Java Backend Developer: Free Skill Evaluation

Software Development Fundamentals Programming Logic Problem Solving Complexity Awareness Java Platform Java Program Structure Variables Primitive Types Reference Types Operators Type Conversion Input / Output Conditions Loops Arrays Methods Scope Recursion Classes Objects Constructors Encapsulation Inheritance Polymorphism Abstraction Interfaces Abstract Classes Composition Association Immutability SOLID Fundamentals Object Object Identity vs Equality Immutable Objects Records Enums Wrapper Classes Autoboxing String String Pool String Immutability StringBuilder StringBuffer Regular Expressions Common String Interview Problems Exception Hierarchy Checked Exceptions Runtime Exceptions try/catch/finally throw / throws Custom Exceptions Exception Translation Error Handling Principles Collection Architecture ArrayList LinkedList HashSet TreeSet HashMap LinkedHashMap TreeMap Queue PriorityQueue Deque Iterator Comparable Comparator HashMap Internals Concurrent Collections Generic Classes Generic Methods Bounds Wildcards PECS Concept Functional Interfaces Lambda Expressions Predicate Function Consumer Supplier Method References Stream Fundamentals map() flatMap() filter() reduce() collect() groupingBy() partitioningBy() Sorting Parallel Streams var Sealed Classes Pattern Matching Modern Switch Text Blocks Optional Date/Time API Virtual Threads Process vs Thread Thread Lifecycle Runnable Callable Synchronization Race Conditions Visibility volatile Locks Deadlocks Atomic Classes ExecutorService Thread Pools Future CompletableFuture ConcurrentHashMap BlockingQueue JVM Architecture Class Loading Heap Stack Metaspace Object Allocation Garbage Collection GC Algorithms Concepts Stop-The-World Events Memory Leaks OutOfMemoryError StackOverflowError Thread Dumps Heap Dumps JVM Options Profiling Concepts JFR / diagnostic tooling awareness Maven pom.xml Dependency Management Plugins Maven Lifecycle Profiles Multi-Module Builds Dependency Conflicts Gradle Awareness Repository Commit Branch Merge Rebase Concepts Conflict Resolution Pull Requests Code Reviews Release Tags Relational Model Keys Constraints Normalization Denormalization Transactions ACID Isolation Levels CRUD SQL Joins Aggregation Subqueries CTEs Window Functions Indexes Composite Indexes Covering Index Concepts Execution Plans Query Optimization Pagination PostgreSQL Architecture Concepts Schemas Index Types Awareness JSON/JSONB Concepts Connection Management Explain / Analyze Concepts JDBC Architecture Connections PreparedStatement ResultSet SQL Injection Prevention Batch Updates Connection Pooling HTTP HTTPS Request/Response Headers Status Codes Content Negotiation Caching Headers Cookies Sessions TLS Concepts REST Resource Modeling HTTP Semantics Request DTO Response DTO Validation Filtering Search API Versioning Idempotency Idempotency Keys Error Response Design Problem Details Concepts API Compatibility OpenAPI Swagger IoC Dependency Injection Beans Component Scanning Configuration Bean Lifecycle Properties Boot Architecture Starters Auto Configuration application.properties YAML Configuration Properties External Configuration Application Startup Embedded Server Logging Actuator Health Indicators DispatcherServlet Controllers RequestMapping PathVariable RequestParam RequestBody ResponseEntity ExceptionHandler ControllerAdvice Filters Interceptors Production Api Project ORM Entity Persistence Context Entity States JPQL Native Queries One-to-One One-to-Many Many-to-One Many-to-Many Fetch Strategies Cascades Orphan Removal N+1 Problem Fetch Joins Entity Graphs Concepts Batch Operations Auditing @Transactional Transaction Boundaries Propagation Isolation Rollback Read-Only Transactions Optimistic Locking Pessimistic Locking Lost Update Problem Deadlock Handling Schema Versioning Flyway Concepts Migration Scripts Backward-Compatible Database Changes Expand/Contract Pattern Concepts Authentication Authorization Security Filter Chain Password Hashing Roles Authorities Method Security CORS CSRF Session Security JWT Access Tokens Refresh Tokens Token Expiry Key Rotation Concepts Revocation Strategies Secure Token Validation OAuth 2.0 OpenID Connect Resource Server OAuth2 Client Authorization Server Concepts Authorization Code PKCE Client Credentials Scopes JWT vs Opaque Tokens OWASP API Risks Input Validation Output Validation Rate Limiting Brute-Force Protection Secrets Secure Headers Audit Logging Sensitive Data Handling Testing Strategy Unit Tests JUnit Assertions Mockito Mocking Controller Testing MockMvc Repository Testing Integration Testing Test Database Strategy Testcontainers Concepts API Contract Testing Concepts Mutation Testing Awareness Test Design Layered Architecture Modular Monolith Hexagonal Architecture Clean Architecture Concepts Ports and Adapters Domain Services Repository Pattern Domain Bounded Context Value Object Aggregate Aggregate Root Domain Events Anti-Corruption Layer Concepts Microservice Architecture Why Microservices? When NOT to Use Microservices Service Boundaries Database Per Service Loose Coupling Independent Deployment Distributed System Complexity Synchronous REST HTTP Clients RestClient WebClient Awareness gRPC Awareness Asynchronous Communication Choosing Sync vs Async Timeout Retry Exponential Backoff Jitter Circuit Breaker Bulkhead Rate Limiter Resilience4j Fallback Duplicate Requests Idempotent Consumers Duplicate Event Detection Retry-Safe Business Logic Distributed Transaction Problem Two-Phase Commit Concepts Saga Choreography Orchestration Compensation Transactional Outbox Inbox Pattern Concepts Event-Driven Systems Kafka Architecture Brokers Topics Partitions Producers Consumers Consumer Groups Offsets Ordering Replication Delivery Semantics Serialization Schema Evolution Retry Topics Dead-Letter Topics Consumer Lag Idempotent Consumer Caching Fundamentals Cache-Aside Write-Through Concepts TTL Cache Eviction Cache Invalidation Cache Stampede Distributed Locks Concepts Session Storage Concepts Gateway Pattern Routing Header Manipulation Correlation IDs Spring Cloud Gateway Concepts Central Configuration Service Discovery Concepts Kubernetes DNS / Service Discovery Environment-Based Configuration Secret Management Scheduled Jobs Asynchronous Jobs Job States Distributed Scheduler Concepts WebSockets Server-Sent Events Notifications Streaming API Concepts Logging Levels Structured Logging JSON Logs Request IDs MDC Concepts Sensitive Data Redaction Operational Metrics Spring Boot Actuator Micrometer Concepts Prometheus Concepts Grafana Concepts Trace Span Context Propagation OpenTelemetry Performance Methodology Latency Percentiles Throughput CPU Bottlenecks Memory Bottlenecks Thread Pool Bottlenecks Database Bottlenecks Network Bottlenecks Slow Queries Query Plans N+1 Batch Inserts Pool Exhaustion Read Replicas Concepts Partitioning Concepts Heap Analysis GC Analysis Thread Dump Analysis CPU Profiling Memory Leak Investigation Connection Leak Investigation Performance Test Design Load Stress Spike Soak Testing JMeter/k6 Concepts Containers Images Dockerfile Multi-Stage Builds Ports Environment Variables Volumes Networks Docker Compose Kubernetes Architecture Pods Deployments Services ConfigMaps Readiness Probe Liveness Probe Startup Probe Requests/Limits Autoscaling Concepts Ingress Concepts Rolling Updates Rollbacks Cloud Fundamentals IAM Networking EC2 S3 RDS Load Balancer Auto Scaling CloudWatch Secrets Management Concepts Container Deployment Concepts Managed Kubernetes Awareness High Availability CI CD GitHub Actions Jenkins Concepts Artifact Repositories Deployment Approvals Rolling Blue/Green Canary Feature Flags Concepts Dependency Vulnerabilities Secret Rotation TLS Certificates Audit Trails Least Privilege Service Identity Supply-Chain Awareness Factory Builder Strategy Adapter Decorator Observer Template Method Chain of Responsibility Facade Low-Level Design Requirements Capacity Estimation API Design Database Selection SQL vs NoSQL Caching Load Balancing Horizontal Scaling Partitioning Message Queues Event Streaming CDN Concepts Object Storage Consistency Availability CAP Theorem Eventual Consistency Backpressure Concepts System Design Cases Production Troubleshooting Reactive Principles Backpressure Reactor Concepts Mono Flux Spring WebFlux Blocking vs Non-Blocking When Reactive Architecture Makes Sense Graalvm / Native Image Awareness LLM API Integration Structured Output Tool Calling Concepts Embeddings Concepts RAG Concepts Spring AI Awareness