Java and OOP concepts for quick interview prep.

Develop understanding of class and objects, encapsulation with getters and setters, and access modifiers in Java. Explore packages, constructors, main methods, and basic inheritance from the object class.

Explore key oop concepts like inheritance, encapsulation, abstraction, and polymorphism, including how abstract classes and interfaces define behavior, while encapsulation hides data with private variables and public getters and setters.

Explore single and multilevel inheritance, and understand why Java does not support multiple inheritance, with base and derived classes forming the inheritance hierarchy.

Explore Java scope and access modifiers, including private, default (package-private), protected, and public, and how inheritance affects accessibility across packages and within the same package.

Explore encapsulation in Java by guarding private data with public accessors, controlling modification from outside the class, and binding data with its methods to ensure safe, controlled updates.

Abstract classes cannot be instantiated and must be extended by subclasses. They declare abstract methods with no body, implemented by subclasses, while concrete methods may have bodies, like interface defaults.

Explore how interfaces define constants, support multiple inheritance, and host default methods. Learn how the diamond problem creates ambiguity and how the scope resolution operator resolves it.

Explore polymorphism in Java and oop concepts by examining compile-time polymorphism through method and constructor overloading, and runtime polymorphism via method overriding in base and derived classes.

Learn how a functional interface has one method, can include default methods, and implement it with lambda expressions, using an annotation to mark the interface as functional.

Explore lambda expressions with functional interfaces that have a single abstract method, enabling concise one-argument implementations like printing hello name, and understand why adding methods breaks the interface.

Explore Java's data structures, including the collection framework, list and map interfaces with their implementations, linked lists, sets, and queues; learn index-based storage, unique keys, and fast key lookup.

Learn to implement equals and hashCode to compare objects, ensuring equal objects share the same hashCode and that equality relies on fields like name and id.

Explore the List interface and its implementations, including LinkedList and ArrayList, and learn key operations like add, addAll, contains, and equals, plus when index-based access is faster.

Explore how comparable and comparator enable flexible object comparison in Java, using a person class with different comparators for name, or name and age, while comparable offers a single criterion.

Explore Java maps, including hash map, linked hash map, and tree map, with generics and key retrieval. Study how equals and hashCode prevent duplicates and how comparator enables sorting.

Learn how a set enforces uniqueness by equals (and hashCode) to reject duplicates. See how linked, hash, and tree sets manage order with comparator or comparable.

Explore the Java stream API, from source data to intermediate operations and terminal results, using filter, map, sort, collect, and parallel streams to transform collections efficiently.

Master Java multithreading by creating threads with thread and runnable interfaces, using lambda expressions, and coordinating tasks with join, synchronization, and an executor service.