64. Converting between Date and YearMonth Converting a java.util.Date to JDK 8 java.time.YearMonth can be done based on YearMonth.from(TemporalAccessor temporal). A TemporalAccessor is an interface (more precisely, a framework-level interface) that exposes read-only access to any temporal object including date, time, and offset (a combination of these is also allowed). So, if we convert the […]
Checking leap year – Working with Date and Time
67. Checking leap year This problem become easy as long as we know what is a leap year. In a nutshell, a leap year is any year divisible by 4 (so, year % 4 == 0) that it is not a century (for instance, 100, 200, …, n00). However, if the year represents a century […]
Getting the first and last day of a quarter – Working with Date and Time
69. Getting the first and last day of a quarter Let’s assume that we represent the first and last day of a quarter via this simple class: public final class Quarter { private final Date firstDay; private final Date lastDay; …} Next, we have a java.util.Date and we want the first and the last day […]
Computing pregnancy due date – Working with Date and Time
71. Computing pregnancy due date I’m not an expert in the field but let’s start with these two constants: public static final int PREGNANCY_WEEKS = 40;public static final int PREGNANCY_DAYS = PREGNANCY_WEEKS * 7; Let’s consider the first day as a LocalDate and we want to write a calculator that prints the pregnancy due date, […]
Extracting the count of milliseconds since midnight – Working with Date and Time
73. Extracting the count of milliseconds since midnight So, we have a date-time (let’s say a LocalDateTime or LocalTime) and we want to know how many milliseconds have been passed from midnight to this date-time. Let’s consider that the given date-time is right now: LocalDateTime now = LocalDateTime.now(); Midnight is relative to now, is in […]
Displaying the names of the days of the week – Working with Date and Time
76. Displaying the names of the days of the week One of the hidden gems in Java is java.text.DateFormatSymbols. This class is a wrapper for date-time formatting data such as the names of the days of the week, and the names of the months. All these names are localizable.Typically you will use DateFormatSymbols via a […]
Calculating the middle of the month – Working with Date and Time
79. Calculating the middle of the month Let’s imagine that we have a LocalDate and we want to calculate from it another LocalDate representing the middle of the month. This can be achieved in seconds if we know that the LocalDate API has a method named lengthOfMonth() which returns an integer representing the length of […]
Declaring a Java record – Record and record pattern
83. Declaring a Java record Before diving into Java records let’s think a little bit about how we commonly carry around data into a Java application. You’re right … we define simple classes containing the needed instance fields populated with our data via the constructors of these classes. We also expose some specific getters, and […]