Java 8 Optional Class Quiz | 25 Tricky MCQs for Interviews & Exams

STUDYECRAT Java : Optional Class

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Java Optional Class

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Q1/4

What is the output?

System.out.println("Hello World");

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★ Java 8 Optional: Key Interview Points

1. Safely Handle Null Values

Optional<String> name = Optional.ofNullable(getNameFromDB());
System.out.println(name.orElse("Default"));
// Uses ofNullable() to avoid NPE if getNameFromDB() returns null

• Tip: Always use ofNullable() for uncertain data sources (APIs/DB).
• Real Use: Wrapping JPA repository results to prevent null checks in service layers.

2. Chain Transformations Cleanly

Optional<String> opt = Optional.of(" java ");
String result = opt.map(String::trim)
.map(String::toUpperCase)
.orElse("DEFAULT");
// Chained transformations without null checks

• Tip: Prefer map() over nested if-else for readability.
• Real Use: Processing API responses (e.g., trimming/formatting strings).

3. Fail Fast with orElseThrow()

Optional<User> user = findUserById(123);
User validated = user.orElseThrow(() ->
new UserNotFoundException("ID not found"));
// Throws custom exception if Optional is empty

• Tip: Use lambda-supplied exceptions for lazy initialization.
• Real Use: Validating mandatory fields in REST API requests.

4. Side-Effect-Free Operations

Optional<Integer> price = Optional.of(100);
price.ifPresent(p -> System.out.println("Total: $" + p * 1.1));
// Executes only if value exists (no side effects)

• Tip: Avoid using get() directly—it’s unsafe.
• Real Use: Logging or sending notifications for non-null values.

5. Flatten Nested Optionals

Optional<Optional<String>> nested = Optional.of(Optional.of("Java"));
String result = nested.flatMap(Function.identity())
.orElse("None");
// flatMap() removes nested Optional layers

• Tip: Use flatMap() when dealing with methods returning Optional.
• Real Use: Chaining repository calls (e.g., findUser().flatMap(User::getAddress)).

💡 Pro Interview Tip

Always prefer Optional over null in method returns. Interviewers often judge candidates on their ability to prevent NullPointerException defensively. Example: Return Optional.empty() instead of null for "not found" scenarios.