Compare Java Objects Without Getters: reflectionEquals()
Learn to compare Java objects without getters or equals() using EqualsBuilder.reflectionEquals(), excluded fields, recursive mode and AssertJ.
These java basic tutorials in intended for absolute beginners. If you are just beginning to learn java, you should go through these tutorials, otherwise skip them.
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Java Math.divideExact(): Detect Integer Division Overflow
Learn how Math.divideExact() in Java detects the Integer.MIN_VALUE / -1 overflow, how it handles zero, and how it compares to floorDivExact().
Java Math.abs() vs Math.absExact(): Overflow Explained
Java Math.abs() vs Math.absExact() with examples. Why Math.abs(Integer.MIN_VALUE) is negative, when absExact() throws, and safe alternatives.
Decimal to Hexadecimal Conversion: Examples and Java Code
To convert decimal to hexadecimal, divide by 16 repeatedly and read the remainders in reverse, so 269 becomes 10D. See a worked division table, a table of common conversion examples, and the Java one-liners for both directions.
Builder Pattern for Java Records: Nested, Lombok, RecordBuilder
Learn the builder pattern for Java records with a nested builder, Lombok @Builder and RecordBuilder, plus defaults, validation and with methods on Java 25.
Java Keywords List: Reserved and Contextual Keywords (Java 25)
The full list of Java keywords as of Java 25, with 51 reserved and 17 contextual keywords grouped by category, literals, version history and rules.
Convert an Object to Map in Java: Jackson, Gson and Reflection
Convert an object to Map in Java with Jackson 3 convertValue(), JavaPropsMapper flat keys, Gson and reflection, plus nulls, records and Map back to object.
Round a Double to 2 Decimal Places in Java (or N Places)
Learn how to round a double to 2 decimal places in Java with BigDecimal, Math.round(), String.format() and DecimalFormat, plus rounding modes and pitfalls.
Java printf() and String.format(): Format Specifier Guide
Java printf examples for %s, %d, %.2f, width, flags, dates and locales, plus String.format(), formatted() and fixes for common format exceptions.
Ternary Operator in Java: Syntax, Examples and Pitfalls
The ternary operator in Java with examples covering syntax, result types, the null unboxing trap, nested ternaries and when to use if-else instead.
Java Cleaner API: Replace finalize() with Cleaner
Learn the Java Cleaner API with a native memory example, the mistakes that stop cleanup, and how to migrate deprecated finalize() code in Java 25.
Java Core & Fundamentals Tutorial
Java tutorial for beginners on Java 25. Install the JDK, run a first program and follow a 12-step learning path plus an index of every Java topic.
How to Install Java on 64-bit Windows (JDK 25 Guide)
Install Java on 64-bit Windows with JDK 25 using the MSI, ZIP or winget, set JAVA_HOME and Path, verify java -version and check 32-bit vs 64-bit.
Java Hello World Program: Java 25 and Classic Versions
Java Hello World program for Java 25 and older versions, with javac and java commands, real output, a line-by-line walkthrough and fixes for common errors.
Pattern Matching for instanceof in Java (Java 16 to 25)
Pattern matching for instanceof in Java with type patterns, flow scoping, null and generics rules, equals() examples, record patterns and Java 25 updates.
Java Naming Conventions for Classes, Methods and Variables
Java naming conventions for packages, classes, methods, variables, constants and generics, with identifier rules, examples, a refactoring and style guides.
Java hashCode() and equals(): Contract, Examples, Records
Learn how Java hashCode and equals work, the contract between them, why HashSet breaks when only equals() is overridden, plus records and mutable keys.
Java Wrapper Classes: Autoboxing, Unboxing and Pitfalls
Java wrapper classes explained with autoboxing and unboxing, valueOf() vs parseInt(), the Integer cache, == and null pitfalls, and examples on Java 25.
Java var Keyword: Local Variable Type Inference Explained
Java var keyword explained with Java 25 examples. See where local variable type inference works, which javac errors it causes, and common mistakes.
Java Comments: Single-Line, Multi-Line and Javadoc
Java comments explained with single-line, multi-line and Javadoc examples, Markdown doc comments from Java 23, javadoc tags, shortcuts and good practice.
Java Variables: Types, Scope, var and Default Values
Java variables explained with examples of local, instance and static variables, default values, scope, var, final and naming rules in Java 25.
Difference Between JDK, JRE and JVM in Java (Java 25)
Learn the difference between JDK, JRE and JVM in Java 25, what each one contains, how class loaders and the JIT work and why Oracle ships no JRE.
Java Modules Tutorial: JPMS and module-info.java Explained
Java modules tutorial for Java 25. Write module-info.java, use requires, exports, opens and services, fix module errors, and build with jlink.
JShell Tutorial: Java REPL Commands With Examples
JShell tutorial for Java 25. Run Java snippets without a class, use /vars, /list, /save and /open, add JARs, run scripts and learn the default imports.
Java Classpath: How to Set It With -cp and CLASSPATH
Learn how the Java classpath works, set it with -cp or CLASSPATH on Windows and Linux, use lib/* wildcards, fix NoClassDefFoundError, compare sourcepath.
Java System Properties: getProperty, -D and the Key List
Java system properties in Java 25 with the standard key list, System.getProperty with defaults, -D options, setProperty and environment variables.
Static Import in Java: Syntax, Rules and When to Use It
Static import in Java explained with single and on-demand forms, name clash and shadowing rules, JUnit examples, best practices and Java 25 compact files.
Java Class and Object: Differences, Creation and Examples
Learn the difference between a Java class and object, how to write a class, create objects with new, the initialization order and the kinds of classes.
Block Statement in Java: Braces, Scope and Initializers
A block statement in Java groups statements in braces. Learn block scope, the missing-brace bug, static and instance initializer blocks and labels.
Types of Statements in Java With Examples (Java 21)
Every type of statement in Java with a short example: declaration, expression, control flow, jump, block, empty, try, synchronized, labeled and assert statements, plus switch expressions, yield and pattern matching in switch.
Operators in Java: Types, Precedence and Examples
Operators in Java with examples for arithmetic, logical, bitwise, assignment and instanceof operators, plus the precedence table and common traps.
Little Endian vs Big Endian in Java with ByteBuffer Examples
Little endian vs big endian explained for Java developers. See Java’s default byte order and read little-endian data with ByteBuffer and reverseBytes().
Data Types in Java: Primitive vs Reference with Examples
Data types in Java with examples covering the 8 primitive types, sizes and ranges, reference types, literals, wrapper classes and choosing a type.
Introduction to Java Programming Language (Java 25)
Introduction to Java programming language covering bytecode and the JVM, JDK vs JRE, Java 25 LTS, versions, features, uses and a first program to run.
Java Primitive Data Types: Sizes, Ranges and Defaults
Java has eight primitive data types that hold plain values, not object references. Sizes, ranges, defaults, literals, overflow, floating-point precision, casting rules and wrapper classes, with tested Java 25 examples.
java.exe vs javaw.exe: What Is javaw.exe and When to Use It
java.exe vs javaw.exe on Windows, the console and GUI launchers compared, with output and exit codes, javaw.exe in Task Manager and when to use each.
Detect Integer Overflow in Java with Math Exact Methods
Integer overflow in Java wraps values without an error. Detect it with Math.addExact, multiplyExact and toIntExact, and avoid it with long and BigInteger.
javap: View Bytecode of a Java Class File
Use javap to view the bytecode of a Java class file. Learn -c, -p, -v and -l with real JDK 25 output, JAR classes, IDE viewers and the ClassFile API.
Java Is Pass-by-Value, Not Pass-by-Reference: Examples
Java pass by value explained with primitives, object references, swap(), Strings, arrays and lists, plus how to return changed values from a method.
Java main() Method: Syntax, Java 25 Rules and Arguments
Java main method explained with the classic signature, Java 25 instance main methods, launcher errors, command-line arguments, parsing and exit codes.
Immutable Class in Java: Rules, Examples and Records
Learn how to create an immutable class in Java with final fields, defensive copies and List.copyOf(), plus records, unmodifiable views and thread safety.
