What is Java?

Java is a general-purpose, class-based language created for portable, maintainable software. It powers Spring Boot microservices, large banking systems, Hadoop-era data tooling, and still underpins much Android history (Kotlin interoperates on the same JVM).

Core characteristics

• Static typing — types checked at compile time; fewer runtime surprises than dynamic languages
• Bytecode + JVM — source compiles to .class files; the JVM JIT-compiles hot paths
• Garbage collection — memory reclaimed automatically; tune GC in production, not in hello-world
• Rich standard library — collections, concurrency, I/O, networking, time API (java.time)

Typical build-run flow

1. Write Main.java with a public class matching the filename
2. javac Main.java produces Main.class
3. java Main starts the JVM and calls main

Important interview questions and answers

1. Q: Is Java compiled or interpreted?
   A: Both—javac compiles to bytecode; the JVM interprets and JIT-compiles to native code at runtime.
2. Q: What is the JVM?
   A: The runtime that loads bytecode, manages memory, and provides platform abstraction.
3. Q: Java vs JavaScript?
   A: Unrelated languages despite the name—Java is statically typed and JVM-based; JavaScript is dynamic and runs in browsers/Node.

Self-check

1. What file extension do Java source files use?
2. Name one industry domain where Java is common.