RoundTest.java

import java.text.DecimalFormat;
import java.util.Scanner;

class RoundTest {

    /**
    *   Program:    RoundTest.java
    *   Purpose:    Compare unformatted, formatted and rounded numbers
    *   Creator:    Chris Clarke
    *   Created:    29.05.2014
    *   Note:       Using DecimalFormat, it only goes up to 1.9, NOT 2.0!! So beware!!
    */

    public static void main(String []args) {

        DecimalFormat df = new DecimalFormat("0.0");
        Scanner in = new Scanner(System.in);
        String s = "";
        double a;

        for (int i=0; i<3; i++) {
            System.out.println("Press enter to continue...");
            s = in.nextLine();

            System.out.printf("Test %d%n", (i+1));
            switch (i) {
                case 0: System.out.println( "Without formatting:");
                    for (a=0.0; a<=2.0; a+=0.1) {
                        System.out.println(a);
                    } // end for a
                    break;
                case 1: System.out.println( "Using DecimalFormat:");
                    for (a=0.0; a<=2.0; a+=0.1) {
                        System.out.println( df.format(a));
                    } // end for
                    break;
                case 2: // the best way to display numbers
                    System.out.println( "Using round() method:");
                    for (a=0.0; a<=2.0; a+=0.1) {
                        // round to 1 decimal place
                        a = round(a, 1);
                        System.out.println(a);
                    } // end for
                    break;
            } // end switch
        } // end for i
    } // end main()

    // round d to p decimal places
    public static double round(double d, int p) {
        double n = Math.pow(10, p); // 10 ^ p
        d *= n;
        d = Math.round(d); // round to nearest int
        d /= n;
        return d;
    } // end function round()

} // end class RoundTest