Code With Clarity

Expectations from a Core Java Developer
(What companies really look for in interviews)

General Expections

Companies do not expect you to know everything.
They expect you to think clearly.

When interviewers ask tough or new questions, they mainly want to see:

  • Do you try to solve the problem?

  • How do you break a big problem into small parts?

  • What logic or approach do you follow?

  • Do you apply basic design principles?

Open-ended questions

Sometimes questions have no single correct answer.
Here the interviewer checks:

  • How you explain using your past experience

  • Whether you speak with clarity and confidence

If you explain the idea fully and calmly, your chance of selection becomes high.

Ambiguous questions

If the problem is not clear:

  • A good developer asks questions first

  • Then starts solving

👉 Asking questions is a strength, not a weakness


Problem-Solving Skills

Problem-solving questions test your design thinking, not just coding.

Interviewers want to see:

  • Are you trying, or giving up?

  • Can you design a solution, even without full code?

  • Can you explain your thought process?

✔ Even a partial solution with clear thinking is appreciated.


Java Fundamentals

You should clearly understand:

  • Purpose of Java keywords

  • Static vs dynamic binding

  • Rules of method overloading & overriding

  • Exception handling rules

  • equals() and hashCode() default behavior

  • Immutability and its benefits

  • Use of final (performance + security)

  • Cloning basics

👉 Strong fundamentals show that you really know Java, not just syntax.


Data Structures

You should know:

  • Basic data structures and how they work internally

  • When to use List, Set, Map, Queue

  • How HashMap / HashSet work internally

  • Time complexity of operations

  • Resizing, capacity, and load factor

  • Comparable vs Comparator

  • Basic sorting algorithms

You should be able to:

  • Choose the right data structure for a use case

  • Explain how to improve performance

  • Implement one data structure using another

Concurrent API

You should understand:

  • How ConcurrentHashMap works internally

  • Why it is better than Hashtable and synchronized maps

  • What problems BlockingQueue solves

  • Difference between ArrayBlockingQueue and LinkedBlockingQueue

  • Fail-safe iterators

Also know:

  • Thread pools and ExecutorService

  • Parallel and pipeline processing

  • CountDownLatch, CyclicBarrier, Semaphore

  • CAS (Compare And Set) concept

  • How Atomic classes work

Multithreading Basics

You should know:

  • wait(), notify(), sleep(), join()

  • Object lock vs class lock

  • Inter-thread communication

  • volatile and happens-before concept

  • Importance of immutability in multithreading

  • How deadlock and starvation happen

👉 Understanding behavior is more important than memorizing APIs.


Serialization

You should know:

  • Why serialization is used

  • What serialVersionUID is

  • What happens if it is not defined

  • How JVM generates it

  • Custom serialization (readObject, writeObject)

  • Handling transient variables

  • How to improve performance


Memory management

You should understand:

  • Java memory model

  • Heap and Garbage Collection basics

  • Where class metadata is stored

  • Why OutOfMemoryError occurs

  • What was PermGen and why it failed

  • Basic memory profiling ideas

  • How to find memory-heavy code

Design Pattern

You should know 2–3 patterns deeply, not all.

Important ones:

  • Singleton

  • Factory

  • Strategy

  • Builder

  • Decorator

  • Adapter

  • Flyweight

You should:

  • Explain where and why to use them

  • Give real examples

  • Know at least one JDK example


Design Principle

You must understand:

  • SOLID principles

  • Why coding to interface is important

  • How good design makes code:

    • Easy to change

    • Easy to test

    • Easy to maintain


Object oriented Concept

You should clearly know:

  • Encapsulation

  • Inheritance

  • Polymorphism

  • Composition

Most important:

  • When to use inheritance

  • When to prefer composition


Database

You should be able to:

  • Write simple JOIN and GROUP BY queries

  • Understand indexes

  • Know types of keys:

    • Primary

    • Foreign

    • Unique

  • Know how indexing improves performance


Spring

You should know:

  • Dependency Injection (IoC)

  • Autowiring (XML + annotations)

  • Bean lifecycle

  • Profiles

  • Transaction management

  • Externalized configuration


Rest

You should understand:

  • What REST is

  • REST principles (stateless, client-server, cacheable)

  • HTTP methods (GET, POST, PUT, DELETE)

  • Status codes

  • Headers

  • Resources concept



Micro-Services

You should know:

  • What Microservices are

  • Difference between Monolith vs Microservices

  • Advantages of Microservices

  • A small Spring Boot microservice example