; i < freq.length; i++) {
            rpt.append(
                "   " + padLeft( maxNWidth, i + 1) + " occurred " +
                padLeft( maxFWidth, freq[ i ] ) + " times\n"
            );
        }
        return rpt.toString();
    }
    // write report string rpt to file named rptFile
    public static void saveReport( String rpt, String rptFile ) {
        // allocate report file and stream for writing
        File outfile = new File( rptFile );
        FileOutputStream out = null;
        try { out = new FileOutputStream( outfile ); }
        catch ( FileNotFoundException e ) {
            // probably should do something more useful
            System.out.println( "Error!!! File Not Found\n" + e.toString() );
        }
        try { out.write( rpt.getBytes() ); }
        catch ( IOException e ){
            // probably should do something more useful
            System.out.println(
                "reportCounts() failed trying to write a record to " +
                rptFile + "\n" + e.toString()
            );
        }
        try { out.close();   }
        catch (IOException e) {
            // probably should do something more useful
            System.out.println(
                "reportCounts() failed trying to close " +
                rptFile + "\n" + e.toString()
            );
        }
    }
    // convert an int to string of given width, padded with blanks on
    // the left-hand side
    public static String padLeft( int width, int n) {
        String p = "" + n;
        while ( width > p.length() ) {
            p = " " + p;
        }
        return p;
    }
}