Sort months ( with strings ) algorithm

Question

I have this months array:

[\"January\", \"March\", \"December\" , \"October\" ]

And I want to have it sorted like this:

[\"         


        

Answer 1

Colleagues,

I see the issue/business problem lasts more than 2 year. I decided to write comparator for sorting months' names (stored as strings) properly. It also holds names of the months for desired locale ============== Comparator =======================

import java.text.SimpleDateFormat;
import java.util.ArrayList;
import java.util.Calendar;

import java.util.Comparator;
import java.util.HashMap;
import java.util.List;
import java.util.Locale;
import java.util.Map;

/**
 *
 * @author akashtalyan
 */
public class MonthNamesComparator implements Comparator {

    private static Map monthMap = new HashMap();
    private final Locale locale;

    public MonthNamesComparator(Locale locale) {
        if (locale == null) {

            throw new NullPointerException("MonthNamesComparator cannot accept null value for Locale parameter.");
        }
        List months = new ArrayList(12);
        Calendar cal = Calendar.getInstance(locale);
        SimpleDateFormat dateFormat = new SimpleDateFormat("MMMM", locale);
        this.locale = locale;
        if (!monthMap.containsKey(locale)) {
            for (int i = 0; i < 12; i++) {
                cal.set(Calendar.MONTH, i);
                months.add(dateFormat.format(cal.getTime()).toLowerCase());
            }
            monthMap.put(locale , months);
        }
    }

    @Override
    public int compare(Object month1, Object month2) {
        List months = monthMap.get(this.locale);
        if (months == null) {
            throw new NullPointerException("MonthNamesComparator cannot perform comparison - internal data is not initialized properly.");
        }
        return (months.indexOf(((String) month1).toLowerCase()) - months.indexOf(((String) month2).toLowerCase()));

    }
}

And simple test class to POC:

import java.util.Locale;
import java.util.Map;
import java.util.Set;
import java.util.TreeMap;

/**
 *
 * @author akashtalyan
 */
public class TestMonths {
    public static void main(String[] args){
        Locale en = Locale.ENGLISH, ru = new Locale("ru","RU");
        String[] monthsToTestEn = new String[] {"FebRUary", "maY", "sepTember", "january", "december"};
        String[] monthsToTestRu = new String[] {"АпреЛь", "январь", "Март", "Август"};

        Map map = new TreeMap(new MonthNamesComparator(en));
        int i = 0;
        System.out.println("En Map original:");
        for (String month : monthsToTestEn) {
            System.out.print(month + " ");
            map.put(month, new StringBuilder(String.valueOf(++i)).append(" position in source array").toString());
        }
            System.out.println();
            System.out.println("En Map sorted:");
        for (String month : (Set)map.keySet()) {
            System.out.println(month + " " + map.get(month));
        }
        i = 0;
        map = new TreeMap(new MonthNamesComparator(ru));
        System.out.println("Ru Map original:");
        for (String month : monthsToTestRu) {
            System.out.print(month + " ");
            map.put(month, new StringBuilder(String.valueOf(++i)).append(" position in source array").toString());
        }
            System.out.println();
        System.out.println("Ru Map sorted:");
        for (String month : (Set)map.keySet()) {
            System.out.println(month + " " + map.get(month));
        }
    }

}

Enjoy it, works like a charm.