Java – Updates, How-Tos, and Tutorials

Latest Articles

JEP 500: Final Means Final – Deep Reflection in Java 26

October 20, 2026A harmless dependency overwrites a final field via deep reflection. What JEP 500 does about it from Java 26 on – and what you should do.

Java BufferedReader: readLine(), lines(), and Reading Line by Line

October 17, 2026Java BufferedReader explained: read files line by line with readLine() and lines(), character encoding, console input, performance, Scanner.

Serialization in Java: Serializable, transient, serialVersionUID

October 15, 2026Java serialization explained: Serializable, ObjectOutputStream, transient, serialVersionUID, records, and deserialization filters.

Java Stream Group By with Collectors.groupingBy()

October 12, 2026Java stream group by with Collectors.groupingBy(): grouping by a key, counting, averaging, downstream collectors, partitioningBy().

Java Basics + Data Structures

This category covers core Java functionality, such as String processing, object conversion, and random number generation, as well as data structures, such as collections, maps and sets, trees, queues, deques, and stacks.

How to Declare and Initialize Arrays in Java

How to declare and initialize arrays in Java, fill and copy them, and convert lists, sets, and streams into arrays – including 2D arrays.

Java Array Length and Size: .length, 2D Arrays, Max Array Size

How to get and set the length of a Java array, including 2D arrays – plus an array’s memory use in Java 27 and the maximum array size.

Java main() Method – Syntax and Simplification Since Java 25

What does public static void main(String[] args) mean? The main() method, step by step – and why void main() is enough since Java 25.

Generating Random Numbers in Java – and Predicting Them

Random numbers in Java: Math.random(), Random, ThreadLocalRandom, and SecureRandom – and why pseudorandom numbers can be predicted.

compareTo, Comparable, Comparator – Comparing Objects in Java

How to compare objects in Java: Comparable and compareTo() define the natural order, Comparator.comparing() any other – with examples.

Java substring() Method: How to Use It and How It Works

Java substring() with examples – from an index, to the end, from the end – and how the method works internally, from Java 1 to today.

Java Streams + Functional Programming

This category covers the Stream API and the language features it builds on: lambda expressions, functional interfaces, and Optional. It also covers individual stream operations such as reduce() and Collectors.toMap(), and stream gatherers for writing your own operations.

Java Streams (with Examples)

Java Streams explained from the ground up: how a pipeline works, every operation with an example, lazy evaluation, and the mistakes to avoid.

Java Lambda Expressions (with Examples)

Java lambda expressions explained from the ground up: syntax, target types, effectively final, method references, and how the JVM runs them.

Java Optional (with Examples)

Java Optional explained with examples: of() and ofNullable(), orElse() vs. orElseGet(), map() and flatMap(), when to use Optional, and what Valhalla changes.

Java Functional Interfaces (with Examples)

Java functional interfaces explained from the ground up: the rule, @FunctionalInterface, all 43 interfaces in java.util.function, and when to write your own.

Java Stream reduce() (with Examples)

Java Stream reduce() explained: the three variants, identity and combiner, parallel streams, and when to use collect() instead.

Java Collectors.toMap() (with Examples)

Java Collectors.toMap() explained: collecting a stream into a map, resolving duplicate keys with a merge function, map type, null values.

Java Stream Group By with Collectors.groupingBy()

Java stream group by with Collectors.groupingBy(): grouping by a key, counting, averaging, downstream collectors, partitioningBy().

Java Parallel Streams (with Examples)

Java parallel streams explained: how the ForkJoinPool splits the work, measured limits of parallel(), and the rules for correct results.

Java Stream Gatherers – Write Your Own Stream Operations!

Stream Gatherers (JEP 485): the five built-in gatherers from windowFixed to mapConcurrent – and how to write your own stream operations.

Java versions cheat sheet – stacked PDF pages

Free PDF:

Your Java Versions Cheat Sheet

All features from Java 10 to Java 27 – one page per version

Get the compact overview of all Java versions. You’ll instantly know which updates are worth adopting in your project – and see at a glance which Java version introduced a specific feature.

You get access to this PDF collection by signing up for my newsletter. You can opt-out at any time.

Project Amber – Java Syntax Enhancements

In Project Amber, new Java language features are being developed such as switch expressions, text blocks, records, pattern matching, and sealed classes.

Java Switch Expressions (JEP 361): Arrows, yield, No break

Switch expressions since Java 14 (JEP 361): arrow cases without break, values via yield, exhaustiveness for enums – and what Java 21 added.

Java Text Blocks: Multiline Strings with Triple Quotes (JEP 378)

Text blocks: multiline strings in Java without \n. How to write and indent them, and which two new escape sequences you get.

Java Records: The Complete Guide (with Examples)

What are Java records? Why do we need them? How do you implement and use them? And what about inheritance, reflection, and serialization?

Sealed Classes and Interfaces in Java

Sealed classes and interfaces in Java: sealed, permits, and non-sealed – and how the compiler uses them to check switch exhaustiveness.

Unnamed Variables & Patterns in Java (JEP 456)

Since Java 22, you mark unused variables and patterns with the underscore (_): in catch blocks, lambdas, loops, switch. With all the rules.

String Templates in Java: What Happened to String Interpolation

Java string templates (Java 21/22) were withdrawn: how interpolation with STR and FMT worked, why the design was pulled, what to use now.

Flexible Constructor Bodies (JEP 513): Code Before super() in Java 25

Flexible Constructor Bodies (JEP 513): since Java 25, code can run before super(...) and this(...). Examples, restrictions, compiler errors.

Java Imports: Classes, Packages, and Entire Modules (JEP 511)

Java imports from class to module: packages, static imports, java.lang – and import module, which imports entire modules since Java 25.

Primitive Types in Patterns, instanceof, and switch (Java)

Primitive type patterns bring int, long, and double into pattern matching. Use them in instanceof and switch – a preview since Java 23.

Withers in Java: Derived Record Creation Expressions (JEP 468)

Withers (JEP 468) derive new Java records by specifying only the changed components – no wither methods, no boilerplate.

Advanced Java Topics

This section covers advanced Java topics such as reflection, concurrency, garbage collection, and the Java memory model.

Java Virtual Threads (JEP 444): How They Work, Examples, Pitfalls

Virtual threads in Java (Project Loom): how they work and how to handle millions of blocking tasks without async code – with examples.

Lazy Constants in Java (Stable Values) – Safe and Lazy Initialization

Lazy Constants in Java (formerly Stable Values) explained: initialize values thread-safely on first use – plus Lazy Lists, Sets, and Maps.

Structured Concurrency in Java 27 with StructuredTaskScope

Structured Concurrency in Java 27: how StructuredTaskScope forks subtasks, cancels them, and propagates errors – with a custom joiner.

Double-Checked Locking in Java: Why You Need volatile

Double-Checked Locking in Java: why the original idiom is broken, why volatile fixes it – and when Lazy Constants are the better choice.

Java Scoped Values (JEP 506) Explained – vs. ThreadLocal

Scoped Values (JEP 506) replace ThreadLocal since Java 25: binding, rebinding, child-thread inheritance – and where ThreadLocal falls short.

Initialization-on-Demand Holder Idiom in Java (Holder Pattern)

Thread-safe lazy initialization of static fields without synchronization: how the Initialization-on-Demand Holder Idiom works in Java.

Java FFM API (JEP 454): Foreign Function & Memory API Tutorial

Learn how to use the FFM API (Project Panama) to call native libraries from Java and access native memory – without JNI.

Java Object Headers and Compressed Class Pointers

Java object header layout: Mark Word, Class Word, Compressed Class Space, and Compressed Class Pointers – and how big the header is.

Compressed Oops in Java: 32-Bit References and the 32 GB Limit

Compressed Oops: 32-bit references on 64-bit systems, heaps below 32 GB, the JVM’s four modes – and when disabling them pays off.

Compact Object Headers in Java (JEP 519) – default since Java 27

How Java shrinks object headers from 96 to 64 bits without losing information. Compact Object Headers (JEP 519), default since Java 27.

Ahead-of-Time Class Loading & Linking: Java’s AOT Cache

Ahead-of-Time Class Loading & Linking speeds up Java application startup by up to 42%. Here’s how to create the AOT cache, step by step.

Java ByteBuffer Explained: position, limit, flip(), compact()

Java’s ByteBuffer step by step: position, limit, and capacity, put() and get(), flip() and compact() – with a diagram for every step.

Java Deep Reflection: How to Hack Integer and String

Can 2 + 3 = 6 in Java? How deep reflection changes cached Integers and Strings – and what Java 16 and 26 require to still allow it.

JEP 500: Final Means Final – Deep Reflection in Java 26

A harmless dependency overwrites a final field via deep reflection. What JEP 500 does about it from Java 26 on – and what you should do.

New Java Features

Every new Java release brings big and small changes:

Changes to the language itself (lambdas, the module system, var, improvements from Project Amber, ...),
API enhancements and
Performance improvements under the hood.

In addition, legacy features are regularly marked as “deprecated”, then as “deprecated for removal”, and later completely removed from the JDK.

In this series of articles, you will learn everything about the most important changes in each Java release.

Java 9 Features (with Examples)

All Java 9 features with examples: module system, jshell, List.of(), private interface methods, Flow API, Stack-Walking API, Process API, and more.

Java 10 Features (with Examples)

All new features of Java 10 with examples: “var”, Immutable Collections, Optional.orElseThrow(), Application Class-Data Sharing, and more.

Java 11 Features (with Examples)

Java 11 with examples: “var” in lambdas, HttpClient, new String and Files methods, single-file programs, Flight Recorder, and more.

Java 12 Features (with Examples)

All Java 12 features with examples: String.indent() and transform(), Files.mismatch(), Teeing Collector, Compact Number Format, Default CDS.

Java 13 Features (with Examples)

All new features of Java 13 with examples: Switch Expressions with yield, Text Blocks, Dynamic CDS Archives, Soft Max Heap Size, and more.

Java 14 Features (with Examples)

All Java 14 features with examples: Switch Expressions (JEP 361), Helpful NullPointerExceptions, Records and Pattern Matching in preview.

Java 15 Features (with Examples)

All Java 15 features with examples: text blocks, String.formatted(), ZGC and Shenandoah production-ready, sealed classes in preview.

Java 16 Features (with Examples)

Java 16 Features with examples: Records, “Pattern Matching for instanceof”, Stream.toList(), jpackage, Strong Encapsulation, and more.

Java 17 Features (with Examples)

Java 17 features (LTS) with examples: Sealed Classes, InstantSource, HexFormat, context-specific deserialization filters, and more.

Java 18 Features (with Examples)

Java 18 features with examples: UTF-8 by default, jwebserver, the @snippet tag in JavaDoc, Internet-Address Resolution SPI, and more.

Java 19 Features: Virtual Threads, Record Patterns and More

The new Java 19 features with examples: Virtual Threads (preview), Record Patterns (preview), Foreign Function & Memory API (preview) + more

Java 20 Features (with Examples)

Java 20 features with examples: Scoped Values, Record Patterns, Pattern Matching for switch, Virtual Threads – and what became of them.

Java 21 Features (with Examples)

All Java 21 features with examples: virtual threads, sequenced collections, record patterns, pattern matching for switch, and more.

Java 22 Features (with Examples)

Java 22 features with examples: Foreign Function & Memory API, unnamed variables & patterns, multi-file programs, Stream Gatherers + more.

Java 23 Features (with Examples)

All Java 23 features with examples: Markdown in JavaDoc, import modules, primitive type patterns, set fields before super() + more!

Java 24 Features (with Examples)

Java 24 with code examples: Stream Gatherers, synchronized in virtual threads without pinning, AOT Class Loading, Compact Object Headers.

Java 25 Features (with Examples)

Java 25 (LTS): Scoped Values, Compact Source Files, Flexible Constructor Bodies, Compact Object Headers, and more – explained with examples.

Java 26 Features (with Examples)

Java 26 features (March 2026) with examples: HTTP/3, Lazy Constants, AOT caching with any GC, “final means final”, a faster G1, and more.

Java 27 Features (with Examples)

Java 27 explained – with code examples: Compact Object Headers by default, G1 everywhere, quantum-safe TLS, Lazy Sets and more.

How to Change Java Versions in Windows (updated for Java 28)

How to install multiple Java versions on Windows in parallel? How to change Java versions on the command line? (Up to JDK 28)

Java Modernization: How to Get Your Team and Management on Board

How to get your team and management excited about Java modernization – with clear arguments, practical examples & quick wins for sustainable success.

Article Series “Files in Java”

What you’ll learn:

How to read and write text and binary files
Character encoding and line breaks
Constructing relative and absolute file and directory names with File, Path, and Paths
How to list all files of a directory, how to search files
How to move, rename, copy and delete files
Saving complex objects and primitive data types in binary files
Writing and reading files with FileChannel and ByteBuffer

How to Read a File in Java – to String, Byte Array, or Line by Line

Read a file in Java – into a string, a byte array, or line by line: Files, FileReader and BufferedReader compared, plus character encoding.

Java BufferedReader: readLine(), lines(), and Reading Line by Line

Java BufferedReader explained: read files line by line with readLine() and lines(), character encoding, console input, performance, Scanner.

Java Write to File: Files.writeString(), FileWriter, BufferedWriter

How to write a string, lines, or a byte array to a file in Java: Files, FileWriter, BufferedWriter – and when buffering pays off.

File and Directory Names in Java: File, Path, Paths

Filename, directory name, path – what’s the difference? How to build file paths in Java with File, Path, and Paths, independent of the OS.

How to Copy, Move, and Delete Files and Directories (Java Files Tutorial)

How to list directories and copy, move, rename and delete files and whole directory trees in Java – with the NIO.2 Files API.

Java DataOutputStream and DataInputStream (with Examples)

How to write primitive data types and strings to binary files and read them back – with DataOutputStream and DataInputStream.

Serialization in Java: Serializable, transient, serialVersionUID

Java serialization explained: Serializable, ObjectOutputStream, transient, serialVersionUID, records, and deserialization filters.

Java FileChannel: Read, Write, Memory-Mapped Files, Locks

Read and write files with FileChannel and ByteBuffer, memory-map them (also beyond 2 GB), and lock file regions – with a speed comparison.

Java Performance

This category deals with the performance of Java code, i.e., with which Java means a particular task can be executed most efficiently - possibly depending on the Java version. Not only is it important to know how to optimize code, but also when it is better to leave the optimization to the Java Runtime and the Hotspot Compiler.

How to Convert int to String in Java – Which Way Is Fastest?

Convert int to String in Java: four variants benchmarked with JMH on Java 8 to 27. Which one is fastest – and why it hardly matters today.

How to Convert String to Int in Java – Peculiarities and Pitfalls

How to convert a String to an int in Java? Pitfalls, parseInt() vs. parseUnsignedInt(), int vs. Integer – with benchmarks up to Java 27.

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