CharAt

CharAt is a method name used to retrieve a character at a given position within a string. The exact behavior and return type vary by language, with Java and JavaScript providing the most common implementations.

In Java, charAt is a method of java.lang.String. It returns the character at the specified index as a char primitive. Indices start at 0. If index is negative or not less than length(), String.charAt throws IndexOutOfBoundsException. Because Java char is a 16-bit Unicode code unit, characters outside the Basic Multilingual Plane may require additional handling (such as codePointAt) to work with full Unicode code points.

In JavaScript, charAt(index) is a method on String objects that returns a string containing the character at the given position. If the index is out of range or cannot be converted to a valid integer, it returns the empty string. JavaScript strings are sequences of UTF-16 code units, so charAt returns a single code unit, which may be part of a surrogate pair; for full characters you can use codePointAt or iterate with for...of. A related method is charCodeAt(index), which returns the numeric code unit or NaN if the index is out of range. In addition to charAt, the bracket notation s[i] can access a character, but it yields undefined for out-of-range indexes.

Common use cases include extracting specific characters from a string, validating input by position, or iterating over characters in a string. The choice between language-specific methods and alternatives depends on the programming language and the desired handling of Unicode.