Question 1

What are the main features introduced in Java 11?

Accepted Answer

Java 11 introduced HTTP Client API (standardized), local-variable syntax for lambda parameters (var), new String methods (isBlank(), lines(), strip(), repeat()), single-file source code execution, Files.readString()/writeString() methods, and removed Java EE modules. It's the first LTS release after Java 8 under the new six-month release cadence.

Question 2

Why is Java 11 considered a significant LTS release?

Accepted Answer

Java 11 is significant because it's the first Long-Term Support release after Java 8 under Oracle's new six-month release cadence, bridging a three-year gap. It introduced major licensing changes making OpenJDK production-ready and consolidated features from Java 9 and 10, making it the natural migration path for enterprises on Java 8.

Question 3

What is local variable type inference (var) in Java?

Accepted Answer

The var keyword, introduced in Java 10, allows developers to declare local variables without explicitly specifying their type. The compiler infers the type from the initializer expression, reducing boilerplate while maintaining Java's static typing and type safety. Java 11 extended this to lambda parameters for adding annotations.

Question 4

What new String methods were added in Java 11?

Accepted Answer

Java 11 added isBlank() for checking whitespace-only strings, strip()/stripLeading()/stripTrailing() for Unicode-aware whitespace removal, lines() for splitting strings into a stream of lines, and repeat(int) for repeating strings n times. These methods enhance string manipulation and improve code readability.

Question 5

What is the difference between strip() and trim() in Java 11?

Accepted Answer

The strip() method uses Character.isWhitespace() to remove all Unicode whitespace characters, while trim() only removes characters with code points ≤ U+0020 (space). This means strip() properly handles modern Unicode whitespace like non-breaking spaces, while trim() may miss them.

Question 6

How do you use the lines() method to process multi-line strings?

Accepted Answer

The lines() method returns a Stream<String> of lines extracted from a string, split by line terminators (
, , or 
). You can use Stream operations like filter(), map(), forEach(), or collect() to process lines functionally, making it ideal for parsing text files or processing multi-line content.

Question 7

What is the new HTTP Client API introduced in Java 11?

Accepted Answer

The HTTP Client API (java.net.http) is a modern, standardized API that replaces HttpURLConnection. It provides native HTTP/2 and WebSocket support, synchronous and asynchronous programming with CompletableFuture, and a fluent builder pattern for creating HTTP requests and clients.

Question 8

How do you send synchronous and asynchronous HTTP requests?

Accepted Answer

Use the send() method for synchronous requests that block until the response is received. Use sendAsync() for asynchronous requests that return a CompletableFuture, enabling non-blocking concurrent operations. Asynchronous requests improve resource utilization and are ideal for high-throughput applications.

Question 9

What are collection factory methods in Java 9?

Accepted Answer

Java 9 introduced of() and ofEntries() factory methods on List, Set, and Map interfaces to create immutable collections directly. These methods provide a concise syntax like List.of("A", "B", "C") and create truly immutable collections that don't allow null elements and throw UnsupportedOperationException on modification attempts.

Question 10

How do you run a single-file Java program without compilation?

Accepted Answer

Java 11 introduced the ability to run single-file Java programs directly using java MyProgram.java without explicitly compiling with javac first. The JVM compiles the source code in memory and runs it immediately, streamlining development for simple programs, scripts, and learning exercises.

Question 11

What is the purpose of Files.readString() and Files.writeString()?

Accepted Answer

These convenience methods introduced in Java 11 simplify reading and writing text files in a single line of code. Files.readString() reads entire file contents into a String, while Files.writeString() writes a String to a file, eliminating the need for BufferedReader/Writer boilerplate code.

Question 12

What is the Predicate.not() method in Java 11?

Accepted Answer

Predicate.not() is a static method that creates a negated version of a given predicate. It improves code readability in stream operations by allowing you to write Predicate.not(String::isBlank) instead of s -> !s.isBlank(), making functional code more declarative and easier to read.

Question 13

What is Nest-Based Access Control in Java 11?

Accepted Answer

Nest-Based Access Control (JEP 181) is a JVM feature that allows nested classes to access each other's private members without synthetic bridge methods. This improves performance, reduces bytecode size, enhances security, and makes reflection more predictable when dealing with nested classes.

Question 14

What deprecated features were removed in Java 11?

Accepted Answer

Java 11 removed Java EE and CORBA modules (JAXB, JAX-WS, etc.), JavaFX (moved to separate project), and tools like appletviewer and javapackager. The Nashorn JavaScript engine was deprecated for removal. Applications must now include these as separate dependencies from third-party sources.

Question 15

Can you use var with lambda expressions in Java?

Accepted Answer

You cannot use var to declare a variable holding a lambda without a target type. However, Java 11 allows var in lambda parameter declarations to add annotations while maintaining type inference, like (@NonNull var s) -> {...}, which is useful for null-checking frameworks and code analyzers.

Java 11 Fundamentals(4 questions)

What are the main features introduced in Java 11?

Why is Java 11 considered a significant LTS release?

What features were introduced between Java 8 and Java 11 (Java 9, 10, 11)?

What is the difference between Oracle JDK and OpenJDK starting from Java 11?

Local Variable Type Inference (var)(5 questions)

What is local variable type inference (var) introduced in Java 10?

What are the rules and restrictions for using var?

Can you use var with lambda expressions?

What are the best practices for using var?

When should you avoid using var for readability?

String API Enhancements(5 questions)

What new String methods were added in Java 11?

How do isBlank(), strip(), stripLeading(), and stripTrailing() work?

What is the difference between strip() and trim()?

How do you use the lines() method to process multi-line strings?

What does the repeat() method do?

Collection Factory Methods(4 questions)

What are the collection factory methods introduced in Java 9?

How do you create immutable lists, sets, and maps using of() methods?

What is the difference between Collections.unmodifiableList() and List.of()?

What happens when you try to modify an immutable collection?

Optional API Enhancements(5 questions)

What new methods were added to Optional in Java 9, 10, and 11?

How do you use ifPresentOrElse() method?

What is the or() method in Optional?

How do you convert Optional to a Stream using stream()?

What is orElseThrow() without arguments?

HTTP Client API(5 questions)

What is the new HTTP Client API introduced in Java 11?

How do you send synchronous and asynchronous HTTP requests?

How do you handle HTTP/2 with the new HTTP Client?

How do you configure timeouts and redirects in HTTP Client?

What is the difference between the old HttpURLConnection and the new HttpClient?

Module System (Project Jigsaw)(6 questions)

What is the Java Platform Module System (JPMS) introduced in Java 9?

What is module-info.java and how do you define a module?

What are the keywords exports, requires, opens, and uses in modules?

What is the difference between classpath and module path?

How do you migrate a legacy application to use modules?

What are automatic modules and unnamed modules?

Stream API Enhancements(4 questions)

What new Stream methods were added in Java 9?

How do takeWhile() and dropWhile() work?

What does Stream.ofNullable() do?

How do you use iterate() with a predicate for termination?

Other Java 11 Features(7 questions)

What is the purpose of the Files.readString() and Files.writeString() methods?

What is the Predicate.not() method?

What is the Pattern.asMatchPredicate() method?

How do you run a single-file Java program without compilation in Java 11?

What is the Nest-Based Access Control in Java 11?

What deprecated features were removed in Java 11?

What is the Flight Recorder and how was it made available in Java 11?

Migration and Compatibility(4 questions)

What are the challenges of migrating from Java 8 to Java 11?

How do you handle removed APIs like Java EE modules (JAXB, JAX-WS)?

What tools help analyze compatibility issues when upgrading to Java 11?

How do you use the --add-modules and --add-opens flags?