PATTERN

The pattern that an email address should match.

The underlying value is ^\S+@\S+\.\S+$.

Here's the explanation associated to each symbol used in this pattern:

^ Beginning. Matches the beginning of the string, or the beginning of a line if the multiline flag (m) is enabled.
\S Not whitespace. Matches any character that is not a whitespace character (spaces, tabs, line breaks).
+ Quantifier. Match 1 or more of the preceding token.
@ Character. Match a "@" character (char code 64).
\. Escaped character. Matches a "." character (char code 46).
$ End. Matches the end of the string, or the end of a line if the multiline flag (m) is enabled.

Calling from Kotlin

Here's an example of calling this function from Kotlin code:

val pattern: String = EmailAddress.PATTERN
println(pattern) // ^\S+@\S+\.\S+$

Calling from Java

Here's an example of calling this function from Java code:

final String pattern = EmailAddress.PATTERN;
System.out.println(pattern); // ^\S+@\S+\.\S+$