Age implementation in Java

Few days ago I saw a post in StackoverFlow asking for finding date of birth from age in java. I thought that why don't I write a class which can manipulate Age. Here is what I came up with.
This class Age stores age in terms of

• Years
• Months
• Days
• Hours
• Minutes
• Seconds

Followings are the features of this class:

• It returns Age for a given Date
• It is Timezone specific
• It returns age as Seconds, Minutes, Hours, Days, Weeks, Months
• Prints Age in a pretty format
• This class is Serializable, Cloneable and Comparable
• It is written using java.time api

import java.io.Serializable;
import java.text.ParseException;
import java.text.SimpleDateFormat;
import java.time.DateTimeException;
import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneId;
import java.time.ZonedDateTime;
import java.time.temporal.ChronoField;
import java.time.temporal.ChronoUnit;
import java.time.temporal.ValueRange;
import java.util.Date;
import java.util.Objects;

/**
 * The class <code>Age</code> represents the length of time that a person has
 * lived or a thing has existed.
 * 
 * @author TapasB
 */
public class Age implements Serializable, Cloneable, Comparable<Age> {

 private static final long serialVersionUID = 210032925430172448L;

 private long years;
 private long months;
 private long days;
 private long hours;
 private long minutes;
 private long seconds;

 // Private Constructor
 private Age() {

 }

 /**
  * Creates and returns a new instance of <code>Age</code> object.
  * 
  * @author TapasB
  * @return a new instance of <code>Age</code>
  */
 public static Age getDefault() {
  return new Age();
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting the given years.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years) {
  return getDefault().setYears(years);
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting given years and months to it.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @param months
  *            - months to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years, long months) {
  return of(years).setMonths(months);
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting given years, months and days to it.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @param months
  *            - months to set
  * @param days
  *            - days to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years, long months, long days) {
  return of(years, months).setDays(days);
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting given years, months, days and hours to it.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @param months
  *            - months to set
  * @param days
  *            - days to set
  * @param hours
  *            - hours to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years, long months, long days, long hours) {
  return of(years, months, days).setHours(hours);
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting given years, months, days, hours and minutes to it.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @param months
  *            - months to set
  * @param days
  *            - days to set
  * @param hours
  *            - hours to set
  * @param minutes
  *            - minutes to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years, long months, long days, long hours, long minutes) {
  return of(years, months, days, hours).setMinutes(minutes);
 }

 /**
  * Creates and returns a new instance of <code>Age</code> object after
  * setting given years, months, days, hours, minutes and seconds to it.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @param months
  *            - months to set
  * @param days
  *            - days to set
  * @param hours
  *            - hours to set
  * @param minutes
  *            - minutes to set
  * @param seconds
  *            - seconds to set
  * @return a new instance of <code>Age</code>
  */
 public static Age of(long years, long months, long days, long hours, long minutes, long seconds) {
  return of(years, months, days, hours, minutes).setSeconds(seconds);
 }

 /**
  * Calculates and returns an instance <code>Age</code> for the given date
  * string and date pattern. The <code>Age</code> will be calculated with
  * respect to the system default time-zone.
  * 
  * @author TapasB
  * @param date
  *            - the birth date as string
  * @param pattern
  *            - date pattern
  * @return an instance of <code>Age</code>
  * @throws ParseException
  *             if the parsing fails
  */
 public static Age fromDateOfBirth(String date, String pattern) throws ParseException {
  Objects.requireNonNull(date, "date");
  Objects.requireNonNull(pattern, "pattern");
  SimpleDateFormat dateFormat = new SimpleDateFormat(pattern);
  return fromDateOfBirth(dateFormat.parse(date));
 }

 /**
  * Calculates and returns an instance of <code>Age</code> for the given
  * {@link Date}. The <code>Age</code> will be calculated with respect to the
  * system default time-zone.
  * 
  * @author TapasB
  * @param date
  *            - the birth date
  * @return an instance of <code>Age</code>
  */
 public static Age fromDateOfBirth(Date date) {
  Objects.requireNonNull(date, "date");
  return fromDateOfBirth(date, ZoneId.systemDefault());
 }

 /**
  * Calculates and returns an instance of <code>Age</code> for the given
  * {@link Date} with respect to the given {@link ZoneId}.
  * 
  * @author TapasB
  * @param date
  *            - the birth date
  * @param zone
  *            - the zone ID to use
  * @return an instance of <code>Age</code>
  */
 public static Age fromDateOfBirth(Date date, ZoneId zone) {
  Objects.requireNonNull(date, "date");
  Objects.requireNonNull(zone, "zone");
  Instant instant = Instant.ofEpochMilli(date.getTime());
  LocalDateTime dateTime = LocalDateTime.ofInstant(instant, zone);
  return fromDateOfBirth(dateTime, zone);
 }

 /**
  * Calculates and returns an instance of <code>Age</code> for the given
  * {@link LocalDateTime}. The <code>Age</code> will be calculated with
  * respect to the system default time-zone.
  * 
  * @author TapasB
  * @param date
  *            - the birth date
  * @return an instance of <code>Age</code>
  */
 public static Age fromDateOfBirth(LocalDateTime date) {
  Objects.requireNonNull(date, "date");
  return fromDateOfBirth(date, ZoneId.systemDefault());
 }

 /**
  * Calculates and returns an instance of <code>Age</code> for the given
  * {@link LocalDateTime} with respect to the given {@link ZoneId}.
  * 
  * @author TapasB
  * @param date
  *            - the birth date
  * @param zone
  *            - the zone ID to use
  * @return an instance of <code>Age</code>
  */
 public static Age fromDateOfBirth(LocalDateTime date, ZoneId zone) {
  Objects.requireNonNull(date, "date");
  Objects.requireNonNull(zone, "zone");
  ZonedDateTime zonedDate = date.atZone(zone);
  return fromDateOfBirth(zonedDate);
 }

 /**
  * Calculates and returns an instance of <code>Age</code> for the given
  * {@link ZonedDateTime}.
  * 
  * @author TapasB
  * @param date
  *            - the birth date
  * @return an instance of <code>Age</code>
  */
 public static Age fromDateOfBirth(ZonedDateTime date) {
  Objects.requireNonNull(date, "date");
  ZonedDateTime now = ZonedDateTime.now(date.getZone());
  ZonedDateTime tempDate = ZonedDateTime.from(date);

  long years = tempDate.until(now, ChronoUnit.YEARS);
  tempDate = tempDate.plusYears(years);

  long months = tempDate.until(now, ChronoUnit.MONTHS);
  tempDate = tempDate.plusMonths(months);

  long days = tempDate.until(now, ChronoUnit.DAYS);
  tempDate = tempDate.plusDays(days);

  long hours = tempDate.until(now, ChronoUnit.HOURS);
  tempDate = tempDate.plusHours(hours);

  long minutes = tempDate.until(now, ChronoUnit.MINUTES);
  tempDate = tempDate.plusMinutes(minutes);

  long seconds = tempDate.until(now, ChronoUnit.SECONDS);

  Age age = getDefault();

  if (years > 0) {
   age.years = years;
  }

  if (months > 0) {
   age.months = months;
  }

  if (days > 0) {
   age.days = days;
  }

  if (hours > 0) {
   age.hours = hours;
  }

  if (minutes > 0) {
   age.minutes = minutes;
  }

  if (seconds > 0) {
   age.seconds = seconds;
  }

  return age;
 }

 /**
  * Sets the given years to this object.
  * 
  * @author TapasB
  * @param years
  *            - years to set
  * @return this instance for chain call
  */
 public Age setYears(long years) {
  checkValidValue("years", 
    ValueRange.of(0, ChronoField.YEAR.range().getMaximum()), 
    years);
  this.years = years;
  return this;
 }

 /**
  * Sets the given months to this object.
  * 
  * @author TapasB
  * @param months
  *            - months to set
  * @return this instance for chain call
  */
 public Age setMonths(long months) {
  checkValidValue("months", 
    ValueRange.of(0, ChronoField.MONTH_OF_YEAR.range().getMaximum()), 
    months);
  this.months = months;
  return this;
 }

 /**
  * Sets the given days to this object.
  * 
  * @author TapasB
  * @param days
  *            - days to set
  * @return this instance for chain call
  */
 public Age setDays(long days) {
  checkValidValue("days", 
    ValueRange.of(0, ChronoField.DAY_OF_MONTH.range().getMaximum()), 
    days);
  this.days = days;
  return this;
 }

 /**
  * Sets the given hours to this object.
  * 
  * @author TapasB
  * @param hours
  *            - hours to set
  * @return this instance for chain call
  */
 public Age setHours(long hours) {
  checkValidValue("hours", 
    ValueRange.of(0, ChronoField.HOUR_OF_DAY.range().getMaximum()), 
    hours);
  this.hours = hours;
  return this;
 }

 /**
  * Sets the given minutes to this object.
  * 
  * @author TapasB
  * @param minutes
  *            - minutes to set
  * @return this instance for chain call
  */
 public Age setMinutes(long minutes) {
  checkValidValue("minutes", 
    ValueRange.of(0, ChronoField.MINUTE_OF_HOUR.range().getMaximum()), 
    minutes);
  this.minutes = minutes;
  return this;
 }

 /**
  * Sets the given seconds to this object.
  * 
  * @author TapasB
  * @param seconds
  *            - seconds to set
  * @return this instance for chain call
  */
 public Age setSeconds(long seconds) {
  checkValidValue("seconds", 
    ValueRange.of(0, ChronoField.SECOND_OF_MINUTE.range().getMaximum()), 
    seconds);
  this.seconds = seconds;
  return this;
 }

 /**
  * Sets the given value to this object to the given field defined by
  * {@link ChronoUnit}.
  * 
  * <p>
  * The accepted list of values are:
  * <ul>
  * <li>ChronoUnit.YEARS</li>
  * <li>ChronoUnit.MONTHS</li>
  * <li>ChronoUnit.DAYS</li>
  * <li>ChronoUnit.HOURS</li>
  * <li>ChronoUnit.MINUTES</li>
  * <li>ChronoUnit.SECONDS</li>
  * </ul>
  * </p>
  * 
  * @author TapasB
  * @param value
  *            - value to set
  * @param unit
  *            - field to which the value needs to be set
  * @return this instance for chain call
  * @throws UnsupportedOperationException
  *             if the unit passed to it is not belongs to the allowed list
  *             of values
  */
 public Age set(long value, ChronoUnit unit) throws UnsupportedOperationException {
  Objects.requireNonNull(unit, "unit");

  switch (unit) {
   case YEARS:
    return setYears(value);

   case MONTHS:
    return setMonths(value);

   case DAYS:
    return setDays(value);

   case HOURS:
    return setHours(value);

   case MINUTES:
    return setMinutes(value);

   case SECONDS:
    return setSeconds(value);

   default:
    throw new UnsupportedOperationException("Unit " + unit + " not supported");
  }
 }

 /**
  * Calculates the <code>Age</code> and returns the birth date as
  * {@link LocalDateTime}.
  * 
  * @author TapasB
  * @return date of birth as <code>LocalDateTime</code>
  */
 public LocalDateTime getDateOfBirth() {
  LocalDateTime now = LocalDateTime.now();
  LocalDateTime dob = now.minus(this.years, ChronoUnit.YEARS).
    minus(this.months, ChronoUnit.MONTHS).
    minus(this.days, ChronoUnit.DAYS).
    minus(this.hours, ChronoUnit.HOURS).
    minus(this.minutes, ChronoUnit.MINUTES).
    minus(this.seconds, ChronoUnit.SECONDS);

  return dob;
 }

 /**
  * Calculates the <code>Age</code> and returns the birth date as
  * {@link ZonedDateTime} with respect to the given {@link ZoneId}.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return date of birth as <code>ZonedDateTime</code>
  */
 public ZonedDateTime getDateOfBirth(ZoneId zone) {
  ZonedDateTime now = ZonedDateTime.now(zone);
  ZonedDateTime dob = now.minus(this.years, ChronoUnit.YEARS).
    minus(this.months, ChronoUnit.MONTHS).
    minus(this.days, ChronoUnit.DAYS).
    minus(this.hours, ChronoUnit.HOURS).
    minus(this.minutes, ChronoUnit.MINUTES).
    minus(this.seconds, ChronoUnit.SECONDS);

  return dob;
 }

 /**
  * Returns elapsed seconds from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return seconds
  */
 public long asSeconds() {
  return asSeconds(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed seconds from date of birth for this <code>Age</code> for
  * the given. zone
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return seconds
  */
 public long asSeconds(ZoneId zone) {
  return calculateDifference(ChronoUnit.SECONDS, zone);
 }

 /**
  * Returns elapsed minutes from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return minutes
  */
 public long asMinutes() {
  return asMinutes(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed minutes from date of birth for this <code>Age</code> for
  * the given zone.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return minutes
  */
 public long asMinutes(ZoneId zone) {
  return calculateDifference(ChronoUnit.MINUTES, zone);
 }

 /**
  * Returns elapsed hours from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return hours
  */
 public long asHours() {
  return asHours(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed hours from date of birth for this <code>Age</code> for
  * the given zone.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return hours
  */
 public long asHours(ZoneId zone) {
  return calculateDifference(ChronoUnit.HOURS, zone);
 }

 /**
  * Returns elapsed days from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return days
  */
 public long asDays() {
  return asDays(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed days from date of birth for this <code>Age</code> for the
  * given zone.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return days
  */
 public long asDays(ZoneId zone) {
  return calculateDifference(ChronoUnit.DAYS, zone);
 }

 /**
  * Returns elapsed weeks from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return weeks
  */
 public long asWeeks() {
  return asWeeks(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed weeks from date of birth for this <code>Age</code> for
  * the given zone.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return weeks
  */
 public long asWeeks(ZoneId zone) {
  return calculateDifference(ChronoUnit.WEEKS, zone);
 }

 /**
  * Returns elapsed months from date of birth for this <code>Age</code>.
  * 
  * @author TapasB
  * @return months
  */
 public long asMonths() {
  return asMonths(ZoneId.systemDefault());
 }

 /**
  * Returns elapsed months from date of birth for this <code>Age</code> for
  * the given zone.
  * 
  * @author TapasB
  * @param zone
  *            - the zone ID to use
  * @return months
  */
 public long asMonths(ZoneId zone) {
  return calculateDifference(ChronoUnit.MONTHS, zone);
 }

 /**
  * Returns string representation of the <code>Age</code> in the following
  * format: <br/>
  * <code>A Years B Months C Days D Hours E Minutes F Seconds</code> <br/>
  * Any field except Seconds will be omitted if the value is 0.
  * 
  * @author TapasB
  * @return the string representation
  */
 public String getDisplayString() {
  StringBuilder builder = new StringBuilder();

  setString(years, builder, "Years");
  setString(months, builder, "Months");
  setString(days, builder, "Days");
  setString(hours, builder, "Hours");
  setString(minutes, builder, "Minutes");

  builder.append(seconds);
  builder.append(" Seconds.");

  return builder.toString();
 }

 /**
  * Returns string representation of the <code>Age</code> in the following
  * format: <br/>
  * <code>A Years B Months C Days D Hours E Minutes F Seconds</code> <br/>
  * Any field except Seconds will be omitted if the value is 0.
  * 
  * @author TapasB
  * @return the string representation
  */
 @Override
 public String toString() {
  return getDisplayString();
 }

 /**
  * Compares two <code>Age</code> objects.
  * 
  * @author TapasB
  * @param age
  *            - the other <code>Age</code> to be compared
  * @return the value 0 if the argument <code>Age</code> is equal to this
  *         <code>Age</code>; a value less than 0 if this <code>Age</code> is
  *         before the <code>Age</code> argument; and a value greater than 0
  *         if this <code>Age</code> is after the <code>Age</code> argument.
  */
 @Override
 public int compareTo(Age age) {
  Objects.requireNonNull(age, "age");
  long thisSeconds = asSeconds();
  long otherSeconds = age.asSeconds();
  return Long.compare(thisSeconds, otherSeconds);
 }

 /**
  * Creates and returns a copy of this object with the same years, months,
  * days, hours, minutes and seconds.
  * 
  * @author TapasB
  * @return a clone of this instance of <code>Age</code>
  */
 @Override
 protected Age clone() {
  return of(years, months, days, hours, minutes, seconds);
 }

 /**
  * Returns a hash code value for the <code>Age</code> object.
  * 
  * @author TapasB
  * @return a hash code value for this object
  */
 @Override
 public int hashCode() {
  final int prime = 31;
  int result = 1;
  Long thisSeconds = asSeconds();
  int intValue = thisSeconds.intValue();
  result = prime * result + (int) (intValue ^ (intValue >>> 32));
  return result;
 }

 /**
  * Indicates whether some other <code>Age</code> object is same to this one.
  * 
  * @author TapasB
  * @param obj
  *            - the reference object with which to compare
  * @return true if this object is the same as the obj argument; false
  *         otherwise.
  * @see java.lang.Object#equals(java.lang.Object)
  */
 @Override
 public boolean equals(Object obj) {
  if (this == obj) {
   return true;
  }

  if (obj == null) {
   return false;
  }

  if (getClass() != obj.getClass()) {
   return false;
  }

  Age age = (Age) obj;
  return compareTo(age) == 0;
 }

 // Checks the validity of the field value
 private void checkValidValue(String field, ValueRange range, long value) {
  if (!range.isValidValue(value)) {
   throw new DateTimeException(getInvalidFieldMessage(field, range, value));
  }
 }

 // Returns message in case of invalid value which is used by
 // DateTimeException
 private String getInvalidFieldMessage(String field, ValueRange range, long value) {
  return "Invalid value " + value + " for " + field + ". Valid values: (" + range.getMinimum() + ", " + range.getMaximum() + ").";
 }

 // Appends the field value of Age to the StringBuilder with the token
 private void setString(long value, StringBuilder builder, String token) {
  if (value > 0) {
   builder.append(value);
   builder.append(" ").append(token).append(" ");
  }
 }

 // Calculates the amount of time with respect to the given ChronoUnit
 // and ZoneId between the birth date and now
 private long calculateDifference(ChronoUnit chronoUnit, ZoneId zone) {
  Objects.requireNonNull(chronoUnit);
  Objects.requireNonNull(zone);
  ZonedDateTime dob = getDateOfBirth(zone);
  ZonedDateTime now = ZonedDateTime.now(zone);
  return chronoUnit.between(dob, now);
 }
}

Few example code to use:

public static void getDateOfBirthTest() {
 Age age = Age.of(29, 8, 28, 12, 49, 0);
 System.out.println(age.getDateOfBirth());
}

public static void getAgeFromDateTest() {
 Age age = Age.fromDateOfBirth(LocalDateTime.of(1984, Month.DECEMBER, 16, 7, 45, 0));
 System.out.println(age);
}

public static void ageAsUnitsTest() {
 Age age = Age.fromDateOfBirth(LocalDateTime.of(1984, Month.DECEMBER, 16, 7, 45, 0));
 System.out.println(age.asWeeks());
}

@SuppressWarnings("resource")
public static void serializationTest() throws FileNotFoundException, IOException, ClassNotFoundException {
 Age age = Age.fromDateOfBirth(LocalDateTime.of(1984, Month.DECEMBER, 16, 7, 45));
 System.out.println(age);
 
 ObjectOutputStream outputStream = new ObjectOutputStream(new FileOutputStream(new File("C:/tmp")));
 outputStream.writeObject(age);
 outputStream.flush();
 
 ObjectInputStream inputStream = new ObjectInputStream(new FileInputStream(new File("C:/tmp")));
 age = Age.class.cast(inputStream.readObject());
 System.out.println(age);
}

public static void equalsTest() {
 Age age = Age.of(29, 8, 28, 12, 49, 0);
 Age clone = age.clone();
 System.out.println(age.equals(clone));
}

While developing this class I was stuck to calculate the difference between to date-time and I got help from one SO user and I really appreciate that.
You comments and suggestion is appreciable to improve it.
Happy coding.

Convert String to Character Array without calling toCharArray method

One post from LinkedIn came into my sight questioning that how to compare two String objects without using any inbuilt methods of this class. The solution iss trivial, comparing the lengths and every characters of the given strings, but to convert the String into char[] one need to call toCharArray() method and which is not permissible for the OP.
So to solve this problem I came up with a solution which I would like to share with you. String class stores the characters internally within a field called value and the signature of this field is:

private final char value[];

My intention is to deal with this field directly and for this type of cases Java Reflection comes very handy. So I wrote the following code which might come helpful for me in future or for you.

@SuppressWarnings({ "rawtypes", "unchecked" })
public static char[] toCharArray(String str) throws SecurityException, NoSuchFieldException, IllegalArgumentException, IllegalAccessException {
 final Field field = String.class.getDeclaredField("value");
 AccessController.doPrivileged(new PrivilegedAction() {

  @Override
  public Object run() {
   field.setAccessible(true);
   return null;
  }
 });
  
 Object obj = field.get(str);
 char[] charArr = char[].class.cast(obj);
 return charArr;
}

Hope it will help.