tl;dr

Generate text representing the date.

LocalDate                                    // Represent a date-only value, without time-of-day and without time zone, using `java.time.LocalDate` class.
.of( 1982 , 1 , 24 )                         // Specify a date. Notice the sane numbering of both year and month, unlike the legacy classes `Date`/`Calendar`. Returns a `LocalDate` object.
.format(                                     // Generate text to represent the value of the `LocalDate` object.
    DateTimeFormatter
    .ofLocalizedDate( FormatStyle.MEDIUM )   // How long or abbreviated do you want the text.
    .withLocale( Locale.UK )                 // Specify a `Locale` to determine the human language and cultural norms to use in localizing.
)                                            // Returns a `String` object.

24 Jan 1982

Calculate age.

Period
.between(
    LocalDate.of( 1982 , 1 , 24 ) ,
    LocalDate.now( ZoneId.systemDefault() ) 
)
.getYears()

Birthday toast.

MonthDay
.now( 
    ZoneId.systemDefault()   // Specify time zone. For any given moment, the date varies around the globe by time zone.
)
.equals(
    MonthDay.of( 1 , 24 )
)

java.time

The modern approach uses the java.time classes.

From your DatePicker, pull the year, month, and day, passing all three to the factory method for LocalDate.

DatePicker dp = … ;
…
LocalDate localDate = LocalDate.of( dp.getYear() , dp.getMonth() , dp.getDayOfMonth() ) ;

You can define your own formatting pattern when generating text for presentation to the user. But generally better to let java.time automatically localize.

LocalDate localDate = LocalDate.of( 1982 , 1 , 24 ) ;
Locale locale = Locale.UK ; 
DateTimeFormatter f = DateTimeFormatter.ofLocalizedDate( FormatStyle.MEDIUM ).withLocale( locale ) ;
String output = localDate.format( f ) ;

See this code run live at IdeOne.com.

24 Jan 1982

To calculate age, look for the LocalDate related answers on the question: How do I calculate someone’s age in Java?.

To see if today is their birthday, use MonthDay class.

MonthDay birthday = MonthDay.from( localDate ) ;
ZoneId z = ZoneId.of( "America/Montreal" ) ;  // The time zone through which we want to see today's date.
MonthDay monthDay = MonthDay.now( z ) ;
if( monthDay.equals( birthday ) ) {  … Happy Birthday … }

About java.time

The java.time framework is built into Java 8 and later. These classes supplant the troublesome old legacy date-time classes such as java.util.Date, Calendar, & SimpleDateFormat.

To learn more, see the Oracle Tutorial. And search Stack Overflow for many examples and explanations. Specification is JSR 310.

The Joda-Time project, now in maintenance mode, advises migration to the java.time classes.

You may exchange java.time objects directly with your database. Use a JDBC driver compliant with JDBC 4.2 or later. No need for strings, no need for java.sql.* classes. Hibernate 5 & JPA 2.2 support java.time.

Where to obtain the java.time classes?

• Java SE 8, Java SE 9, Java SE 10, Java SE 11, and later – Part of the standard Java API with a bundled implementation.
  • Java 9 adds some minor features and fixes.
• Java SE 6 and Java SE 7
  • Most of the java.time functionality is back-ported to Java 6 & 7 in ThreeTen-Backport.
• Android
  • Later versions of Android bundle implementations of the java.time classes.
  • For earlier Android (<26), the ThreeTenABP project adapts ThreeTen-Backport (mentioned above). See How to use ThreeTenABP….

Use the Date class. Never deal with dates yourself. Its complicated.

https://docs.oracle.com/javase/7/docs/api/java/util/Date.html

and here is a simple tutorial

https://www.javatpoint.com/java-string-to-date

So then you could check if day and month are the same for todays date and then its your birthday

EDIT: As per comments earlier, seems like Date class is no longer cool. Please take a look at the Calendar class

Java: Why is the Date constructor deprecated, and what do I use instead?

Or even better as Basil mentioned check ouy java.time classes. Although i have never used them before.

I am learning android development, and I want to show a notification for users who have birthday today based on their current location. I have a basic DatePicker that gets the date of birth from users using these codes:

String[] MONTHS = {"Jan", "Feb", "Mar", "Apr", "May", "Jun", "Jul", "Aug", "Sep", "Oct", "Nov", "Dec"};
int monthValue = datePicker.getMonth();
String month = MONTHS[monthValue];
String dateofBirth = datePicker.getDayOfMonth() + " " + month + " " + datePicker.getYear();

the user date of birth that I got is in this string format:

24 Jan 1982

Is there a way to calculate user’s birthday age using the date string format above and show a birthday notification on that day every year? For example:

"Today is your 37th birthday!"

I think this feature would be lovely but I don’t know how to calculate it and compare it with today’s date based on different location 🙁

Your help would be very much appreciated. Thank you in advance.