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// String literals (stored in the String Pool)
String greeting = "Hello, World!";
String empty = "";

// Using new keyword (creates a separate object on the heap)
String s = new String("Hello");

// String Pool: identical literals share the same object
String a = "Java";
String b = "Java";
System.out.println(a == b);      // true (same pool reference)
System.out.println(a.equals(b)); // true (same content)

// Text Blocks (Java 13+) for multi-line strings
String json = """
        {
            "name": "Alice",
            "age": 25
        }
        """;
System.out.println(json);

String text = "  Hello, Java World!  ";

// Length and checking
System.out.println(text.length());         // 22
System.out.println(text.isEmpty());        // false
System.out.println(text.isBlank());        // false (Java 11+)

// Case conversion
System.out.println(text.toUpperCase());    // "  HELLO, JAVA WORLD!  "
System.out.println(text.toLowerCase());    // "  hello, java world!  "
System.out.println(text.trim());           // "Hello, Java World!" (removes whitespace)
System.out.println(text.strip());          // Same as trim but handles Unicode (Java 11+)

// Searching
System.out.println(text.contains("Java"));       // true
System.out.println(text.indexOf("Java"));        // 9
System.out.println(text.startsWith("  Hello"));  // true
System.out.println(text.endsWith("!  "));        // true

// Extracting
System.out.println(text.substring(9, 13));       // "Java"
System.out.println(text.charAt(2));              // 'H'

// Replacing
System.out.println(text.replace("Java", "PHP")); // "  Hello, PHP World!  "
System.out.println(text.replaceAll("\\s+", " "));// Regex: collapse whitespace

// Splitting
String csv = "red,green,blue,yellow";
String[] colors = csv.split(",");
// ["red", "green", "blue", "yellow"]

// Joining (Java 8+)
String joined = String.join(" | ", colors);
// "red | green | blue | yellow"

String s1 = "Hello";
String s2 = "hello";
String s3 = new String("Hello");

// Content comparison (ALWAYS use these for strings)
System.out.println(s1.equals(s3));            // true
System.out.println(s1.equalsIgnoreCase(s2));  // true

// Reference comparison (DO NOT use for content)
System.out.println(s1 == s3);                 // false (different objects)

// Lexicographic comparison (for sorting)
System.out.println("apple".compareTo("banana")); // negative (apple comes first)
System.out.println("banana".compareTo("apple")); // positive

// Null-safe comparison
String maybeNull = null;
System.out.println("Hello".equals(maybeNull));   // false (safe)
// System.out.println(maybeNull.equals("Hello")); // NullPointerException!

// Problem: String concatenation in loops creates many temporary objects
String result = "";
for (int i = 0; i < 1000; i++) {
    result += i + ",";  // Creates 1000 new String objects! Slow.
}

// Solution: StringBuilder modifies the same buffer
StringBuilder sb = new StringBuilder();
for (int i = 0; i < 1000; i++) {
    sb.append(i).append(",");
}
String fast = sb.toString();

// Common StringBuilder methods
StringBuilder builder = new StringBuilder("Hello");
builder.append(" World");       // "Hello World"
builder.insert(5, ",");         // "Hello, World"
builder.replace(0, 5, "Hi");    // "Hi, World"
builder.reverse();              // "dlroW ,iH"
builder.delete(0, 5);           // " ,iH"

System.out.println(builder.toString());

String name = "Alice";
int age = 25;
double score = 95.5;

// String.format() — like printf
String msg = String.format("Name: %s, Age: %d, Score: %.1f%%", name, age, score);
System.out.println(msg);  // Name: Alice, Age: 25, Score: 95.5%

// Formatted string (Java 15+)
String modern = "Name: %s, Age: %d".formatted(name, age);

// Common format specifiers:
// %s = string, %d = integer, %f = float, %.2f = 2 decimal places
// %n = newline, %% = literal percent sign