Java

When initialization is triggered, initialization rules, and examples for a single class and an inheritance hierarchy.

Historical rules and flow for object allocation in the JVM.

Generational collection and historical Serial, Parallel, CMS, and G1 collectors, including CMS/G1 details and comparison.

When a custom class loader is needed, how to implement one with findClass or loadClass, an example, and a reference.

What escape analysis is, how to enable it, optimizations for non-escaping objects, lock elimination, scalar replacement, stack allocation, and references.

Matching young- and old-generation collectors, JVM parameters, and how to choose.

Code, bytecode, explanation, and a proposed solution for object-creation instruction reordering.

Garbage-collection concepts, when GC happens, what gets collected, what GC does, and references.

Object composition, object headers, instance data, padding, and a JOL experiment.

Strong, soft, weak, and phantom references, examples, and WeakHashMap.