Escape Sequences

// ── All Java escape sequences: ───────────────────────────────────────
//
//  Sequence   Name                 Unicode   Decimal
//  ─────────  ───────────────────  ────────  ───────
//  	         Horizontal tab       	    9
//  
         Newline (line feed)  
    10
//  
         Carriage return      
    13
//           Form feed                12
//           Backspace                8
//  '         Single quote         '    39
//  "         Double quote         "    34
//  \         Backslash            \    92
//  \0–\377    Octal escape         varies    0–255


// ── Demonstrating each escape sequence: ──────────────────────────────
System.out.println("Tab:	here");           // Tab:    here
System.out.println("Line
Break");          // Line
                                            // Break
System.out.println("Backspace");          // Bacspace  (deletes 'k' visually)
System.out.println("Formfeed");           // Form (page break — rarely visible)
System.out.println("Carriage
Return");     // Return (cursor to line start)
System.out.println("Single 'quote'");     // Single 'quote'
System.out.println("Double "quote"");     // Double "quote"
System.out.println("Back\slash");          // Backslash

// ── Char literals also use escape sequences: ──────────────────────────
char tab        = '	';
char newline    = '
';
char singleQuote = ''';
char backslash  = '\';

System.out.println("Tab char value: " + (int) tab);       // 9
System.out.println("Newline value:  " + (int) newline);   // 10

// ── Unrecognised escape — compile error: ──────────────────────────────
// String s = "hello p world";   // ERROR: illegal escape character
// String s = "C:path	oile";  // ERROR: p and 	 interpreted

// ── Correct file paths on Windows: ────────────────────────────────────
String path1 = "C:\Users\Alice\Documents\file.txt";  // doubled backslash
String path2 = "C:/Users/Alice/Documents/file.txt";      // forward slash also works
System.out.println(path1);   // C:UsersAliceDocumentsile.txt

// ── 
 — newline inside a string: ───────────────────────────────────
String address = "123 Main Street
" +
                 "Springfield
" +
                 "IL 62701";
System.out.println(address);
// Output:
// 123 Main Street
// Springfield
// IL 62701

// ── Multiple 
 — create blank lines: ────────────────────────────────
System.out.println("Section 1

Section 2");
// Output:
// Section 1
//              ← blank line
// Section 2

// ── 	 — tab alignment: ───────────────────────────────────────────────
System.out.println("Name		Score	Grade");
System.out.println("Alice		95	A");
System.out.println("Bob		87	B");
System.out.println("Charlie		72	C");
// Output (approximate — tab stops vary by environment):
// Name            Score   Grade
// Alice           95      A
// Bob             87      B
// Charlie         72      C
// NOTE: use printf() for reliable column alignment — tabs are not
// consistent across terminals.

// ── 
 vs %n vs System.lineSeparator(): ──────────────────────────────
System.out.printf("Line 1
Line 2%n");
// 
  → always Unix LF  (char 10)       — fine for most uses
// %n  → System.lineSeparator()          — platform-specific (CRLF on Windows)
// Use %n in printf for files written on Windows.
// Use 
 for console output (fine on all platforms).

String ls = System.lineSeparator(); // "
" on Linux/Mac, "
" on Windows
System.out.println("Cross-platform" + ls + "newline");

// ── Double quote inside a String: ────────────────────────────────────
String quote   = "She said "Hello!"";
String jsonStr = "{"name": "Alice", "age": 30}";
String html    = "<a href="https://example.com">Link</a>";

System.out.println(quote);    // She said "Hello!"
System.out.println(jsonStr);  // {"name": "Alice", "age": 30}
System.out.println(html);     // <a href="https://example.com">Link</a>

// ── Single quote in char literal: ────────────────────────────────────
char apostrophe = ''';
System.out.println("Char: " + apostrophe);   // Char: '

// Single quote does NOT need escaping inside a String:
String possessive = "Alice's book";          // fine — no escape needed
System.out.println(possessive);              // Alice's book

// ── Backslash — must be doubled everywhere: ───────────────────────────
String winPath  = "C:\Program Files\Java\bin";
String regexSep = "\s+";          // regex for one or more whitespace chars
String regexDig = "\d{3}-\d{4}"; // regex for phone number pattern

System.out.println(winPath);    // C:Program FilesJavain
System.out.println(regexSep);   // s+
System.out.println(regexDig);   // d{3}-d{4}

// ── Backslash in regex — four backslashes for literal : ───────────────
// To match a literal backslash with regex:
// - String needs "\\" (4 chars → 2 actual backslashes)
// - Regex engine sees "\" (1 escaped backslash = match literal )
String text    = "C:\Users\Alice";
String escaped = text.replaceAll("\\", "/");
System.out.println(escaped);    // C:/Users/Alice

// ── Java 15+ Text Blocks — avoid most escaping: ──────────────────────
String json = """
        {
            "name": "Alice",
            "age": 30,
            "city": "London"
        }
        """;
System.out.println(json);
// No escaped quotes needed — text block handles it.

// ── Unicode escape syntax: \uXXXX (four hex digits): ─────────────────
char   omega   = 'Ω';    // Ω — Greek capital omega
char   heart   = '♥';    // ♥ — black heart suit
char   euro    = '€';    // € — euro sign
char   snowman = '☃';    // ☃ — snowman

System.out.println("Omega: "   + omega);    // Omega: Ω
System.out.println("Heart: "   + heart);    // Heart: ♥
System.out.println("Euro: "    + euro);     // Euro: €
System.out.println("Snowman: " + snowman);  // Snowman: ☃

// ── Unicode in strings: ───────────────────────────────────────────────
String greeting  = "你好";          // 你好 — Mandarin "Hello"
String copyright = "Copyright © 2025"; // Copyright © 2025
String trademark = "Java™";            // Java™

System.out.println(greeting);              // 你好
System.out.println(copyright);            // Copyright © 2025
System.out.println(trademark);            // Java™

// ── Unicode processed at lexical phase — can appear in identifiers: ───
int café = 42;    // valid! é = é — identifier is "café"
System.out.println(café);   // 42

// ── Surprising behaviour — Unicode in comments: ───────────────────────
// 
 is a newline — this comment "ends" at 
 even in comments
// The following would cause a compile error if 
 appeared mid-comment:
// int x = 1; // set x
x = 2; ← 
 is a real newline here

// ── Unicode for supplementary characters (code points > U+FFFF): ──────
// Characters above U+FFFF require surrogate pairs or String.codePointAt:
String emoji = "😀";    // 😀 — grinning face (U+1F600)
System.out.println(emoji);        // 😀
System.out.println("Length: " + emoji.length());      // 2 (two chars)
System.out.println("Code points: " +
    emoji.codePointCount(0, emoji.length()));          // 1 (one symbol)

// ── Octal escapes (legacy — avoid in new code): ───────────────────────
char octalA   = '\101';   // 'A' (octal 101 = decimal 65)
char octalZ   = '\132';   // 'Z' (octal 132 = decimal 90)
char maxOctal = '\377';   // highest octal escape = 255 decimal
System.out.println("Octal A: " + octalA);   // A
// Prefer \uXXXX over octal — clearer and more portable.

// ── Text block syntax: ──────────────────────────────────────────────
//  String name = """
//          content here
//          more content
//          """;
//
//  Opening """ must be followed by a newline.
//  Closing """ position determines indentation stripping.

// ── No escaping needed for double quotes: ─────────────────────────────
String json = """
        {
            "service": "order-service",
            "version": "2.1.0",
            "active": true
        }
        """;
System.out.println(json);
// Output:
// {
//     "service": "order-service",
//     "version": "2.1.0",
//     "active": true
// }

// ── HTML without escaped quotes: ─────────────────────────────────────
String html = """
        <html>
            <body>
                <h1>Hello, "World"!</h1>
                <p class="intro">Welcome.</p>
            </body>
        </html>
        """;

// ── SQL queries — much cleaner than concatenation: ────────────────────
String sql = """
        SELECT u.id, u.name, o.total
        FROM   users u
        JOIN   orders o ON o.user_id = u.id
        WHERE  u.active = true
          AND  o.total > 100.00
        ORDER  BY o.total DESC
        """;

// ── New escape sequences in text blocks: ─────────────────────────────

// s — explicit space (prevents trailing whitespace stripping):
String columns = """
        Alice   s
        Bob     s
        Charlie s
        """;
// The s ensures the trailing spaces are preserved.

//   (backslash + newline) — line continuation (suppress newline): ────
String longLine = """
        This is a very long string that         continues on the next source line         but has no newlines in the output.
        """;
System.out.println(longLine);
// Output: This is a very long string that continues on the next source
//         line but has no newlines in the output.

// ── Standard escape sequences still work in text blocks: ─────────────
String mixed = """
        Line 1	Tabbed
        Line 2	Tabbed
        """;
System.out.print(mixed);
// Output:
// Line 1  Tabbed
// Line 2  Tabbed