Question 1

What are the key features introduced in Java 17 LTS?

Accepted Answer

Java 17 LTS introduces sealed classes for restricted inheritance, pattern matching for switch (preview), enhanced pseudo-random number generators, and removes deprecated features like the Applet API. It also includes performance improvements, new macOS rendering pipeline, and stronger encapsulation of JDK internals.

Question 2

What is the difference between Java 17 and Java 11 LTS?

Accepted Answer

Java 17 adds sealed classes, pattern matching for switch, records (finalized), text blocks, and improved switch expressions compared to Java 11. It removes deprecated APIs like Applet and Nashorn JavaScript engine, strengthens JDK encapsulation, and includes significant performance improvements and garbage collector enhancements.

Question 3

What are sealed classes in Java 17?

Accepted Answer

Sealed classes restrict which other classes or interfaces may extend or implement them, providing more control over inheritance hierarchies. They enable better domain modeling and exhaustive pattern matching while maintaining type safety by allowing you to specify exactly which classes can extend a parent class using the 'permits' clause.

Question 4

How do you declare a sealed class in Java?

Accepted Answer

You declare a sealed class using the 'sealed' modifier followed by a 'permits' clause listing all classes allowed to extend it. Each permitted subclass must be declared as 'final', 'sealed', or 'non-sealed', and they must be in the same module or package as the sealed parent class.

Question 5

What are record classes in Java and when were they finalized?

Accepted Answer

Record classes are special classes designed to be transparent carriers for immutable data, automatically generating boilerplate code like constructors, equals(), hashCode(), and toString() methods. They were introduced as a preview in Java 14, refined in Java 15, and finalized as a standard feature in Java 16.

Question 6

What is a compact constructor in records?

Accepted Answer

A compact constructor is a special constructor syntax for records that allows you to add validation or normalization logic without explicitly declaring parameters or assignments. Parameters are implicit and field assignments happen automatically after the constructor body executes, making the code more concise and focused on validation.

Question 7

What are the restrictions on record classes?

Accepted Answer

Records are implicitly final and cannot be extended or extend other classes (though they can implement interfaces). They cannot declare additional instance fields beyond their components, and all component fields are implicitly final and private, ensuring immutability and transparent semantics.

Question 8

What is pattern matching for instanceof in Java 17?

Accepted Answer

Pattern matching for instanceof combines type checking and casting into a single operation, automatically creating a pattern variable when the type test succeeds. Instead of separately checking a type with instanceof and then casting, you can declare a pattern variable directly in the instanceof expression that's automatically cast and available in the appropriate scope.

Question 9

What are text blocks in Java and when were they finalized?

Accepted Answer

Text blocks allow multi-line string literals without the need for escape sequences and concatenation, delimited by triple double-quote marks. They were introduced as a preview in Java 13, refined in Java 14, and finalized in Java 15, making it easier to embed JSON, XML, SQL, or HTML directly in Java code.

Question 10

How does indentation work in text blocks?

Accepted Answer

Text blocks automatically strip incidental indentation by determining the minimum indentation across all non-blank lines and removing that amount from each line. The position of the closing delimiter controls the amount of indentation that is removed, allowing you to align text blocks with your code while controlling the actual string content.

Question 11

What is incidental whitespace versus essential whitespace in text blocks?

Accepted Answer

Incidental whitespace is indentation added to align the text block with surrounding code, which is automatically removed by the compiler. Essential whitespace is meaningful whitespace that should be preserved in the final string value, such as formatting within the content itself.

Question 12

What are switch expressions and how do they differ from switch statements?

Accepted Answer

Switch expressions, introduced in Java 14, evaluate to a value and use more concise arrow syntax, unlike traditional switch statements which execute code for side effects. Switch expressions require exhaustiveness (all possible cases must be handled), don't allow fall-through with arrow labels, and eliminate the need for break statements.

Question 13

How do you use arrow labels in switch expressions?

Accepted Answer

Arrow labels (->) in switch expressions provide cleaner syntax that eliminates fall-through behavior and doesn't require break statements. You can use arrows with single expressions, statement blocks with yield, or multiple case labels separated by commas, making code more concise and less error-prone.

Question 14

What is the yield keyword and when do you use it?

Accepted Answer

The yield keyword returns a value from a block of code in switch expressions when you need multiple statements before producing a result. It's required when using code blocks with arrow syntax that contain multiple statements, or when using traditional colon syntax in switch expressions.

Question 15

How do you migrate an application from Java 11 to Java 17?

Accepted Answer

Start by updating Java version in your build tool, then compile and run tests to identify issues. Address strong encapsulation of JDK internals (add --add-opens flags temporarily), remove usage of deprecated APIs, and update dependencies to Java 17-compatible versions. Test thoroughly in staging before production deployment.

Java 17 LTS Overview(4 questions)

What are the key features introduced in Java 17 LTS?

What is the difference between Java 17 and Java 11 LTS?

Why is Java 17 significant as a Long-Term Support release?

How do you migrate an application from Java 11 to Java 17?

Sealed Classes and Interfaces(5 questions)

What are sealed classes and why were they introduced in Java 17?

How do you declare a sealed class in Java?

What is the difference between sealed, non-sealed, and final modifiers?

How do sealed classes enable exhaustive pattern matching?

When should you use sealed classes versus enums?

Records(6 questions)

What are record classes in Java and when were they finalized?

What is a compact constructor in records?

Can records have instance methods and static methods?

What are the restrictions on record classes?

What is the difference between records and traditional POJOs?

How do you validate record components in constructors?

Pattern Matching for instanceof(4 questions)

What is pattern matching for instanceof in Java 17?

How does pattern matching for instanceof simplify type checking?

How does the scope of pattern variables work?

How does pattern matching reduce boilerplate code?

Pattern Matching for switch (Preview)(3 questions)

What is pattern matching for switch introduced as preview in Java 17?

What are guarded patterns in switch?

What is exhaustiveness checking in switch pattern matching?

Text Blocks(4 questions)

What are text blocks in Java and when were they finalized?

How does indentation work in text blocks?

What is incidental whitespace versus essential whitespace?

What are the best practices for using text blocks?

Switch Expressions(4 questions)

What are switch expressions and how do they differ from switch statements?

How do you use arrow labels in switch expressions?

What is the yield keyword and when do you use it?

What is exhaustiveness in switch expressions?

Strong Encapsulation of JDK Internals(3 questions)

What is strong encapsulation of JDK internals in Java 17?

How do you use --add-opens and --add-exports flags?

How do you migrate code that depends on internal JDK APIs?

Foreign Function and Memory API(3 questions)

What is the Foreign Function and Memory API introduced in Java 17?

How does the Foreign Function API compare to JNI?

What is a MemorySegment in the Foreign Memory API?

New APIs and Enhancements(4 questions)

What new methods were added to the String class in Java 17?

What is the HexFormat class introduced in Java 17?

How do you use the new Stream.toList() method?

What improvements were made to NullPointerException messages?

Garbage Collection(3 questions)

What garbage collectors are available in Java 17?

What improvements were made to ZGC in Java 17?

How do you choose between ZGC, G1, and other collectors?

Migration and Best Practices(4 questions)

What are the steps to migrate from Java 8 to Java 17?

What tools help with Java version migration?

What are the best practices for writing modern Java 17 code?

How do you configure Maven/Gradle for Java 17?