Java Double Number Round round2(int a, int preserveDigits)

Description

Math#round(double) -like operation for integers preserving the given number of digits in contrary to MathUtil#round(int,int) where cut-of-digits are specified:
return round(a, getDigits(a) - preserveDigits)

License

Open Source License

Parameter

Parameter	Description
a	- a value
preserveDigits	- the number of digits to preserve

Return

the new value

Declaration

public static int round2(int a, int preserveDigits)

Method Source Code

//package com.java2s;
/**//from   ww w  .jav a 2 s. c o  m
 * Syncnapsis Framework - Copyright (c) 2012-2014 ultimate
 * 
 * This program is free software; you can redistribute it and/or modify it under the terms of
 * the GNU General Public License as published by the Free Software Foundation; either version
 * 3 of the License, or any later version.
 * 
 * This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY;
 * without even the implied warranty of MECHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details.
 * 
 * You should have received a copy of the GNU General Plublic License along with this program;
 * if not, see <http://www.gnu.org/licenses/>.
 */

public class Main {
    /**
     * {@link Math#round(double)}-like operation for integers preserving the given number of digits
     * in contrary to {@link MathUtil#round(int, int)} where cut-of-digits are specified:<br>
     * <code>return round(a, getDigits(a) - preserveDigits)</code>
     * 
     * @param a - a value
     * @param preserveDigits - the number of digits to preserve
     * @return the new value
     */
    public static int round2(int a, int preserveDigits) {
        return round(a, getDigits(a) - preserveDigits);
    }

    /**
     * Modification of {@link Math#round(double)} taking an additional argument representing the
     * requested accuracy in the following way:<br>
     * <code>double fac = Math.pow(10, digits);<br>
     * return fac * Math.round(a / fac);</code>
     * 
     * @param a - a value
     * @param cutOfDigits - the number of digits to shift the value before and after rounding
     * @return the new value
     */
    public static double round(double a, int cutOfDigits) {
        double fac = Math.pow(10, cutOfDigits);
        return fac * Math.round(a / fac);
    }

    /**
     * {@link Math#round(double)}-like operation for integers, e.g.:
     * <ul>
     * <li>1234, 3 --> 1000 (like floor, since digits are < 5)</li>
     * <li>1234, 2 --> 1200 (like floor, since digits are < 5)</li>
     * <li>1234, 1 --> 1230 (like floor, since digits are < 5)</li>
     * <li>5678, 3 --> 6000 (like ceil, since digits are >= 5)</li>
     * <li>5678, 2 --> 5700 (like ceil, since digits are >= 5)</li>
     * <li>5678, 1 --> 5680 (like ceil, since digits are >= 5)</li>
     * </ul>
     * Some "unusual" cases:
     * <ul>
     * <li>1234, 5 --> 0 (like floor, since digits are < 5)</li>
     * <li>1234, 4 --> 0 (like floor, since digits are < 5)</li>
     * <li>1234, 0 --> 1234 (like floor, since digits are < 5)</li>
     * <li>1234, -1 --> 1234 (like floor, since digits are < 5)</li>
     * <li>5678, 5 --> 100000 (like ceil, since digits are >= 5)</li>
     * <li>5678, 4 --> 10000 (like ceil, since digits are >= 5)</li>
     * <li>5678, 0 --> 5678 (like ceil, since digits are >= 5)</li>
     * <li>5678, -1 --> 5678 (like ceil, since digits are >= 5)</li>
     * </ul>
     * 
     * @param a - a value
     * @param cutOfDigits - the number of digits to "cut of"
     * @return the new value
     */
    public static int round(int a, int cutOfDigits) {
        if (cutOfDigits <= 0)
            return a;
        int fac = 1;
        while (--cutOfDigits >= 0)
            fac *= 10;
        int ret = (a / fac) * fac;
        if (a - ret > fac / 2)
            ret += fac;
        return ret;
    }

    /**
     * Get the number of digits for the given value
     * 
     * @param a - a value
     * @return the number of digits
     */
    public static int getDigits(int a) {
        int digits = 0;
        while (a != 0) {
            digits++;
            a /= 10;
        }
        return digits;
    }
}