Core Java & JVM Internals

Explain the differences between JDK, JRE, and JVM and their roles in application execution.

Describe the JVM's runtime data areas, class loading mechanism, and execution engine.

Compare String, StringBuilder, and StringBuffer, explaining string immutability and the String pool.

Implement the equals() and hashCode() contract correctly and explain its importance for collections.

Explain the Java Memory Model (JMM), heap structure, and the goals of modern garbage collectors (e.g., G1, ZGC).

Diagnose common JVM errors like OutOfMemoryError and StackOverflowError, and explain their causes.

Explain the difference between primitive types and wrapper classes, including autoboxing and its performance implications.

Explain why Java is pass-by-value, demonstrating with primitive and object reference examples.