String Operations and StringBuilder

Code

public class StringDemo {
    public static void main(String[] args) {
        String s = "Hello, World";

        System.out.println(s.length());
        System.out.println(s.substring(0, 5));   // Hello
        System.out.println(s.charAt(7));         // W

        String[] parts = s.split(", ");
        String joined = String.join(" | ", parts);

        boolean has = s.contains("World");
        int idx = s.indexOf("o");

        StringBuilder sb = new StringBuilder();
        for (int i = 0; i < 3; i++) sb.append(i);
        System.out.println(sb); // 012

        String json = """
            {"name": "Alice"}
            """;
        System.out.println(json);
    }
}

Explanation

Covers common String methods (length, substring, charAt, split, join, contains, indexOf) and StringBuilder for efficient concatenation in loops. Strings are immutable in Java, so StringBuilder avoids creating intermediate objects. Java 15+ text blocks (""") simplify multi-line string literals like JSON or SQL.

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