Unravel › Java concepts › Strings and text

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At a glance

1. 1Character.isDigit(c), isLetter, isWhitespace, toUpperCase(c) classify and convert one charc - '0' turns the digit character '7' into the number 7.
2. 2s.getBytes(StandardCharsets.UTF_8) and new String(bytes, StandardCharsets.UTF_8) convert between text and bytesThe no-argument versions use the platform default, which differs between machines.
3. 3Characters outside the basic plane (many emoji) take two chars (a surrogate pair), so length() and charAt count UTF-16 unitscodePoints() and codePointCount count real characters.

• Typical bugs: "mojibake" (UTF-8 bytes read as Latin-1), a file written on Windows and read on Linux, and reverse() that splits an emoji in half
• Visually identical text can be different code points (é as one char or e plus an accent)
• Since Java 18 the default charset is UTF-8, but older versions use the OS setting (-Dfile.encoding)

import java.nio.charset.StandardCharsets;public class Digits {  static int sumDigits(String s) {    int total = 0;    for (char c : s.toCharArray()) if (Character.isDigit(c)) total += c - '0';    return total;  }  static byte[] pack(String s) { return s.getBytes(StandardCharsets.UTF_8); }}

1. line 5 uses Character, the core of Characters, Unicode and encodings
2. line 8 uses getBytes, the core of Characters, Unicode and encodings

How Unravel recognises it

When you paste code, Unravel looks for these signs of characters, unicode and encodings. Spotting them yourself is a good habit when you read unfamiliar code:

• Types: Character Normalizer
• Method calls: codePointAt() codePoints() getBytes() isLetter() isDigit() isLetterOrDigit() isWhitespace() isUpperCase() getNumericValue()

Part of a learning path

• Text, numbers and arrays · previous: Formatting text and numbers · next: Primitive types and floating point

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