02-modern-syntax

Module 02: Modern Java Syntax

Companion code for Article 2: "Modern Java Syntax: Records, Pattern Matching, and var"

Overview

This module provides comprehensive examples of modern Java syntax features introduced since Java 8.

Features Covered

1. Records (records/)

Records are immutable data carriers with automatic implementations.

Feature	Description
Compact constructor	Validation without repeating parameters
Automatic accessors	record.name() instead of record.getName()
Automatic equals/hashCode	Based on all components
Local records	Define records inside methods
Generic records	Type parameters work naturally

Files:

• RecordBasics.java - Simple records, validation, nested records
• RecordAdvanced.java - Generics, interfaces, static factories, local records

2. Pattern Matching (patterns/)

Pattern matching eliminates casts and enables type-safe switching.

Feature	Description
instanceof patterns	Bind variable in same expression
Switch expressions	Return values from switch
Switch patterns	Match types and deconstruct
Record patterns	Extract components in patterns
Guards (when)	Additional conditions in patterns

Files:

• PatternMatchingBasics.java - instanceof, switch expressions, null handling
• RecordPatterns.java - Deconstruction, nesting, guards, exhaustiveness

3. Local Variable Type Inference (var/)

The var keyword reduces redundancy without sacrificing type safety.

Use Case	Recommendation
Complex generics	Highly recommended
Constructor calls	Recommended
For-each loops	Recommended
Method returns	Use when type is obvious
Numeric literals	Avoid (ambiguous)

Files:

• LocalVariableTypeInference.java - Best practices, limitations, examples

4. Text Blocks (textblocks/)

Multi-line string literals without concatenation or excessive escaping.

Feature	Description
Multi-line	No \n concatenation needed
Indentation	Relative to closing """
No quote escaping	" works without \"
\s	Preserve trailing whitespace
\ at line end	Suppress newline

Files:

• TextBlocks.java - SQL, JSON, regex, code generation examples

Running the Examples

# Run all examples in this module
./gradlew :02-modern-syntax:run

# Or run specific classes
./gradlew :02-modern-syntax:run --args="records.RecordBasics"

JEPs Referenced

JEP	Feature	Java Version
JEP 286	Local Variable Type Inference (var)	Java 10
JEP 361	Switch Expressions	Java 14
JEP 378	Text Blocks	Java 15
JEP 394	Pattern Matching for instanceof	Java 16
JEP 395	Records	Java 16
JEP 409	Sealed Classes	Java 17
JEP 440	Record Patterns	Java 21
JEP 441	Pattern Matching for switch	Java 21

Quick Reference

// Record with validation
record Customer(String id, String name) {
    public Customer {
        Objects.requireNonNull(id);
    }
}

// Pattern matching with guards
String describe(Object obj) {
    return switch (obj) {
        case String s when s.length() > 10 -> "Long string";
        case String s -> "Short string: " + s;
        case Integer i when i > 0 -> "Positive: " + i;
        case null -> "null";
        default -> "Unknown";
    };
}

// Record deconstruction
double area(Shape shape) {
    return switch (shape) {
        case Circle(double r) -> Math.PI * r * r;
        case Rectangle(double w, double h) -> w * h;
    };
}

// var with complex generics
var grouped = items.stream()
    .collect(Collectors.groupingBy(Item::category));

// Text block
String json = """
    {"name": "%s", "age": %d}
    """.formatted(name, age);

Next Steps

After mastering modern syntax, proceed to:

• Module 03 - Data-Oriented Programming (applying these features to domain modeling)
• Module 04 - Functional Patterns (combining with lambdas and streams)