Submission for Easy Challenge #118

ReplaceApp.java

import java.util.Calendar;
import java.util.HashMap;
import java.util.Map;
import java.util.Map.Entry;

interface DateTimeComponent {
    public String write(final Calendar calendar);
}

class Year implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.YEAR));
    }
}

class Month implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        int monthValue = calendar.get(Calendar.MONTH);
        String monthString;
        switch(monthValue) {
            case Calendar.JANUARY:
                monthString = "1";
                break;
            case Calendar.FEBRUARY:
                monthString = "2";
                break;
            case Calendar.MARCH:
                monthString = "3";
                break;
            case Calendar.APRIL:
                monthString = "4";
                break;
            case Calendar.MAY:
                monthString = "5";
                break;
            case Calendar.JUNE:
                monthString = "6";
                break;
            case Calendar.JULY:
                monthString = "7";
                break;
            case Calendar.AUGUST:
                monthString = "8";
                break;
            case Calendar.SEPTEMBER:
                monthString = "9";
                break;
            case Calendar.OCTOBER:
                monthString = "10";
                break;
            case Calendar.NOVEMBER:
                monthString = "11";
                break;
            case Calendar.DECEMBER:
                monthString = "12";
                break;
            default:
                monthString = "";
                    
        }
        return monthString;
    }
}

class Day implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.DAY_OF_MONTH));
    }
}

class Hour12 implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        int hourValue = calendar.get(Calendar.HOUR);
        return String.valueOf(hourValue == 0 ? 12 : hourValue);
    }
}

class Hour24 implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.HOUR_OF_DAY));
    }
}

class Minute implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.MINUTE));
    }
}

class Second implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.SECOND));
    }
}

class Millisecond implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        return String.valueOf(calendar.get(Calendar.MILLISECOND));
    }
}

class AMPM implements DateTimeComponent {
    @Override
    public String write(final Calendar calendar) {
        int AMPMValue = calendar.get(Calendar.AM_PM);
        String AMPMString = "";
        
        switch(AMPMValue) {
            case Calendar.AM:
                AMPMString = "AM";
                break;
            case Calendar.PM:
                AMPMString = "PM";
                break;
        }
        
        return AMPMString;
    }
}
class Replacer {
    
    private Map<String,DateTimeComponent> replacements;
    
    public Replacer(Map<String,DateTimeComponent> replacementsInit) {
        replacements = replacementsInit;
    }
    
    public String replace(String string, Calendar calendar) {
        for(Entry<String,DateTimeComponent> replacmentPair : 
                replacements.entrySet()) {
            string = string.replace(replacmentPair.getKey(),
                    replacmentPair.getValue().write(calendar));
        }
        return string;
    }
}

public class ReplaceApp {
    public static void main(String[] args) {
        Map<String,DateTimeComponent> replacements = new HashMap<>();
        replacements.put("%l", new Millisecond());
        replacements.put("%s", new Second());
        replacements.put("%m", new Minute());
        replacements.put("%h", new Hour12());
        replacements.put("%H", new Hour24());
        replacements.put("%d", new Day());
        replacements.put("%M", new Month());
        replacements.put("%y", new Year());
        replacements.put("%c", new AMPM());
        
        Replacer replacer = new Replacer(replacements);
        
        // Tests
        Calendar calendarNow = Calendar.getInstance();
        String[] testStrings = {
            "%s.%l",
            "%s:%m:%h %M/%d/%y",
            "The minute is %m! The hour is %h.",
            "24 hour time: %H:%m:%s.%l",
            "12 hour time: %h:%m:%s.%l %c"
        };
        
        for(String testString : testStrings) {
            System.out.println(replacer.replace(testString, calendarNow));
        }
        
    }
}