Java Roadmap - Basics -> Advanced -> Java 26

1. Development Environment and Tools

1.1 JDK Installation and Management

• JDK
• JRE
• JVM
• JAVA_HOME
• PATH
• SDKMAN
• jEnv

1.2 Basic JDK Tools

• java
• javac
• jshell
• jar
• javadoc
• javap
• jdeps
• jlink
• jpackage
• jcmd
• jps
• jmap
• jstack
• jfr

1.3 Local Environment

• Project SDK configuration
• Compiler level configuration
• Language level configuration
• Run configuration
• Debug configuration
• Formatter
• Import optimization
• Code inspection

1.4 Build Tools

• Maven
• Project structure
• Dependency management
• Plugins
• Lifecycle
• Build profiles
• Multi-module project
• Maven/Gradle wrapper
• Local/remote repositories
• Maven BOM
• Dependency scope

1.5 Java Project Structure

• Package
• Source folder
• Test folder
• Resource folder
• Classpath
• Module path
• JAR
• Fat JAR
• Executable JAR
• Multi-release JAR

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2. Language Fundamentals

2.1 Basic Syntax

• Class
• Method
• main method
• Package declaration
• Import
• Statement
• Expression
• Block
• Comments
• Naming conventions
• Scope
• Variable lifetime

2.2 Primitive Types

• byte
• short
• int
• long
• float
• double
• char
• boolean
• Numeric literals
• Binary literal
• Underscores in numeric literals
• Overflow
• Underflow
• Implicit cast
• Explicit cast
• Numeric promotion
• Arithmetic operations

2.3 Wrapper Types

• Byte
• Short
• Integer
• Long
• Float
• Double
• Character
• Boolean
• Boxing
• Unboxing
• Autoboxing
• Wrapper cache
• == on wrappers
• .equals() on wrappers
• Null pointer with unboxing

2.4 Variables and Constants

• Local variables
• Instance fields
• Static fields
• Constants
• final
• static final
• Initialization
• Shadowing
• Local var
• Local type inference

2.5 Operators

• Arithmetic
• Assignment
• Comparison
• Logical
• Bitwise
• Shift
• Ternary
• Increment/decrement
• Operator precedence
• Short-circuit
• instanceof

2.6 Control Flow

• if
• else
• else if
• switch statement
• switch expression
• for
• Enhanced for
• while
• do while
• break
• continue
• return
• Labelled break
• Labelled continue

2.7 Arrays

• One-dimensional array
• Multidimensional array
• Array jagged
• Array initialization
• Index access
• ArrayIndexOutOfBoundsException
• Array of primitives
• Array of objects
• Array copy
• Arrays
• System.arraycopy

2.8 Strings

• String
• Immutability
• String pool
• Concatenation
• StringBuilder
• StringBuffer
• String.format
• formatted
• substring
• contains
• startsWith
• endsWith
• replace
• split
• join
• Text blocks
• Escape sequence
• Charset
• Unicode
• UTF-8

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3. Object-Oriented Programming

3.1 Classes and Objects

• Class
• Object
• Instance
• State
• Behavior
• Constructor
• Default constructor
• Constructor overloading
• Initializer block
• Static initializer block
• this
• Object references
• Mutability
• Object identity

3.2 Encapsulation

• Private fields
• Public methods
• Getter
• Setter
• Domain methods
• Invariants
• Constructor validation
• Defensive immutability
• Defensive copy
• Information hiding

3.3 Access Modifiers

• public
• private
• protected
• Package-private
• Visibility across packages
• Visibility in inheritance
• Public API
• Internal details
• Encapsulation boundary

3.4 Inheritance

• extends
• Superclass
• Subclass
• super
• Override
• Overload
• Polymorphism
• Dynamic dispatch
• Upcasting
• Downcasting
• final class
• final method
• Fragile base class problem
• Composition as an alternative

3.5 Abstract Classes

• abstract class
• Abstract method
• Concrete method
• Constructor in abstract class
• Template method
• Shared state
• Difference from interface

3.6 Interfaces

• interface
• Implementation
• Contract
• Abstract methods
• Default methods
• Static methods
• Private methods
• Constants in interfaces
• Multiple inheritance of type
• Functional interface
• Marker interface

3.7 Object

• toString
• equals
• hashCode
• getClass
• clone
• finalize
• equals contract
• hashCode contract
• Hash collision
• Objects as keys in HashMap
• Mutability and hash code

3.8 Nested Classes

• Static nested class
• Inner class
• Local class
• Anonymous class
• Access to outer context
• Coupling cost
• Use with listeners
• Use with builders

3.9 Enum

• enum
• Enum constants
• Fields in enums
• Constructors in enums
• Methods in enums
• Per-constant override
• values
• valueOf
• EnumSet
• EnumMap
• Enums as state machines

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4. Domain Modeling

4.1 Modeling Principles

• Entity
• Value object
• Aggregate
• Domain service
• Application service
• Repository
• Factory
• DTO
• Command
• Query
• Event
• Invariant
• Ubiquitous language

4.2 Immutability

• Immutable class
• final field
• Unmodifiable state
• Copy constructor
• Defensive copy
• Immutable collections
• Thread safety through immutability
• Value-based class
• Records as value carriers

4.3 Record

• record
• Record components
• Canonical constructor
• Compact constructor
• Record validation
• Methods in records
• Static fields in records
• Nested records
• Records as DTOs
• Records as value objects
• Limitations with JPA
• Limitations with reflection-based frameworks

4.4 Sealed Types

• sealed class
• sealed interface
• permits
• final
• non-sealed
• sealed + record
• Closed hierarchies
• Domain states
• Domain errors
• Exhaustiveness checking
• Algebraic modeling

4.5 Pattern Matching for the Domain

• Pattern matching with instanceof
• Pattern matching in switch
• Record patterns
• Guarded patterns
• Exhaustive switch
• Null handling in switch
• Sealed domain + switch
• Primitive patterns
• Deconstruction pattern

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5. Exception Handling

5.1 Fundamentals

• try
• catch
• finally
• throw
• throws
• Stack trace
• Exception propagation
• Checked exception
• Unchecked exception
• RuntimeException
• Error
• Throwable

5.2 Modern Handling

• Try-with-resources
• Multi-catch
• Rethrow
• Suppressed exception
• Exception wrapping
• Cause chain
• Custom exception
• Business exception
• Technical exception
• Validation exception
• Exception-to-response mapping

5.3 Strategies

• Fail fast
• Fail safe
• Recoverable errors
• Unrecoverable errors
• Exception logging
• Do not swallow exceptions
• Boundary exception handling
• Global exception handling
• Exception in async code
• Exception in stream pipeline

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6. Collections Framework

6.1 Main Interfaces

• Iterable
• Collection
• List
• Set
• SortedSet
• NavigableSet
• Queue
• Deque
• Map
• SortedMap
• NavigableMap
• Iterator
• ListIterator

6.2 List Implementations

• ArrayList
• LinkedList
• Vector
• Stack
• Random access
• Insertion
• Removal
• Iteration
• Big-O complexity
• Implementation choice

6.3 Set Implementations

• HashSet
• LinkedHashSet
• TreeSet
• EnumSet
• Uniqueness
• Natural ordering
• Custom ordering
• Hashing
• Collision
• Element mutability

6.4 Map Implementations

• HashMap
• LinkedHashMap
• TreeMap
• EnumMap
• WeakHashMap
• IdentityHashMap
• ConcurrentHashMap
• Keys
• Values
• Entry
• Hashing
• Ordering
• Null key
• Null value
• Key mutability

6.5 Queues and Deques

• ArrayDeque
• PriorityQueue
• BlockingQueue
• FIFO
• LIFO
• Priority ordering
• Producer/consumer
• Bounded queue
• Unbounded queue

6.6 Utility collections

• Collections
• Arrays
• Comparator
• Comparable
• Sorting
• Searching
• Shuffling
• Unmodifiable collections
• Immutable factory methods
• Synchronized wrappers
• Checked wrappers

6.7 Sequenced Collections

• SequencedCollection
• SequencedSet
• SequencedMap
• First element
• Last element
• Reverse view
• Ordered collection API
• Migration from legacy workarounds

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7. Generics and the Type System

7.1 Basic Generics

• Generic class
• Generic interface
• Generic method
• Type parameter
• Type argument
• Diamond operator
• Raw type
• Type safety
• Compile-time check
• Runtime type

7.2 Bounds

• Upper bound
• Multiple bound
• Recursive bound
• F-bounded polymorphism
• Method bounds
• Class bounds
• Bounds with interfaces

7.3 Wildcards

• Unbounded wildcard
• Upper bounded wildcard
• Lower bounded wildcard
• Capture conversion
• PECS
• Producer extends
• Consumer super
• API design with wildcards

7.4 Type erasure

• Erasure
• Bridge method
• Reifiable type
• Non-reifiable type
• Heap pollution
• Generic array creation
• Varargs generics
• @SafeVarargs
• Runtime limitations

7.5 Advanced Generics

• Generic builder
• Generic repository
• Generic mapper
• Type token
• Super type token
• Generic constraints
• Covariance
• Contravariance
• Invariance

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8. I/O, NIO, and File Systems

8.1 Classic I/O

• InputStream
• OutputStream
• Reader
• Writer
• BufferedInputStream
• BufferedOutputStream
• BufferedReader
• BufferedWriter
• FileInputStream
• FileOutputStream
• PrintWriter
• Encoding
• Buffering

8.2 NIO

• Path
• Files
• FileSystem
• FileSystems
• StandardOpenOption
• FileVisitOption
• FileVisitor
• SimpleFileVisitor
• Directory walking
• File attributes
• Symbolic link
• Temporary file
• Temporary directory

8.3 Channels and Buffers

• Channel
• FileChannel
• SocketChannel
• ServerSocketChannel
• ByteBuffer
• CharBuffer
• Direct buffer
• Heap buffer
• Selector
• Non-blocking I/O
• Memory-mapped file

8.4 File System Watch and Monitoring

• WatchService
• File create event
• File modify event
• File delete event
• Directory monitoring
• Overflow event
• Cross-platform behavior

8.5 Data Serialization

• Java serialization
• Serializable
• serialVersionUID
• transient
• Deserialization filtering
• JSON
• XML
• CSV
• Binary format
• Schema evolution

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9. Date, Time, Numbers, and Localization

9.1 Modern Date/Time

• LocalDate
• LocalTime
• LocalDateTime
• ZonedDateTime
• OffsetDateTime
• Instant
• Duration
• Period
• ZoneId
• ZoneOffset
• Clock
• DateTimeFormatter
• Date parsing
• Date formatting
• Timezone
• DST
• Technical timestamp
• Business date

9.2 Legacy Date/Time

• Date
• Calendar
• GregorianCalendar
• SimpleDateFormat
• Thread-safety legacy formatter
• Migration to java.time

9.3 Numbers

• BigDecimal
• BigInteger
• Precision
• Scale
• Rounding mode
• MathContext
• BigDecimal comparison
• equals vs compareTo
• Money calculation
• Percentages
• Rates
• Numeric overflow

9.4 Localization

• Locale
• Currency
• NumberFormat
• DecimalFormat
• MessageFormat
• ResourceBundle
• Pluralization
• Country-specific formats
• Currency formats
• Percentage formats

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10. Functional Java

10.1 Lambdas

• Lambda expression
• Lambda parameters
• Body expression
• Body block
• Variable capture
• Effectively final
• Target type
• Lambda vs anonymous class
• Lambdas and checked exceptions

10.2 Functional Interfaces

• @FunctionalInterface
• Predicate
• Function
• BiFunction
• Consumer
• BiConsumer
• Supplier
• UnaryOperator
• BinaryOperator
• Primitive functional interfaces
• Custom functional interface

10.3 Method References

• Static method reference
• Instance method reference
• Constructor reference
• Bound receiver
• Unbound receiver
• Overload ambiguity

10.4 Stream API

• Stream source
• Intermediate operation
• Terminal operation
• Lazy evaluation
• map
• flatMap
• filter
• peek
• sorted
• distinct
• limit
• skip
• takeWhile
• dropWhile
• reduce
• collect
• forEach
• findFirst
• findAny
• anyMatch
• allMatch
• noneMatch
• count
• Short-circuit operation
• Infinite stream

10.5 Collectors

• Collectors.toList
• Collectors.toSet
• Collectors.toMap
• Collectors.groupingBy
• Collectors.partitioningBy
• Collectors.mapping
• Collectors.flatMapping
• Collectors.filtering
• Collectors.reducing
• Collectors.joining
• Collectors.summarizingInt
• Custom collector
• Downstream collector
• Merge function
• Collector characteristics

10.6 Optional

• Optional
• OptionalInt
• OptionalLong
• OptionalDouble
• of
• ofNullable
• empty
• map
• flatMap
• filter
• orElse
• orElseGet
• orElseThrow
• ifPresent
• ifPresentOrElse
• Anti-pattern: Optional field
• Anti-pattern: Optional parameter
• Optional as return type

10.7 Practical Functional Programming

• Pure function
• Side effect
• Referential transparency
• Function composition
• Pipeline
• Declarative style
• Imperative style
• Immutability
• Parallel streams
• Stream limitations
• Stream pipeline debugging

10.8 Stream Gatherers

• Gatherer
• Stateful transformation
• Windowing
• Batching
• Sliding window
• Custom pipeline
• Gatherer lifecycle
• Parallel compatibility
• Practical use cases
• Alternatives with collectors

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11. Java Modules and Packaging

11.1 JPMS

• Module system
• module-info.java
• Named module
• Unnamed module
• Automatic module
• requires
• requires transitive
• exports
• opens
• opens to
• uses
• provides with
• Strong encapsulation
• Split package
• Module graph
• Readability
• Accessibility

11.2 Classpath vs module path

• Classpath
• Module path
• Migration from classpath
• Legacy dependencies
• Automatic module name
• Multi-release JAR
• ServiceLoader
• Reflection with modules
• Frameworks and modules

11.3 Runtime Images

• jlink
• Custom runtime image
• Required modules
• Runtime size reduction
• Startup
• Container image
• App distribution
• jpackage

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12. Classic Concurrency

12.1 Basic Threads

• Thread
• Runnable
• Thread lifecycle
• start
• run
• join
• sleep
• interrupt
• Daemon thread
• Thread priority
• Context class loader
• Thread naming

12.2 Memory model

• Java Memory Model
• Happens-before
• Visibility
• Atomicity
• Ordering
• Race condition
• Data race
• Safe publication
• Final field semantics
• Escape
• Thread-safe immutability

12.3 Synchronization

• synchronized
• Monitor
• Intrinsic lock
• Reentrant lock behavior
• volatile
• wait
• notify
• notifyAll
• Deadlock
• Livelock
• Starvation
• Lock contention
• Lock granularity

12.4 java.util.concurrent

• Executor
• ExecutorService
• ScheduledExecutorService
• Thread pool
• Future
• Callable
• CompletableFuture
• CompletionStage
• ForkJoinPool
• RecursiveTask
• RecursiveAction
• BlockingQueue
• ConcurrentHashMap
• CopyOnWriteArrayList
• CountDownLatch
• CyclicBarrier
• Semaphore
• Phaser
• Exchanger

12.5 Advanced Locks and Atomics

• Lock
• ReentrantLock
• ReadWriteLock
• StampedLock
• Condition
• AtomicInteger
• AtomicLong
• AtomicReference
• LongAdder
• LongAccumulator
• CAS
• ABA problem
• False sharing

12.6 Async programming

• CompletableFuture.supplyAsync
• thenApply
• thenCompose
• thenCombine
• allOf
• anyOf
• exceptionally
• handle
• whenComplete
• Timeout
• Cancellation
• Custom executor
• Error propagation
• Composition vs nesting

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13. Modern Concurrency: Project Loom

13.1 Virtual threads

• Platform thread
• Virtual thread
• Carrier thread
• Scheduler
• Blocking I/O
• Mount
• Unmount
• Pinning
• Thread-per-request
• Executors.newVirtualThreadPerTaskExecutor
• Thread.ofVirtual
• Debug virtual threads
• Thread dumps with virtual threads
• CPU-bound limitations
• Limitations with native locks

13.2 Structured Concurrency

• Structured task scope
• Task group
• Parent-child lifecycle
• Fork
• Join
• Shutdown
• Cancellation
• Failure propagation
• Result aggregation
• Timeout
• Concurrency as a structured unit
• Structured error handling

13.3 Scoped Values

• Scoped value
• Immutable context
• Controlled propagation
• Alternative to ThreadLocal
• Use with virtual threads
• Bound scope
• Nested scope
• Request context
• Security context
• Tracing context

13.4 Enterprise Migration

• Virtual threads in web services
• Virtual threads with JDBC
• Virtual threads with HTTP client
• Virtual threads with Spring Boot
• ThreadLocal legacy
• Pool sizing
• Connection pool
• Backpressure
• Rate limiting
• Observability
• Load test

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14. Networking and HTTP

14.1 Networking Basics

• Socket
• ServerSocket
• TCP
• UDP
• DNS
• Timeout
• Connection refused
• Connection reset
• Keep-alive
• TLS
• Proxy
• Firewall

14.2 HTTP Client

• HttpClient
• HttpRequest
• HttpResponse
• HTTP/1.1
• HTTP/2
• HTTP/3
• Synchronous send
• Asynchronous send
• BodyPublisher
• BodyHandler
• Headers
• Timeout
• Redirect
• Authentication
• CookieHandler
• SSLContext
• Connection reuse
• Error handling

14.3 Client Resilience

• Retry
• Exponential backoff
• Timeout budget
• Circuit breaker
• Bulkhead
• Rate limiter
• Idempotency
• Correlation ID
• Request tracing
• Metrics
• Logging request/response
• Sensitive data redaction

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15. Security and Cryptography

15.1 Security Fundamentals

• Secure coding
• Input validation
• Output encoding
• Secrets management
• Password hashing
• TLS
• Certificate chain
• Trust model
• Keystore
• Truststore
• JCA
• JCE

15.2 Crypto API

• SecureRandom
• Hash
• HMAC
• Symmetric encryption
• Asymmetric encryption
• Signature
• KeyPair
• KeyGenerator
• KeyFactory
• Cipher
• MessageDigest
• Mac
• Signature API
• KEM API
• KDF API
• PEM API
• ML-KEM
• ML-DSA

15.3 Serialization security

• Java serialization risks
• Deserialization attack
• Serialization filtering
• ObjectInputFilter
• Allow-list
• Deny-list
• Alternative JSON
• Alternative protobuf
• Alternative Avro
• Backward compatibility

15.4 Platform security evolution

• Security Manager
• Security Manager deprecation
• Security Manager disabling
• Removal of legacy APIs
• Strong encapsulation
• Restrictions on final field reflection
• Deprecation of Unsafe
• Migration from internal JDK APIs

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16. Reflection, Annotations, and Metaprogramming

16.1 Reflection

• Class
• Field
• Method
• Constructor
• getDeclaredFields
• getDeclaredMethods
• setAccessible
• Private access
• Reflection performance
• Reflection and modules
• Reflection and final
• Reflection and frameworks
• Reflection and security

16.2 Annotations

• Custom annotations
• @Target
• @Retention
• @Inherited
• @Repeatable
• Runtime annotation
• Source annotation
• Class annotation
• Annotations on type use
• Annotation processing
• Compile-time code generation

16.3 Dynamic proxy

• Proxy
• InvocationHandler
• Interface proxy
• AOP
• Logging proxy
• Transaction proxy
• JDK proxy limitations
• Proxy vs bytecode generation

16.4 MethodHandles and VarHandles

• MethodHandle
• MethodHandles.Lookup
• invoke
• invokeExact
• CallSite
• VarHandle
• Field access
• Array access
• Memory ordering
• Reflection replacement
• Performance

16.5 Class-File API

• Class file structure
• Constant pool
• Method descriptor
• Field descriptor
• Attribute
• Bytecode instruction
• Class file parsing
• Class file generation
• Class file transformation
• Tooling
• Framework integration

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17. JVM internals

17.1 JVM Architecture

• Bytecode
• Class file
• Class loader
• Bootstrap class loader
• Platform class loader
• Application class loader
• Custom class loader
• Linking
• Verification
• Preparation
• Resolution
• Initialization
• Runtime data areas

17.2 Memory

• Heap
• Stack
• Metaspace
• Code cache
• Native memory
• Thread stack
• Eden
• Survivor
• Old generation
• TLAB
• Object header
• Compressed OOPs
• Compact object headers
• Escape analysis
• Scalar replacement

17.3 JIT and Optimization

• Interpreter
• C1 compiler
• C2 compiler
• Tiered compilation
• Runtime profiling
• Inlining
• Deoptimization
• Loop optimization
• Lock elimination
• Dead code elimination
• Intrinsics
• Warmup
• Benchmark pitfalls

17.4 Class Loading and Startup

• Class loading cost
• CDS
• AppCDS
• Dynamic CDS
• AOT class loading
• AOT linking
• AOT object caching
• Lazy constants
• Startup profiling
• Startup optimization
• Container startup

17.5 Runtime Observability

• Thread dump
• Heap dump
• GC log
• JFR
• JMX
• MBeans
• Native memory tracking
• Safepoint logging
• Allocation profiling
• Lock profiling
• CPU profiling

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18. Garbage Collection and Performance

18.1 GC Fundamentals

• Allocation
• Reachability
• Root set
• Young generation
• Old generation
• Minor GC
• Major GC
• Full GC
• Stop-the-world
• Concurrent phase
• Parallel phase
• Compaction
• Fragmentation
• Promotion
• Allocation rate

18.2 Garbage collector

• Serial GC
• Parallel GC
• G1 GC
• ZGC
• Generational ZGC
• Shenandoah GC
• Epsilon GC
• GC selection
• Throughput goal
• Latency goal
• Memory footprint goal
• Pause time goal

18.3 GC tuning

• Heap sizing
• -Xms
• -Xmx
• GC logging
• G1 region size
• Pause target
• String deduplication
• Humongous allocation
• ZGC configuration
• Container memory limit
• CPU limit
• Native memory
• Memory leak analysis

18.4 Performance engineering

• JMH
• Warmup
• Measurement iteration
• Fork
• Blackhole
• Dead-code elimination
• Escape analysis impact
• Allocation benchmark
• CPU-bound benchmark
• I/O-bound benchmark
• Profiling
• Regression benchmark

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19. Foreign Function, Memory, and Native Interop

19.1 JNI

• JNI basics
• Native method
• Header generation
• Native library loading
• Marshaling
• Crash risk
• Memory safety
• Performance overhead
• Legacy use cases

19.2 Foreign Function & Memory API

• MemorySegment
• Arena
• Linker
• SymbolLookup
• FunctionDescriptor
• ValueLayout
• Native call
• Off-heap memory
• Bounds checking
• Lifetime management
• Segment scope
• Native interop
• Replacement for JNI in common cases

19.3 Off-Heap and Performance

• Direct memory
• Off-heap allocation
• Memory layout
• Native buffer
• Zero-copy
• Memory mapping
• Resource cleanup
• Cleaner
• Native memory tracking

---

20. Vector API and High-Performance Computing

20.1 SIMD

• SIMD
• Scalar operation
• Vector operation
• CPU vector register
• Lane
• Species
• Portability
• Fallback
• Auto-vectorization
• Manual vectorization

20.2 Vector API

• Vector species
• Vector mask
• Load
• Store
• Arithmetic operation
• Reduction
• Comparison
• Blend
• Performance benchmark
• Incubator module
• Numeric use cases
• AI/ML use cases
• Crypto use cases
• Image processing use cases

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21. Testing

21.1 Unit testing

• JUnit 5
• Test lifecycle
• Assertions
• Parameterized tests
• Nested tests
• Test naming
• Test fixture
• Test isolation
• Boundary tests
• Negative tests
• Exception tests

21.2 Mocking

• Mockito
• Mock
• Stub
• Spy
• ArgumentCaptor
• Verification
• Strict stubbing
• Mocking final classes
• Mocking static methods
• Test double
• Fake
• In-memory implementation

21.3 Integration testing

• Integration test
• Testcontainers
• Database container
• Kafka container
• WireMock
• MockWebServer
• HTTP contract test
• Database migration test
• Transactional test
• Environment isolation

21.4 Quality gates

• JaCoCo
• Coverage line
• Coverage branch
• Mutation testing
• PIT
• Static analysis
• Checkstyle
• SpotBugs
• PMD
• Error Prone
• SonarQube

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22. Logging, Monitoring, and Observability

22.1 Logging

• java.util.logging
• SLF4J
• Logback
• Log4j2
• Log level
• Structured logging
• MDC
• Correlation ID
• Sensitive data redaction
• Async logging
• Log rotation

22.2 Metrics

• Counter
• Gauge
• Timer
• Histogram
• Percentile
• Throughput
• Latency
• Error rate
• Saturation
• JVM metrics
• GC metrics
• Thread metrics

22.3 Tracing

• Distributed tracing
• Span
• Trace ID
• Parent span
• Context propagation
• OpenTelemetry
• Sampling
• Baggage
• Error trace
• Performance trace

22.4 JVM diagnostics

• JFR
• JMC
• VisualVM
• JConsole
• Async Profiler
• Flame graph
• CPU profiling
• Allocation profiling
• Lock profiling
• Safepoint profiling

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23. Enterprise Java and Microservices

23.1 JDBC and Databases

• JDBC
• Driver
• Connection
• PreparedStatement
• ResultSet
• Transaction
• Isolation level
• Connection pool
• Batch insert
• SQL injection prevention
• Manual mapping
• Schema migration

23.2 Spring Boot

• Dependency injection
• Bean lifecycle
• Configuration properties
• REST controller
• Service layer
• Repository layer
• Validation
• Exception handler
• Actuator
• Profiles
• Testing Spring
• Virtual threads in Spring
• Observability Spring

23.3 Persistence

• JPA
• Hibernate
• Entity
• Value object
• Repository
• Lazy loading
• Eager loading
• N+1 query
• Transaction boundary
• Dirty checking
• Optimistic locking
• Pessimistic locking
• Projection
• DTO mapping

23.4 Microservices

• REST API
• OpenAPI
• JSON serialization
• Validation
• Idempotency
• Retry
• Circuit breaker
• Rate limiting
• API versioning
• Distributed tracing
• Health check
• Readiness
• Liveness
• Graceful shutdown

23.5 Messaging

• Queue
• Topic
• Producer
• Consumer
• Consumer group
• Offset
• Acknowledgement
• Retry topic
• Dead letter queue
• Ordering
• Idempotent consumer
• Exactly-once semantics
• At-least-once semantics
• Backpressure

23.6 Containers and Cloud

• Dockerfile for Java
• Layered JAR
• JVM in container
• Memory limits
• CPU limits
• Startup time
• Image size
• Distroless image
• Alpine caveats
• Kubernetes deployment
• ConfigMap
• Secret
• Horizontal scaling
• Resource request
• Resource limit

---

24. Java Evolution by Version

24.1 Java 1.0

• Classes
• Objects
• Interfaces
• Package
• Exception
• Thread
• Applet
• AWT
• Basic I/O
• JVM
• Bytecode

24.2 Java 1.1

• Inner classes
• Reflection
• JDBC
• RMI
• JavaBeans
• Object serialization
• Event model
• Internationalization

24.3 Java 1.2

• Collections Framework
• Swing
• Java 2 platform
• strictfp
• JIT improvements
• Security policy
• Accessibility API

24.4 Java 1.3

• HotSpot JVM
• JNDI
• Dynamic proxy
• Java Sound
• RMI over IIOP
• Performance VM improvements

24.5 Java 1.4

• assert
• Regular expressions
• NIO
• Logging API
• Preferences API
• XML processing
• XSLT
• Exception chaining
• IPv6 support

24.6 Java 5

• Generics
• Enhanced for
• Autoboxing/unboxing
• Enum
• Annotations
• Varargs
• Static import
• java.util.concurrent
• Formatter
• Scanner
• Instrumentation API
• Metadata

24.7 Java 6

• Scripting API
• Compiler API
• Annotation processing
• JDBC 4.0
• Web services APIs
• Monitoring improvements
• Management improvements
• Desktop API
• Performance improvements

24.8 Java 7

• String in switch
• Try-with-resources
• Diamond operator
• Multi-catch
• Precise rethrow
• Binary literals
• Underscore in numeric literals
• Fork/Join Framework
• NIO.2
• Path
• Files
• WatchService
• invokedynamic

24.9 Java 8

• Lambda expressions
• Method references
• Functional interfaces
• Stream API
• Default methods
• Static methods in interfaces
• Optional
• java.time
• CompletableFuture
• Nashorn JavaScript engine
• Repeating annotations
• Type annotations
• Base64 API
• Parallel array sorting
• Compact profiles

24.10 Java 9

• Java Platform Module System
• module-info.java
• JShell
• Collection factory methods
• Private interface methods
• Multi-release JAR
• Process API improvements
• Stack-Walking API
• VarHandles
• Compact Strings
• G1 default GC
• Unified JVM logging
• HTTP/2 Client incubator
• Reactive Streams Flow API
• DRBG SecureRandom
• Serialization filtering
• jlink
• Runtime images

24.11 Java 10

• Local-variable type inference var
• Time-based release versioning
• Application Class-Data Sharing
• Parallel Full GC for G1
• Garbage-Collector Interface
• Thread-local handshakes
• Heap allocation on alternative memory devices
• Root certificates
• Experimental Java-Based JIT Compiler

24.12 Java 11

• HTTP Client standard
• Single-file source-code launcher
• var in lambda parameters
• Flight Recorder
• Epsilon GC
• ZGC experimental
• TLS 1.3
• ChaCha20 and Poly1305
• Unicode 10
• Dynamic class-file constants
• Nest-based access control
• Removal of Java EE modules
• Removal of CORBA modules
• Deprecation of Nashorn
• Deprecation of Pack200

24.13 Java 12

• Switch expressions preview
• JVM Constants API
• Shenandoah experimental
• Abortable mixed collections for G1
• Promptly return unused committed memory from G1
• Default CDS archives
• Microbenchmark suite
• One AArch64 port

24.14 Java 13

• Text Blocks preview
• Switch expressions second preview
• Dynamic CDS archives
• ZGC uncommit unused memory
• Reimplementation of legacy Socket API
• FileSystems new file system methods

24.15 Java 14

• Switch expressions standard
• Records preview
• Pattern matching for instanceof preview
• Helpful NullPointerExceptions
• JFR Event Streaming
• Packaging tool incubator
• NUMA-aware memory allocation for G1
• Non-volatile mapped byte buffers
• Removal of CMS GC
• Removal of Pack200
• ZGC on macOS
• ZGC on Windows

24.16 Java 15

• Text Blocks standard
• Sealed Classes preview
• Hidden Classes
• ZGC production
• Shenandoah production
• Records second preview
• Pattern matching for instanceof second preview
• Foreign-Memory Access API second incubator
• EdDSA
• Reimplementation of DatagramSocket API
• Disable biased locking
• Removal of Nashorn
• Removal of rmic

24.17 Java 16

• Records standard
• Pattern matching for instanceof standard
• jpackage standard
• Vector API incubator
• Foreign Linker API incubator
• Foreign-Memory Access API third incubator
• Unix-domain socket channels
• Elastic Metaspace
• Strong encapsulation by default
• Warnings for value-based classes
• Alpine Linux port
• Windows/AArch64 port

24.18 Java 17

• Sealed Classes standard
• Pattern matching for switch preview
• Strongly encapsulate JDK internals
• Context-specific deserialization filters
• Enhanced pseudo-random number generators
• Foreign Function & Memory API incubator
• Vector API second incubator
• Deprecate Security Manager for removal
• Removal of RMI Activation
• Removal of experimental AOT and JIT compiler
• macOS/AArch64 port

24.19 Java 18

• UTF-8 by default
• Simple Web Server
• Code snippets in Java API documentation
• Core reflection reimplemented with MethodHandles
• Internet-Address Resolution SPI
• Pattern matching for switch second preview
• Vector API third incubator
• Foreign Function & Memory API second incubator
• Deprecate finalization for removal

24.20 Java 19

• Virtual Threads preview
• Structured Concurrency incubator
• Record Patterns preview
• Pattern matching for switch third preview
• Foreign Function & Memory API preview
• Vector API fourth incubator
• Linux/RISC-V port

24.21 Java 20

• Virtual Threads second preview
• Scoped Values incubator
• Structured Concurrency second incubator
• Record Patterns second preview
• Pattern matching for switch fourth preview
• Foreign Function & Memory API second preview
• Vector API fifth incubator

24.22 Java 21

• Virtual Threads standard
• Sequenced Collections
• Record Patterns standard
• Pattern Matching for switch standard
• Generational ZGC
• String Templates preview
• Unnamed Patterns and Variables preview
• Unnamed Classes and Instance Main Methods preview
• Scoped Values preview
• Structured Concurrency preview
• Key Encapsulation Mechanism API
• Foreign Function & Memory API third preview
• Vector API sixth incubator

24.23 Java 22

• Foreign Function & Memory API standard
• Unnamed Variables and Patterns standard
• Launch multi-file source-code programs
• Class-File API preview
• Stream Gatherers preview
• Structured Concurrency second preview
• Scoped Values second preview
• Statements before super(...) preview
• Vector API seventh incubator
• Region pinning for G1

24.24 Java 23

• Markdown documentation comments
• Primitive types in patterns preview
• Class-File API second preview
• Stream Gatherers second preview
• Module Import Declarations preview
• Structured Concurrency third preview
• Scoped Values third preview
• Flexible Constructor Bodies second preview
• Vector API eighth incubator
• ZGC generational mode by default
• Deprecate memory-access methods in Unsafe for removal

24.25 Java 24

• Stream Gatherers standard
• Class-File API standard
• Synchronize Virtual Threads without Pinning
• AOT Class Loading and Linking
• Compact Object Headers experimental
• KDF API preview
• ML-KEM
• ML-DSA
• Scoped Values fourth preview
• Structured Concurrency fourth preview
• Simple Source Files and Instance Main Methods fourth preview
• Module Import Declarations second preview
• Flexible Constructor Bodies third preview
• Primitive Types in Patterns second preview
• Vector API ninth incubator
• Warn upon use of memory-access methods in Unsafe
• Security Manager disabled
• Remove non-generational ZGC mode

24.26 Java 25

• Scoped Values standard
• Compact Source Files and Instance Main Methods standard
• Module Import Declarations standard
• Flexible Constructor Bodies standard
• Stable Values preview
• Compact Object Headers
• JFR Cooperative Sampling
• Structured Concurrency fifth preview
• Primitive Types in Patterns third preview
• Vector API tenth incubator
• Ahead-of-Time Method Profiling
• Key Derivation Function API

24.27 Java 26

• JEP 500 - Prepare to Make Final Mean Final
• JEP 504 - Remove the Applet API
• JEP 516 - Ahead-of-Time Object Caching with Any GC
• JEP 517 - HTTP/3 for the HTTP Client
• JEP 522 - G1 GC: Improve Throughput by Reducing Synchronization
• JEP 524 - PEM Encodings of Cryptographic Objects
• JEP 525 - Structured Concurrency
• JEP 526 - Lazy Constants
• JEP 529 - Vector API
• JEP 530 - Primitive Types in Patterns, instanceof, and switch

---

25. Progressive Study Path

25.1 Phase 1 - Basic Java

• Setup JDK
• Basic syntax
• Primitive types
• Strings
• Array
• Control flow
• Classes
• Objects
• Methods
• Package
• Access modifier
• Basic exceptions

25.2 Phase 2 - Java Core

• Advanced OOP
• Collections
• Generics
• Advanced exception handling
• I/O
• NIO
• Date/time
• BigDecimal
• Enum
• Immutability
• Basic testing

25.3 Phase 3 - Java 8

• Lambda
• Functional interface
• Method reference
• Stream API
• Optional
• Collector
• Basic CompletableFuture
• Default methods
• java.time

25.4 Phase 4 - Java 9-17

• Module system
• JShell
• Collection factory methods
• var
• HTTP Client
• Text Blocks
• Switch expressions
• Records
• Pattern matching instanceof
• Sealed classes
• JFR
• Strong encapsulation

25.5 Phase 5 - Java 18-21

• UTF-8 by default
• Simple Web Server
• Virtual Threads
• Sequenced Collections
• Record Patterns
• Pattern Matching for switch
• Generational ZGC
• Scoped Values preview
• Structured Concurrency preview
• KEM API

25.6 Phase 6 - Java 22-26

• Foreign Function & Memory API
• Class-File API
• Stream Gatherers
• Scoped Values
• Structured Concurrency
• Compact Source Files
• Instance Main Methods
• Module Import Declarations
• Flexible Constructor Bodies
• Stable Values
• Compact Object Headers
• AOT Class Loading
• AOT Object Caching
• HTTP/3
• PEM API
• Lazy Constants
• Vector API
• Primitive Types in Patterns
• Final field restrictions

25.7 Phase 7 - JVM and Performance

• Bytecode
• Class loading
• JIT
• Heap
• Stack
• Metaspace
• GC
• GC logs
• JFR
• Profiling
• Benchmarking
• Thread dump
• Heap dump
• Memory leak analysis

25.8 Phase 8 - Enterprise Java

• Advanced Maven/Gradle
• JDBC
• Spring Boot
• JPA/Hibernate
• REST API
• Microservices
• Messaging
• Integration testing
• Observability
• Docker
• Kubernetes
• Performance in containers