Editing Comparison of C Sharp and Java (section)

==== Built-in compound data types ====
Both languages treat [[String (computer science)|strings]] as ([[immutable object|immutable]]) objects of reference type. In both languages, the type contains several methods to manipulate strings, parse, format, etc. In both languages [[regular expression]]s are considered an external feature and are implemented in separate classes.

Both languages' libraries define classes for working with dates, times, [[time zone]]s, and [[calendar]]s in different cultures. Java provides {{code|java.util.Date}}, a mutable reference type with millisecond precision, and (since Java 8) the {{code|java.time}} package (including classes such as {{mono|LocalDate}}, {{mono|LocalTime}}, and {{mono|LocalDateTime}} for date-only, time-only, and date-and-time values), a set of immutable reference types with [[nanosecond]] precision.<ref>{{cite web |url=https://docs.oracle.com/javase/8/docs/api/java/time/package-summary.html |title=Package java.time (Java Platform SE 8) |publisher=docs.oracle.com |access-date=20 April 2023}}</ref> In contrast, the C# {{code|System.DateTime}} is an immutable struct value type for date-and-time information with 100-nanosecond precision; the .NET 6 API also added {{code|System.DateOnly}} and {{code|System.TimeOnly}}, similar structures for date-only or time-only operations.<ref>{{cite web |url=https://learn.microsoft.com/en-us/dotnet/standard/datetime/how-to-use-dateonly-timeonly |title=How to use the DateOnly and TimeOnly structures |date=12 January 2023 |publisher=learn.microsoft.com |access-date=20 April 2023}}</ref> C# additionally defines a {{code|System.TimeSpan}} type for working with time periods; Java 8 provides the {{code|java.time.Duration}} class for the same purpose. Both languages support date and time arithmetic according to different cultures and time zones.