// Optional chaining // Optional<T> is a container that may or may not hold a value, avoiding NullPointerException import java.util.Optional; public class Main { // Method that may return null — represented as Optional static Optional<String> findUserById(int id) { if (id == 1) return Optional.of("Alice"); // value present if (id == 2) return Optional.of("Bob"); return Optional.empty(); // no value } static Optional<String> getEmailForUser(String name) { if (name.equals("Alice")) return Optional.of("alice@example.com"); return Optional.empty(); } public static void main(String[] args) { // ── isPresent / get ── Optional<String> user1 = findUserById(1); if (user1.isPresent()) { System.out.println("Found: " + user1.get()); } // ── orElse: default value if empty ── String user3 = findUserById(99).orElse("Guest"); System.out.println("User 99: " + user3); // ── orElseGet: default from supplier ── String user4 = findUserById(99).orElseGet(() -> "Anonymous_" + 99); System.out.println("User 99 (supplier): " + user4); // ── map: transform value if present ── String upper = findUserById(2) .map(name -> name.toUpperCase()) .orElse("NO USER"); System.out.println("Uppercase: " + upper); // ── flatMap: chain Optionals (Optional chaining) ── // flatMap avoids Optional<Optional<String>> String email = findUserById(1) .flatMap(name -> getEmailForUser(name)) .orElse("no-email@example.com"); System.out.println("Email for user 1: " + email); // User with no email String email2 = findUserById(2) .flatMap(name -> getEmailForUser(name)) .orElse("no-email@example.com"); System.out.println("Email for user 2: " + email2); // ── ifPresent: run action only if value exists ── findUserById(1).ifPresent(name -> System.out.println("Hello, " + name + "!")); } }

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