Date Time Class for Java

DateTime.java

package util;

import java.util.Calendar;


/**
 * Created by rupak on 10/14/15.
 * Use: DateTime.getDate().ToDateTime()
 * Explore static methods
 */
 
public class DateTime{

    private int _yr=0, _mon=0,_day=0, _hr=0, _min=0, _sec=0;
    private String _format="yyyy/mm/dd hh:min:sec";
    private String _format_date="yyyy/mm/dd";
    private String _format_time="hh:min:dd";

    public String ToString(String format){
        return  format.replace("yyyy", String.valueOf(_yr))
                .replace("mm", String.valueOf(_mon))
                .replace("dd", String.valueOf(_day))
                .replace("hh", String.valueOf(_hr))
                .replace("min", String.valueOf(_min))
                .replace("sec", String.valueOf(_sec));
    }


    public String ToString(){
        return  _format.replace("yyyy", String.valueOf(_yr))
                .replace("mm", String.valueOf(_mon))
                .replace("dd", String.valueOf(_day))
                .replace("hh", String.valueOf(_hr))
                .replace("min", String.valueOf(_min))
                .replace("sec", String.valueOf(_sec));
    }

    public String ToDateTime(){
        return  _format.replace("yyyy", String.valueOf(_yr))
                .replace("mm", String.valueOf(_mon))
                .replace("dd", String.valueOf(_day))
                .replace("hh", String.valueOf(_hr))
                .replace("min", String.valueOf(_min))
                .replace("sec", String.valueOf(_sec));
    }

    public String ToDate(String format){
        return  _format_date.replace("yyyy", String.valueOf(_yr))
                .replace("mm", String.valueOf(_mon))
                .replace("dd", String.valueOf(_day)) ;
    }

    public String ToTime(){
        return  _format_time.replace("hh", String.valueOf(_yr))
                .replace("min", String.valueOf(_mon))
                .replace("sec", String.valueOf(_day));
    }

    public static DateTime getDate(){
        Calendar cal = Calendar.getInstance();
        DateTime dateTime = new DateTime();
        dateTime._yr = cal.get(Calendar.YEAR);
        dateTime._mon= cal.get(Calendar.MONTH);
        dateTime._day = cal.get(Calendar.DAY_OF_MONTH);
        dateTime._hr= cal.get(Calendar.HOUR_OF_DAY);
        dateTime._min= cal.get(Calendar.MINUTE);
        dateTime._sec= cal.get(Calendar.SECOND);
        return  dateTime;
    }
}

how do I use the class Calendar to print odds and even weekdays from a period of time of a years?