Java Interview Questions on Java SE 22

1. What are Unnamed Variables and Patterns and how do they simplify Java code?
   
   Answer:
   Java 22 finalizes support for Unnamed Variables and Patterns (JEP 456). You can use the underscore (_) to omit variable names in contexts where the variable is unused—such as in exception handlers, lambda parameters, or pattern matching, reducing boilerplate and improving readability.
2. What is the Foreign Function and Memory API and why is it significant?
   
   Answer:
   The Foreign Function and Memory API (JEP 454) is finalized in Java 22. It replaces the older JNI by offering a safer, lower-overhead way for Java to call native code and manage off-heap memory (via MemorySegment, Arena, etc.), improving performance and ergonomics.
3. Describe Scoped Values and their advantage over thread-local variables.
   
   Answer:
   Scoped Values (JEP 464, second preview) allow immutable, inheritable values within a confined scope (e.g., a block or thread). They're automatically cleaned up and have better safety and simplicity than traditional thread-local variables.


4. What does Structured Concurrency bring to Java threading?
   
   Answer:
   Structured Concurrency (JEP 462, second preview) simplifies concurrent programming by managing related tasks as structured units (e.g., via StructuredTaskScope), improving readability, error handling, and observability for multithreaded workflows.
5. What are Stream Gatherers?
   
   Answer:
   Stream Gatherers (JEP 461, preview) enable writing custom intermediate stream operations, similar to how collectors work for terminal operations, allowing more flexible stream pipelines.


6. Explain the feature Statements Before super(...) in constructors
   
   Answer:
   JEP 447 (preview) allows executing statements before calling super(...) or this(...) in constructors. This gives developers more flexibility for initialization logic, under controlled constraints.
7. What is Launch Multi-File Source-Code Programs?
   
   Answer:
   JEP 458 enables running Java programs composed of multiple .java files directly—without needing prior compilation. This improves rapid prototyping and simplifies running small multi-file examples.
8. What is the Class-File API introduced in Java 22?
   
   Answer:
   The Class-File API (JEP 457, preview) offers a set of APIs to parse and generate Java .class files programmatically, useful for tools like analyzers, compilers, and bytecode instrumentation utilities.
9. What enhancement does Region Pinning for G1 (JEP 423) provide?
   
   Answer:
   Region Pinning (JEP 423) ensures that G1 garbage collector won't move certain memory regions, especially during JNI critical operations—preventing GC pauses and improving performance in native interactions.
10. Which preview features were carried forward into Java 22 (second preview)?
    
    Answer:
    Java 22 continues the second preview for several features, namely: Structured Concurrency (JEP 462), Scoped Values (JEP 464), String Templates (JEP 459), and Implicitly Declared Classes and Instance Main Methods (JEP 463).