Object Class & Constructors

this refers to the current object (my fields, my methods, my other constructor). super refers to the parent class (parent fields, parent overridden method, parent constructor). Constructor calls: this() or super() must be the first line, never both.

A constructor initializes an object on new. It has the same name as the class and no return type. Yes, a constructor can be private: Singleton (one instance), Factory (named creation), Utility (no instance).

Shallow copy copies references (nested objects shared). Deep copy copies everything (nested objects independent). Shallow: change nested in copy, original changes. Deep: change nested in copy, original safe.

instanceof checks type at runtime. Pre-Java-16: check plus explicit cast (two steps). Java 16+: instanceof SavingsAccount sa does check, cast, and bind in one step. Flow-scoped variable. Null-safe.

getClass() returns runtime type. clone() creates a shallow copy (needs Cloneable). wait/notify enables thread communication on the object's monitor (must be in synchronized). finalize() is deprecated (use Cleaner or try-with-resources).