The following example show you how to get the length of a month represented by a java.time.LocalDate and a java.time.YearMonth objects. Both of these classes have a method called lengthOfMonth() that returns the length of month in days represented by those date objects.

package org.kodejava.datetime;

import java.time.LocalDate;
import java.time.Month;
import java.time.YearMonth;

public class LengthOfMonth {
    public static void main(String[] args) {
        // Get the length of month of the current date.
        LocalDate date = LocalDate.now();
        System.out.printf("%s: %d%n%n", date, date.lengthOfMonth());

        // Get the length of month of a year-month combination value
        // represented by the YearMonth object.
        YearMonth yearMonth = YearMonth.of(2020, Month.FEBRUARY);
        System.out.printf("%s: %d%n%n", yearMonth, yearMonth.lengthOfMonth());

        // Repeat a process the get the length of a month for one-year
        // period.
        for (int month = 1; month <= 12; month++) {
            yearMonth = YearMonth.of(2021, Month.of(month));
            System.out.printf("%s: %d%n", yearMonth, yearMonth.lengthOfMonth());
        }
    }
}

The main() method above start by showing you how to get the month length of a LocalDate object. First we create a LocalDate object using the LocalDate.now() static factory method which return today’s date. And then we print out the length of month of today’s date on the following line.

The next snippet use the YearMonth class. We begin by creating a YearMonth object that represent the month of February 2020. We created it using the YearMonth.of() static factory method. We then print out the length of month for those year-month combination.

In the last lines of the example we create a for loop to get all month’s length for the year of 2021 from January to December.

And here are the result of our code snippet above:

2021-11-16: 30

2020-02: 29

2021-01: 31
2021-02: 28
2021-03: 31
2021-04: 30
2021-05: 31
2021-06: 30
2021-07: 31
2021-08: 31
2021-09: 30
2021-10: 31
2021-11: 30
2021-12: 31

In this code snippet you will learn how to parse a string into an instance of LocalDate, LocalTime and LocalDateTime. All of these classes provide a parse() method that accept an argument of string that represent a valid date and time information and convert it into the corresponding object.

If the string passed into the parse() method is not representing a valid date or time information this method throws a RuntimeException of type DateTimeParseException exception. If you want to handle this exception then you should wrap your code inside a try-catch block.

Let’s see the code snippet below as an example:

package org.kodejava.datetime;

import java.time.LocalDate;
import java.time.LocalDateTime;
import java.time.LocalTime;
import java.time.format.DateTimeParseException;

public class DateTimeParseDemo {
    public static void main(String[] args) {

        // Parse string "2021-09-12" into LocalDate instance.
        LocalDate date = LocalDate.parse("2021-09-12");

        // Parse string "17:51:15: into LocalTime instance.
        LocalTime time = LocalTime.parse("17:51:15");

        // Parse string "2021-09-12T17:51:15" into LocalDateTime instance.
        LocalDateTime dateTime = LocalDateTime.parse("2021-09-12T17:51:15");

        System.out.println("date     = " + date);
        System.out.println("time     = " + time);
        System.out.println("dateTime = " + dateTime);

        try {
            // When the string cannot be parsed, a RuntimeException of type
            // DateTimeParseException will be thrown.
            LocalDate date1 = LocalDate.parse("2021-02-31");
            System.out.println("date1     = " + date1);
        } catch (DateTimeParseException e) {
            e.printStackTrace();
        }
    }
}

Running this code snippet will produce the following result:

date     = 2021-09-12
time     = 17:51:15
dateTime = 2021-09-12T17:51:15
java.time.format.DateTimeParseException: Text '2021-02-31' could not be parsed: Invalid date 'FEBRUARY 31'
    at java.base/java.time.format.DateTimeFormatter.createError(DateTimeFormatter.java:2023)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1958)
    at java.base/java.time.LocalDate.parse(LocalDate.java:430)
    at java.base/java.time.LocalDate.parse(LocalDate.java:415)
    at org.kodejava.datetime.DateTimeParseDemo.main(DateTimeParseDemo.java:27)
Caused by: java.time.DateTimeException: Invalid date 'FEBRUARY 31'
    at java.base/java.time.LocalDate.create(LocalDate.java:461)
    at java.base/java.time.LocalDate.of(LocalDate.java:273)
    at java.base/java.time.chrono.IsoChronology.resolveYMD(IsoChronology.java:654)
    at java.base/java.time.chrono.IsoChronology.resolveYMD(IsoChronology.java:126)
    at java.base/java.time.chrono.AbstractChronology.resolveDate(AbstractChronology.java:442)
    at java.base/java.time.chrono.IsoChronology.resolveDate(IsoChronology.java:586)
    at java.base/java.time.chrono.IsoChronology.resolveDate(IsoChronology.java:126)
    at java.base/java.time.format.Parsed.resolveDateFields(Parsed.java:365)
    at java.base/java.time.format.Parsed.resolveFields(Parsed.java:272)
    at java.base/java.time.format.Parsed.resolve(Parsed.java:259)
    at java.base/java.time.format.DateTimeParseContext.toResolved(DateTimeParseContext.java:331)
    at java.base/java.time.format.DateTimeFormatter.parseResolved0(DateTimeFormatter.java:2058)
    at java.base/java.time.format.DateTimeFormatter.parse(DateTimeFormatter.java:1954)
    ... 3 more

As we can see from the output above, parsing a text string of "2021-02-31" give us a DateTimeParseException because the 31st of February is not a valid date.