Java 11 Interview Questions for Experienced Professionals

Java 11, released in September 2018, introduced several important new features and improvements that every experienced Java developer should be familiar with. In this article, we’ll look at some of the frequently asked Java 11 interview questions for experienced developers. Mastering these concepts will help you stand out in your next Java interview.

Top Java 11 Features to Know

Here are some of the major features and improvements in Java 11 that interviewers commonly ask about:

• Local-Variable Syntax for Lambda Parameters – Allows using var in lambda parameters for brevity and readability. For example (var x var y) -> x + y

• HTTP Client API – A new standardized HTTP client API for performing HTTP requests asynchronously and supporting HTTP/2.

• String New Methods – Useful new methods like isBlank(), lines(), strip(), repeat().

• Optional Class Enhancements – New methods like or(), ifPresentOrElse(), stream() etc.

• Files.readString and writeString – Convenience methods for reading and writing strings from files.

• Nest-Based Access Control – Improved encapsulation of nested classes.

• Epsilon Garbage Collector – A no-op GC for performance testing.

• ZGC Garbage Collector – Low latency scalable garbage collector.

Commonly Asked Java 11 Interview Questions

Here are some of the most frequently asked Java 11 interview questions for experienced developers:

Q1. What are some key features introduced in Java 11?

This tests the candidate’s awareness of the major new features in Java 11. Mention features like:

• Local variable syntax for lambdas
• New HTTP client API
• String methods like isBlank(), lines(), etc
• var keyword for local variable type inference
• Nest-based access control
• ZGC garbage collector
• Deprecation of Nashorn JS engine

Focus on 2-3 major features and benefits in your response.

Q2. How is the var keyword used in Java 11?

var can be used to declare the type of lambda parameters. This enhances brevity and readability. For example:

list.forEach((var item) -> {    // process item});

Emphasize that var is similar to auto in C++ and can only be used for local variable declarations.

Q3. Explain the HTTP Client API in Java 11.

The new HTTP Client API provides a modern way for performing HTTP requests and handling responses. Key points:

• Supports both sync and async modes
• Easy to use fluent API compared to older HttpURLConnection
• Built on reactive streams so performs non-blocking I/O
• Supports HTTP/2 transparently

Provide a code example illustrating usage.

Q4. What are some key String methods added in Java 11?

Cover commonly used methods like:

• isBlank() – returns true if string is empty or only whitespace
• lines() – returns stream of lines from string
• strip(), stripLeading(), stripTrailing() – remove whitespace
• repeat() – repeats string multiple times

Provide 1-2 example usages.

Q5. How can Java 11’s Optional class improvements be useful?

Highlight the new Optional methods and how they help avoid null checks:

• ifPresentOrElse() – perform action if value present, else another action
• or() – returns alternate Optional if empty
• stream() – convert to stream, avoids null checks

Give examples to demonstrate the new methods.

Q6. When would you use the Epsilon GC in Java 11?

Explain that Epsilon GC is a no-op garbage collector – it allocates memory but does no collection. Useful for:

• Performance benchmarking/testing when GC overhead needs to be eliminated
• Memory profiling tools where GC interference needs to be avoided

Also provide an example command line for enabling Epsilon GC.

Q7. How do you read/write strings from files in Java 11?

Java 11 added convenience methods Files.readString() and Files.writeString() for easier file I/O with strings. Key points:

• Avoid boilerplate code with BufferedReader/Writer
• Pass path instead of File object
• Methods handle charset encoding/decoding automatically

Provide examples to demonstrate file string reading and writing.

Q8. What is nest-based access control in Java 11?

Nest-based access control improves encapsulation between nested classes. It allows nested classes to access private members within the outer class.

For example:

public class Outer {    private int x = 10;        class Inner {        public int getX() {            return x; //access private member of Outer        }    }}

Explain how this improves flexibility for nested classes.

Q9. When would you use the ZGC collector introduced in Java 11?

Highlight that ZGC is a scalable low latency garbage collector:

• Handles heaps from hundreds of MB to multi TB
• Aims for max GC pause time of 10ms
• Uses multiple threads and CPUs for GC

Good for applications that require low latency GC pauses.

Q10. How can you migrate from Java 8/9 to Java 11 modules?

Explain the transition tools provided in Java 11:

• --add-modules option to add specific modules
• Unnamed modules automatically created for JARs on classpath
• --limit-modules to limit accessible modules

Emphasize Java 11 helps simplify the migration to modules.