Pre-Defined Enum

Overview of built-in Enum provided in Java.

About

A Predefined Enum refers to an enum that is commonly used or provided by a library or framework (such as Java's own standard enums). These enums provide frequently-used constants, such as TimeUnit or DayOfWeek in Java, that offer built-in methods and functionality based on the type.

Examples of Predefined Enums in Java

java.time.temporal.ChronoUnit

It is an enum in the java.time.temporal package in Java, introduced in Java 8 as part of the java.time package for date and time manipulation. It represents units of time, such as days, hours, minutes, seconds, etc., and provides a way to perform date and time arithmetic. ChronoUnit constants can be used along with methods like plus and minus to add or subtract a specified amount of time from a date-time object.

Here are some commonly used ChronoUnit constants:

• NANOS: Nanoseconds

• MICROS: Microseconds

• MILLIS: Milliseconds

• SECONDS: Seconds

• MINUTES: Minutes

• HOURS: Hours

• DAYS: Days

• WEEKS: Weeks

• MONTHS: Months

• YEARS: Years

• DECADES: Decades

• CENTURIES: Centuries

• MILLENNIA: Millennia

• ERAS: Eras

ZonedDateTime currentDateTime = ZonedDateTime.now();
ZonedDateTime futureDateTime = currentDateTime.plus(3, ChronoUnit.HOURS);
ZonedDateTime pastDateTime = currentDateTime.minus(1, ChronoUnit.DAYS);

java.util.concurrent.TimeUnit

Used for specifying time durations in multithreaded code.

Constants include NANOSECONDS, MICROSECONDS, MILLISECONDS, SECONDS, MINUTES, HOURS, and DAYS.

long duration = TimeUnit.SECONDS.toMillis(10); // Converts 10 seconds to milliseconds

java.time.DayOfWeek

Part of the java.time package, this enum represents days of the week.

Constants include MONDAY, TUESDAY, WEDNESDAY, etc.

Built-in methods like .plus(int days) make it easy to calculate future or past days.

DayOfWeek today = DayOfWeek.MONDAY;
DayOfWeek tomorrow = today.plus(1); // Returns TUESDAY

java.nio.file.StandardOpenOption

Provides options for file operations, such as READ, WRITE, APPEND, and CREATE.

These options are used in file I/O to specify how the file should be handled.

Files.write(path, data, StandardOpenOption.APPEND);