The Programmer's Guide
  • About
  • Algorithm
    • Big O Notation
      • Tree
      • Problems
    • Basic Notes
    • Data Structure Implementation
      • Custom LinkedList
      • Custom Stack
      • Custom Queue
      • Custom Tree
        • Binary Tree Implementation
        • Binary Search Tree Implementation
        • Min Heap Implementation
        • Max Heap Implementation
        • Trie Implementation
      • Custom Graph
        • Adjacency List
        • Adjacency Matrix
        • Edge List
        • Bidirectional Search
    • Mathematical Algorithms
      • Problems - Set 1
      • Problems - Set 2
    • Bit Manipulation
      • Representation
      • Truth Tables
      • Number System
        • Java Program
      • Problems - Set 1
    • Searching
    • Sorting
    • Array Algorithms
    • String Algorithms
    • Tree
      • Tree Traversal Techniques
      • Tree Implementation
      • Applications of Trees
      • Problems - Set 1
    • Graph
      • Graph Traversal Techniques
      • Shortest Path Algorithms
      • Minimum Spanning Tree (MST) Algorithms
    • Dynamic Programming
      • Problems - Set 1
    • Recursion
    • Parallel Programming
    • Miscellaneous
      • Problems - Set 1
  • API
    • API Basics
      • What is an API?
      • Types of API
        • Comparison - TBU
      • Synchronous vs Asynchronous API
    • API Architecture
      • Synchronous & Asynchronous Communication
    • API Specification
      • OpenAPI - TBD
    • API Design Principles - TBU
      • RESTful API Principles
      • Rate Limiting & Pagination - TBU
      • Idempotency & Statelessness - TBU
    • API Security & Authentication - TBU
      • OAuth 2.0, JWT, API Keys - TBU
      • Rate Limiting & Throttling - TBU
      • CORS in API - TBU
    • REST API - TBD
      • HTTP Status Code
      • HTTP Verbs or Methods
      • HTTP Headers
      • Query Parameters & Path Parameters - TBU
      • Content Types - TBU
  • Cloud Computing
    • Cloud Fundamentals
      • Cloud Terminology
      • Core Terminology
      • Cloud Models
      • Cloud Service Models
      • Benefits, Challenges and Risk of Cloud Computing
      • Cloud Ecosystem
  • Database
    • DBMS
      • Types of DBMS
        • Relational DBMS (RDBMS)
        • NoSQL DBMS
        • Object-Oriented DBMS (OODBMS)
        • Columnar DBMS
        • In-Memory DBMS
        • Distributed DBMS
        • Cloud-Based DBMS
        • Hierarchical DBMS
      • DBMS Architecture
      • DBMS Structure
    • SQL Databases
      • Terminology
      • RDBMS Concepts
        • Entity Relationship Diagram (ERD)
          • ERD Examples
        • Normalization
        • Denormalization
        • ACID & BASE Properties
          • ACID Properties
          • BASE Properties
      • SQL Fundamentals
        • SQL Commands
          • DDL (Data Definition Language)
          • DML (Data Manipulation Language)
          • DCL (Data Control Language)
          • TCL (Transaction Control Language)
          • DQL (Data Query Language)
        • SQL Operators
          • INTERSECT
          • EXCEPT
          • MINUS
          • IN and NOT IN
          • EXISTS and NOT EXISTS
        • SQL Clauses
          • Joins
          • OVER
          • WITH
          • CONNECT BY
          • MODEL
          • FETCH FIRST
          • KEEP
          • OFFSET with FETCH
        • SQL Functions
          • Oracle Specific
        • Others
          • Views
          • Indexing - TBU
          • Transactions - TBU
          • Triggers - TBU
      • Vendor-Specific Concepts
        • Oracle Specific
          • Rownum vs Rowid
          • Order of Execution of the query
          • Keys
          • Tablespace
          • Partition
      • Best Practice
      • Resources & References
        • O’Reilly SQL Cookbook (2nd Edition)
          • 1. Retrieving Records
          • 2. Sorting Query Results
          • 3. Working with Multiple Tables
          • 4. Inserting, Updating, and Deleting
          • 5. Metadata Queries
          • 6. Working with Strings
          • 7. Working with Numbers
          • 8. Date Arithmetic
          • 9. Date Manipulation
          • 10. Working with Ranges
          • 11. Advanced Searching
          • 12. Reporting and Reshaping
          • 13. Hierarchical Queries
          • 14. Odds 'n' Ends
    • NoSQL Databases -TBU
      • Concepts
      • Types of NoSQL
        • Document Stores
        • Key-Value Stores
        • Column-Family Stores
        • Graph Databases
    • SQL vs NoSQL
    • Best Practices
  • Git
    • Internals of Git [TBD]
    • Commands
      • Setup and Configuration Commands
      • Getting and Creating Projects
      • Tracking Changes
      • Branching and Merging
      • Sharing and Updating Projects
      • Inspection and Comparison
      • Debugging
      • Patching
      • Stashing and Cleaning
      • Advanced Manipulations
      • Other Commands
    • Workflows
  • Java
    • Java Installation
    • Java Overview
      • OOP Principles
        • Encapsulation
        • Inheritance
        • Polymorphism
        • Abstraction
          • Abstract Class & Method
          • Interface
            • Functional Interfaces
            • Marker Interfaces
          • Abstract Class vs Interface
      • OOP Basics
        • What is a Class?
          • Types of Classes
        • What is an Object?
          • Equals and HashCode
            • FAQ
          • Shallow Copy and Deep Copy
          • Ways to Create Object
          • Serialization & Deserialization
        • Methods & Fields
          • Method Overriding & Overloading
          • Method Signature & Header
          • Variables
        • Constructors
        • Access Modifiers
      • Parallelism and Concurrency
        • Ways to Identify Thread Concurrency or Parallelism
        • Thread Basics
          • Thread vs Process
          • Creating Threads
          • Thread Context Switching
          • Thread Lifecycle & States
          • Runnable & Callable
          • Types of Threads
          • Thread Priority
        • Thread Management & Synchronisation
          • Thread Resource Sharing
          • Thread Synchronization
            • Why is Synchronization Needed?
            • Synchronized Blocks & Methods
          • Thread Lock
            • Types of Locks
            • Intrinsic Lock (Monitor Lock)
            • Reentrant Lock
          • Semaphore
          • Thread Starvation
          • Thread Contention
          • Thread Deadlock
          • Best Practices for Avoiding Thread Issues
      • Keywords
        • this
        • super
        • Access Modifiers
      • Data Types
        • Default Values
        • Primitive Types
          • byte
          • short
          • int
          • long
          • float
          • double
          • char
          • boolean
        • Non-Primitive (Reference) Types
          • String
            • StringBuilder
            • StringBuffer
              • Problems
            • Multiline String
            • Comparison - String, StringBuilder & StringBuffer
          • Array
          • Collections
            • List
              • Array vs List
              • ArrayList
              • Vector
                • Stack
                  • Problems
              • LinkedList
            • Queue
              • PriorityQueue
              • Deque (Double-Ended Queue)
                • ArrayDeque
                • ConcurrentLinkedDeque - TBU
                • LinkedBlockingDeque - TBU
            • Map
              • HashMap
              • Hashtable
              • LinkedHashMap
              • ConcurrentHashMap
              • TreeMap
              • EnumMap
              • WeakHashMap
            • Set
              • HashSet
              • LinkedHashSet
              • TreeSet
              • EnumSet
              • ConcurrentSkipListSet
              • CopyOnWriteArraySet
        • Specialized Classes
          • BigInteger
          • BigDecimal
            • Examples
          • BitSet
          • Date and Time
            • Examples
          • Optional
          • Math
          • UUID
          • Scanner
          • Formatter
            • Examples
          • Properties
          • Regex (Pattern and Matcher)
            • Examples
          • Atomic Classes
          • Random
          • Format
            • NumberFormat
            • DateFormat
            • DecimalFormat
        • Others
          • Object
          • Enum
            • Pre-Defined Enum
            • Custom Enum
            • EnumSet and EnumMap
          • Record
          • Optional
          • System
          • Runtime
          • ProcessBuilder
          • Thread and ThreadGroup - TBU
          • Class
          • Void
          • Throwable
            • Error
            • Exception
              • Custom Exception Handling
              • Best Practice
            • Error vs Exception
            • StackTraceElement
          • Logger - TBU
          • ResourceBundle - TBU
    • Java Features by Version
      • How New Java Features are Released ?
      • Java Versions
        • Java 8
        • Java 9
        • Scoped Values
        • Unnamed Variables & Patterns
      • Java Distributions
      • FAQ
    • Concepts
      • Set 1
        • Streams
          • flatmap
          • Collectors Utility Class
          • Problems
        • Functional Interfaces
          • Standard Built-In Interfaces
          • Custom Interfaces
        • Annotation
          • Custom Annotation
          • Meta Annotation
        • Generics
          • Covariance and Invariance
        • Asynchronous Computation
          • Future
          • CompletableFuture
          • Future v/s CompletableFuture
          • ExecutorService
            • Thread Pool
            • Types of Work Queues
            • Rejection Policies
            • ExecutorService Implementations
            • ExecutorService Usage
          • Locks, Atomic Variables, CountDownLatch, CyclicBarrier - TBU
          • Parallel Streams, Fork/Join Framework,Stream API with Parallelism - TBU
      • Set 2
        • ISO Standards
        • Localization - TBD
        • Operator Precedence
      • Set 3
        • Date Time Formatter
      • Set 4
        • Input from User
        • Comparison & Ordering
          • Object Equality Check
          • Comparable and Comparator
            • Comparator Interface
          • Sorting of Objects
          • Insertion Ordering
    • Core Packages
      • java.lang
        • java.lang.System
        • java.lang.Thread
    • Code Troubleshoot
      • Thread Dump
      • Heap Dump
    • Code Style
      • Naming Convention
    • Tools
      • IntelliJ IDEA
        • Shortcuts for MAC
      • Apache JMeter
        • Examples
      • Thread Dump Capture
        • jstack
        • VisualVM - TBU
        • jcmd - TBU
        • JConsole - TBU
        • YourKit Java Profiler - TBU
        • Eclipse MAT - TBU
        • IntelliJ IDEA Profiler - TBU
        • AppDynamics - TBU
        • Dynatrace - TBU
        • Thread Dump Analyzers - TBU
      • Heap Dump Capture
        • jmap
        • VisualVM - TBU
        • jcmd - TBU
        • Eclipse MAT (Memory Analyzer Tool) - TBU
        • IntelliJ IDEA Profiler - TBU
        • YourKit Java Profiler - TBU
        • AppDynamics - TBU
        • Dynatrace - TBU
        • Kill -3 Command - TBU
        • jhat (Java Heap Analysis Tool) - TBU
        • JVM Options - TBU
      • Wireshark
        • Search Filters
    • Best Practices
      • Artifact and BOM Versioning
  • Maven
    • Installation
    • Local Repository & Configuration
    • Command-line Options
    • Build & Lifecycle
    • Dependency Management
      • Dependency
        • Transitive Dependency
        • Optional Dependency
      • Dependency Scope
        • Maven Lifecycle and Dependency Scope
      • Dependency Exclusions & Overrides
      • Bill of Materials (BOM)
      • Dependency Conflict Resolution
      • Dependency Tree & Analysis
      • Dependency Versioning Strategies
    • Plugins
      • Build Lifecycle Management
      • Dependency Management
      • Code Quality and Analysis
      • Documentation Generation
      • Code Generation
      • Packaging and Deployment
      • Reporting
      • Integration and Testing
      • Customization and Enhancement
        • build-helper-maven-plugin
        • properties-maven-plugin
        • ant-run plugin
        • exec-maven-plugin
        • gmavenplus-plugin
      • Performance Optimization
    • FAQs
      • Fixing Maven SSL Issues: Unable to Find Valid Certification Path
  • Spring
    • Spring Basics
      • What is Spring?
      • Why Use Spring
      • Spring Ecosystem
      • Versioning
      • Setting Up a Spring Project
    • Core Concepts
      • Spring Core
        • Dependency Injection (DI)
        • Stereotype Annotation
      • Spring Beans
        • Bean Lifecycle
        • Bean Scope
          • Singleton Bean
        • Lazy & Eager Initialization
          • Use Case of Lazy Initialization
        • BeanFactory
        • ApplicationContext
      • Spring Annotations
        • Spring Boot Specific
        • Controller Layer (Web & REST Controllers)
        • Service Layer (Business Logic)
        • Repository Layer (Data Access)
        • Dependency Injection & Configuration
        • Validation & Binding
        • Caching
        • AOP (Aspect-Oriented Programming)
        • Scheduling
        • Testing - TBU
        • Security
    • Spring Features
      • Spring Caching
        • In-Memory Caching
      • Spring AOP
        • Before Advice
        • After Returning Advice
        • After Throwing Advice
        • After (finally) Advice
        • Around Advice
      • Spring File Handling
        • Apache Camel - TBU
          • Local Docker Setup for SFTP Server
      • Reactive Programming
        • Reactive System
        • Reactive Stream Specification
        • Project Reactor
          • Mono & Flux
      • Asynchronous Computation
        • @Async annotation
        • Context Propagation - TBU
      • Spring Security
        • Authentication
          • Core Components
            • Security Filter Chain
              • HttpSecurity
              • Example
            • AuthenticationManager
            • AuthenticationProvider
            • UserDetailsService
              • UserDetails
              • PasswordEncoder
            • SecurityContext
            • SecurityContextHolder
            • GrantedAuthority
            • Security Configuration (Spring Security DSL)
          • Authentication Models
            • One-Way Authentication
            • Mutual Authentication
          • Authentication Mechanism
            • Basic Authentication
            • Form-Based Authentication
            • Token-Based Authentication (JWT)
            • OAuth2 Authentication
            • Multi-Factor Authentication (MFA)
            • SAML Authentication
            • X.509 Certificate Authentication
            • API Key Authentication
            • Remember-Me Authentication
            • Custom Authentication
          • Logout Handling
        • Authorization
        • Security Filters and Interceptors
        • CSRF
          • Real-World CSRF Attacks & Prevention
        • CORS
        • Session Management and Security
        • Best Practices
      • Spring Persistence
        • JDBC
          • JDBC Components
          • Best Practices in JDBC Usage
        • JPA (Java Persistence API)
          • JPA Fundamentals
          • ORM Mapping Annotations
            • 1. Entity and Table Mappings
            • 2. Field/Column Mappings
            • 3. Relationship Mappings
            • 4. Inheritance Mappings
            • 5. Additional Configuration Annotations
          • Querying Data
            • JPQL
            • Criteria API
            • JPA Specification
              • Example - Employee Portal
            • Native SQL Queries
            • Named Queries
            • Query Return Types
            • Pagination & Sorting
              • Example - Employee Portal
            • Projection
          • Fetch Strategies in JPA
        • JPA Implementation
          • Hibernate
            • Properties
            • Example
        • Spring Data JPA
          • Repository Abstractions
          • Entity-to-Table Mapping
          • Derived Query Methods
        • Examples
          • Employee Portal
    • Distributed Systems & Communication
      • Distributed Scheduling
      • Distributed Tracing
      • Inter-Service Communication
        • 1. RestTemplate
        • 2. WebClient
        • 3. OpenFeign
        • Retry Mechanism
          • @Retryable annotation
            • Example
    • Security & Data Protection
      • Encoding | Decoding
        • Types
          • Base Encoding
            • Base16 - TBD
              • Encoding and Decoding in Java - TBD
            • Base32
              • Encoding and Decoding in Java
            • Base64 -TBD
              • Encoding and Decoding in Java - TBD
          • Text Encoding - TBD
            • Extended ASCII
              • Encoding and Decoding in Java - TBD
                • ISO-8859-1
                • Windows-1252 - TBD
                • IBM Code Pages - TBD
            • ASCII
              • Encoding and Decoding in Java
        • Java Guidelines
          • Text Encoding Decoding Examples
          • Base Encoding Decoding Examples
          • Best Practices and Concepts
          • Libraries
      • Cryptography
        • Terminology
        • Java Cryptography Architecture (JCA)
        • Key Management
          • Key Generation
            • Tools and Libraries
              • OpenSSL
              • Java Keytool
                • Concept
                • Use Cases
            • Key & Certificate File Formats
          • Key Distribution
          • Key Storage
          • Key Rotation
          • Key Revocation
        • Encryption & Decryption
          • Symmetric Encryption
            • Algorithm
            • Modes of Operation
            • Examples
          • Asymmetric Encryption
            • Algorithm
            • Mode of Operation
            • Examples
    • Utilities & Libraries
      • Apache Libraries
        • Apache Camel
          • Camel Architecture
            • Camel Context
            • Camel Endpoints
            • Camel Components
            • Camel Exchange & MEP
          • Spring Dependency
          • Different Components
            • Camel SFTP
        • Apache Commons Lang
      • MapStruct Mapper
      • Utilities by Spring framework
        • FileCopyUtils
    • General Concepts
      • Spring Boot Artifact Packaging
      • Configuration: Mapping Properties to Java Class
    • Best Practice
  • Software Testing
    • Software Testing Methodologies
      • Functional Testing
      • Non Functional Testing
    • Software Testing Life Cycle (STLC)
    • Integration Test
      • Dynamic Property Registration
    • Java Test Framework
      • JUnit
        • JUnit 4
          • Examples
        • JUnit 5
          • Examples
        • JUnit 4 vs JUnit 5
  • System Design
    • Low-Level Design (LLD)
      • Programming Paradigms
      • Design Pattern
        • Creational Pattern
        • Structural Pattern
        • Behavioral Pattern
        • Examples
          • Data Collector
          • Payment Processor
      • Object-Oriented Design
        • SOLID Principles
        • GRASP Principles
        • Composition
        • Aggregation
        • Association
      • Design Enhancements
        • Fluent API Design
          • Examples
    • High-Level Design (HLD)
      • CAP Theorem
      • Load Balancer
        • Load Balancer Architecture
        • Load Balancing in Java Microservices
          • Client-Side Load Balancing Example
          • Server-Side Load Balancing Example
        • Load Balancer Monitoring Tool
      • Architecture
        • Event Driven Architecture
          • Event-Driven Microservices
          • Handling Failures & Retry Mechanisms
          • Event Schema Design (Avro, JSON, Protobuf)
          • Persistence & Non-Persistence Queues
          • Technologies & Frameworks
            • ActiveMQ - TBU
            • Kafka - TBU
      • Scaling
        • Vertical Scaling (Scaling Up)
        • Horizontal Scaling (Scaling Out)
        • Auto-Scaling
        • Database Scaling via Sharding
      • Networking Metrics
        • Types of Delay
        • Scenario
      • System Characteristics
      • Workload Types
      • Resilience & Failure Handling
    • Security
      • Security by Design
      • Zero Trust Security Model
      • Zero Trust Architecture
      • Principles
        • CIA
        • Least Privilege Principle
        • Defense in Depth
      • Security Threats & Mitigations
        • OWASP
          • Top 10 Security Threats
          • Application Security Verification Standard
          • Software Assurance Maturity Model
          • Dependency Check
          • CSRFGuard
          • Cheat Sheets
          • Security Testing Guide
          • Threat Dragon
        • Threat Modeling
      • Compliance & Regulation
        • PCI DSS
    • Deployment Patterns
    • Diagrams
      • UML Diagrams
        • PlantUML
          • Class Diagram
          • Object Diagram
          • Sequence Diagram
          • Use Case Diagram
          • Activity Diagram
          • State Diagram
          • Architecture Diagram
          • Component Diagram
          • Timing Diagram
          • ER Diagram (Entity-Relationship)
          • Network Diagram
    • Common Terminologies
  • Web Communication and Security
    • IT Security
      • IAM (Identity and Access Management)
        • Authentication
        • Keycloak
          • Terminologies
          • Token Verification
    • Server in Java
      • Application Server
      • Web Server
    • User Flows
  • Interview Guide
    • Non-Technical
      • Behavioural or Introductory Guide
      • Project Specific
    • Technical
      • Java Interview Companion
        • Java Key Concepts
          • Set 1
          • Set 2
        • Java Code Snippets
        • Java Practice Programs
          • Set 1 - Maths theory & Pattern
          • Set 2 - Arrays
          • Set 3 - Strings
          • Set 4 - Search
          • Set 5 - Streams and Collection
      • SQL Interview Companion
        • SQL Practice Problems
          • Set 1
      • Spring Interview Companion
        • Spring Key Concepts
          • Set 1 - General
          • Set 2 - Core Spring
        • Spring Code Snippets
      • Application Server
      • Maven
      • Containerized Application
      • Microservices
    • General
      • Applicant Tracking System (ATS)
      • General Interview Preparation Tips - TBU
      • Flowchart - How to Solve Coding Problem?
  • Personal Projects
    • Hackathon
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Subpages provides overview of essential Java concepts, covering different topics, useful for the interview.

Last updated 7 months ago

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  1. Interview Guide
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  3. Java Interview Companion

Java Key Concepts

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