Working with Strings

public class StringCreation {
    public static void main(String[] args) {
        // String literal (recommended)
        String url = "https://demo-bank.example.com";

        // String object (avoid — creates unnecessary object)
        String url2 = new String("https://demo-bank.example.com");

        // Empty and blank
        String empty = "";
        String blank = "   ";

        System.out.println(url.equals(url2));  // true — same content
        System.out.println(url == url2);       // false — different objects
    }
}

public class StringMethods {
    public static void main(String[] args) {
        String title = "  Welcome to Demo Bank  ";

        // Length and trim
        System.out.println(title.length());          // 24 (includes spaces)
        System.out.println(title.trim());            // "Welcome to Demo Bank"
        System.out.println(title.trim().length());   // 20

        // Case conversion
        String status = "Pass";
        System.out.println(status.toUpperCase());    // "PASS"
        System.out.println(status.toLowerCase());    // "pass"

        // Checking content
        String msg = "Login successful";
        System.out.println(msg.contains("successful"));  // true
        System.out.println(msg.startsWith("Login"));     // true
        System.out.println(msg.endsWith("failed"));      // false
        System.out.println(msg.isEmpty());               // false

        // Finding and extracting
        String email = "admin@testerrank.com";
        System.out.println(email.indexOf("@"));          // 5
        System.out.println(email.substring(6));          // "testerrank.com"
        System.out.println(email.substring(0, 5));       // "admin"
    }
}

public class ReplaceAndSplit {
    public static void main(String[] args) {
        // Replace
        String price = "$1,299.99";
        String clean = price.replace("$", "").replace(",", "");
        double amount = Double.parseDouble(clean);
        System.out.println(amount);  // 1299.99

        // Split
        String csv = "Chrome,Firefox,Safari,Edge";
        String[] browsers = csv.split(",");
        for (String b : browsers) {
            System.out.println("Browser: " + b);
        }

        // Split with limit
        String log = "ERROR: Login failed: invalid password";
        String[] parts = log.split(": ", 2);
        System.out.println("Level: " + parts[0]);    // ERROR
        System.out.println("Message: " + parts[1]);  // Login failed: invalid password
    }
}

public class StringCompare {
    public static void main(String[] args) {
        String expected = "Dashboard";
        String actual = "dashboard";

        // WRONG — compares references
        System.out.println(expected == actual);               // may be false

        // CORRECT — compares content
        System.out.println(expected.equals(actual));          // false (case-sensitive)
        System.out.println(expected.equalsIgnoreCase(actual)); // true

        // Null-safe comparison (put the known string first)
        String pageTitle = null;
        // pageTitle.equals("Dashboard");  // NullPointerException!
        System.out.println("Dashboard".equals(pageTitle));    // false — no exception
    }
}

public class Immutability {
    public static void main(String[] args) {
        String name = "hello";
        name.toUpperCase();          // returns "HELLO" but name is still "hello"
        System.out.println(name);    // "hello"

        name = name.toUpperCase();   // reassign to capture the result
        System.out.println(name);    // "HELLO"
    }
}

public class StringBuilderDemo {
    public static void main(String[] args) {
        StringBuilder report = new StringBuilder();
        report.append("Test Report\n");
        report.append("===========\n");

        String[] tests = {"Login", "Search", "Checkout"};
        String[] results = {"PASS", "PASS", "FAIL"};

        for (int i = 0; i < tests.length; i++) {
            report.append(tests[i]).append(": ").append(results[i]).append("\n");
        }

        System.out.println(report.toString());
    }
}

Test Report
===========
Login: PASS
Search: PASS
Checkout: FAIL