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Easy Questions

  1. What is the new var keyword introduced in Java 11?

    • The var keyword allows local variable type inference. It lets the compiler infer the type of the variable based on the value assigned to it.

  2. How can you run a single Java source file directly from the command line in Java 11?

    • You can use the java command to run a single source file directly. For example: java HelloWorld.java.

  3. What is the difference between String::lines and BufferedReader::lines in Java 11?

    • String::lines returns a stream of lines extracted from the string, whereas BufferedReader::lines returns a stream of lines read from a BufferedReader.

  4. What is the purpose of the isBlank method in the String class?

    • The isBlank method returns true if the string is empty or contains only white space codepoints.

  5. Explain the strip method in the String class.

    • The strip method removes leading and trailing white spaces from the string, including Unicode white spaces.

  6. What is the difference between strip and trim methods in the String class?

    • strip handles Unicode white spaces, while trim only handles ASCII white spaces.

  7. How do you create an immutable collection in Java 11?

    • You can use the List.of, Set.of, or Map.of methods to create immutable collections.

  8. What is the repeat method in the String class used for?

    • The repeat method returns a new string whose value is the concatenation of the original string repeated a specified number of times.

  9. Describe the LocalVariable.get method introduced in Java 11.

    • LocalVariable.get is a method in the LocalVariable class that retrieves the value of the variable.

  10. What enhancements have been made to the Optional class in Java 11?

    • Java 11 introduces the isEmpty method to check if an Optional is empty, and Optional::stream to convert an Optional to a stream.

Medium Questions

  1. Explain the new HttpClient API introduced in Java 11.

    • The new HttpClient API provides a modern and flexible way to perform HTTP requests. It supports synchronous and asynchronous requests, HTTP/2, and WebSocket.

  2. How can you read a file as a string in Java 11?

    • You can use Files.readString(Path path) to read the contents of a file as a string.

  3. What is the purpose of the Predicate.not method?

    • The Predicate.not method is a static method that returns a predicate representing the negation of the specified predicate.

  4. Explain the Collectors::toUnmodifiableList method.

    • Collectors.toUnmodifiableList returns a Collector that accumulates the input elements into an unmodifiable list.

  5. How has the ZGC garbage collector been enhanced in Java 11?

    • ZGC in Java 11 is designed to handle very large heaps (multi-terabyte heaps) with low latency.

  6. What improvements have been made to the Nest-Based Access Control in Java 11?

    • Nest-Based Access Control allows classes that are logically grouped together (nested types) to access each other's private members.

  7. How do you create a new String from bytes using the new methods in Java 11?

    • You can use String(byte[] bytes, int offset, int length) to create a new String from a byte array.

  8. Explain the Files.writeString method introduced in Java 11.

    • Files.writeString(Path path, CharSequence csq) writes the specified string to a file.

  9. What is the purpose of the Key Agreement API introduced in Java 11?

    • The Key Agreement API allows two parties to securely agree on a shared secret key over an insecure channel.

  10. How has the JEP 330: Launch Single-File Source-Code Programs improved Java development?

    • JEP 330 allows developers to run a single Java source file directly without needing to compile it first, simplifying quick prototyping and scripting.
    • JDK Enhancement Proposals

  11. Describe the toArray(IntFunction) method added to the Collection interface.

    • The toArray(IntFunction) method allows the creation of an array of the collection's elements using the provided array generator function.

  12. How does the HttpClient::sendAsync method work?

    • HttpClient::sendAsync sends an HTTP request asynchronously and returns a CompletableFuture that completes with the HttpResponse.

  13. Explain the enhancements in Flight Recorder in Java 11.

    • Flight Recorder in Java 11 is now open-sourced and provides detailed profiling and diagnostic data for Java applications.

  14. What is the Epsilon garbage collector in Java 11?

    • Epsilon is a no-op garbage collector that handles memory allocation without reclamation, intended for performance testing and special use cases where GC overhead is unnecessary.

  15. How do you create an unmodifiable copy of a Map in Java 11?

    • You can use Map.copyOf to create an unmodifiable copy of the given map.

Hard Questions

  1. Explain how the var keyword improves type inference in lambda expressions.

    • The var keyword can be used in lambda parameters to enable type annotations, which can improve readability and allow for annotations.

  2. How does the ZGC garbage collector achieve low-latency performance?

    • ZGC achieves low latency by using a coloring mechanism for pointers and concurrent phases that allow most operations to be non-blocking.

  3. What are the security enhancements in the TLS 1.3 implementation in Java 11?

    • TLS 1.3 improves security with features like zero round-trip time (0-RTT), simplified handshake, and removal of weaker algorithms.

  4. How can the HttpClient API be used to handle WebSocket communication in Java 11?

    • The HttpClient API provides a WebSocket.Builder to create WebSocket clients, allowing for asynchronous communication with WebSocket servers.

  5. Describe the improvements to the Lambda Metafactory in Java 11.

    • The Lambda Metafactory has been optimized for better performance, reducing the overhead of lambda expression creation and execution.

  6. Explain the significance of the dynamic class-file constants (JEP 309) in Java 11.

    • Dynamic class-file constants allow for more flexible and efficient handling of constants in the JVM, improving performance and enabling new features.
    • Dynamic class-file constants is a feature in Java 11 that allows you to define constants in the class file that are determined at runtime. This is in contrast to traditional constants, which are defined at compile time and cannot be changed.

  7. How does the Nest-Based Access Control (JEP 181) enhance encapsulation in Java 11?

    • Nest-Based Access Control allows nested classes to access each other's private members, improving encapsulation and reducing boilerplate code.

  8. What are the advantages of the new compact number formatting in Java 11?

    • Compact number formatting provides a way to format numbers in a more readable, locale-sensitive manner, such as "1K" for 1,000.

  9. How does the HttpClient API handle HTTP/2 features in Java 11?

    • The HttpClient API supports multiplexing, header compression, and server push, all features of HTTP/2, improving performance and efficiency.

  10. What changes have been made to the AArch64 port in Java 11?

    • The AArch64 port has been stabilized and improved for better performance and compatibility on ARM architectures.

  11. Describe how the Switch Expressions (preview feature) can simplify code in Java 11.

    • Switch expressions allow switch statements to return values and be used as expressions, reducing boilerplate and increasing readability.

  12. How do you handle raw string literals in Java 11?

    • Although raw string literals were proposed, they were not included in Java 11. Instead, text blocks were introduced in later versions for multiline strings.

  13. Explain the purpose and usage of the Pattern.compile method with flags in Java 11.

    • Pattern.compile compiles a regular expression with optional flags for case insensitivity, multiline mode, etc., for more flexible pattern matching.

  14. How does the Flight Recorder API help in performance monitoring?

    • Flight Recorder records events and metrics from the JVM and application, providing insights for performance tuning and troubleshooting.

  15. Describe the impact of JEP 321: HTTP Client on legacy HttpURLConnection code.

    • The new HttpClient API replaces the legacy HttpURLConnection, offering a more modern, flexible, and performant way to handle HTTP requests.

  16. What are the key benefits of the String::strip family of methods?

    • strip, stripLeading, and stripTrailing provide efficient and Unicode-aware trimming of whitespace characters.

  17. How can Stack-Walking API in Java 11 be used for better performance in stack trace analysis?

    • The Stack-Walking API provides a flexible and efficient way to traverse and analyze stack frames, improving performance and capabilities for diagnostics.

  18. What improvements have been made to the G1 Garbage Collector in Java 11?

    • Enhancements to the G1 garbage collector include better performance, lower pause times, and improvements to heap region size selection.

  19. Explain how JEP 318: Epsilon is beneficial for certain Java applications.

    • Epsilon is beneficial for performance testing, short-lived jobs, and other scenarios where GC overhead is unnecessary, providing predictable performance.

  20. How does JEP 328: Flight Recorder enhance JVM monitoring?

    • Flight Recorder provides a detailed and low-overhead event-based profiling and diagnostics framework, aiding in performance tuning and troubleshooting.

  21. Describe the concept of Key Agreement and its implementation in Java 11.

    • Key Agreement allows two parties to securely agree on a shared secret key using algorithms like Diffie-Hellman, providing secure communication channels.

  22. What are the improvements in Nashorn in Java 11?

    • Although Nashorn was deprecated for removal, improvements included better ES6 support and performance optimizations.

  23. Explain the role of java.lang.invoke in supporting dynamic languages on the JVM.

    • java.lang.invoke provides low-level primitives for efficient method handle-based invocation, supporting dynamic language features on the JVM.

  24. How does the ConstantDynamic feature (JEP 309) enhance JVM capabilities?

    • ConstantDynamic allows constants to be computed at runtime, providing more flexibility and efficiency in class file constant handling.

  25. What are the benefits of the GC Interface introduced in Java 11?

    • The GC Interface allows for better isolation and modularization of garbage collectors, enabling easier experimentation and development of new GCs.

  26. Explain the improvements made to JEP 329: ChaCha20 and Poly1305 Cryptographic Algorithms.

    • These algorithms provide high-performance, secure encryption and authentication, enhancing Java's cryptographic capabilities.

  27. How does the java.util.concurrent package in Java 11 improve concurrency handling?

    • Improvements include better performance, additional utility methods, and enhancements to existing concurrency constructs for better scalability.

  28. Describe the enhancements in Dynamic Class-File Constants (JEP 309).

    • These enhancements improve performance and flexibility in constant pool handling, allowing for more dynamic and efficient constant resolution.

  29. How has the Class-Data Sharing feature been improved in Java 11?

    • Class-Data Sharing now supports application classes, reducing startup time and memory footprint by sharing common class metadata across JVM instances.

  30. What are the key security updates in Java 11?

    • Security updates include TLS 1.3 support, improvements to the default cryptographic algorithms, and enhancements to the Java security manager.