Java continues to evolve rapidly, and Java 15 introduced several exciting enhancements focused on developer productivity, modern programming practices, and JVM improvements.

Although Java 15 is a non-LTS release, it introduced important preview features and performance improvements that shaped later Java versions.

In this article, we will explore the major Java 15 features with examples and real-world use cases.

Why Java 15 Matters

Java 15 focused on:

Cleaner syntax
Better developer productivity
Modern programming support
Improved memory management
Enhanced JVM capabilities

Many features introduced in Java 15 later became stable in newer Java releases.

Major Features in Java 15

1. Text Blocks (Standard Feature)

One of the most useful additions in Java 15 is:

Text Blocks

Text Blocks simplify writing multiline strings.

Before Java 15

String json = "{\n" +
              "  \"name\": \"Susil\",\n" +
              "  \"age\": 30\n" +
              "}";

Java 15 Text Block

String json = """
    {
      "name": "Susil",
      "age": 30
    }
    """;

Benefits

Cleaner code
Better readability
Easier JSON/XML/SQL handling
Reduced escape characters

Real-World Use Cases

REST API payloads
SQL queries
HTML templates
JSON generation
SOAP XML requests

SQL Example

String query = """
    SELECT id, name
    FROM employee
    WHERE department = 'IT'
    """;

2. Sealed Classes (Preview)

Sealed Classes allow developers to restrict which classes can extend or implement a class/interface.

Example

public sealed class Vehicle
    permits Car, Bike {
}

final class Car extends Vehicle {
}

final class Bike extends Vehicle {
}

Benefits

Better domain modeling
Improved maintainability
Stronger inheritance control
Safer APIs

Real-World Use Cases

Banking systems
Payment processing
Rule engines
Domain-driven design

3. Hidden Classes

Java 15 introduced Hidden Classes mainly for frameworks and runtime-generated classes.

Benefits

Better framework performance
Improved runtime efficiency
Reduced classloader pollution

Used By

Spring Framework
Hibernate
ByteBuddy
Proxy libraries

4. Records (Second Preview)

Records reduce boilerplate code for data carrier classes.

Traditional POJO

public class Employee {

    private final int id;
    private final String name;

    public Employee(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public String getName() {
        return name;
    }
}

Java Record

public record Employee(int id, String name) {
}

Benefits

Less boilerplate
Immutable data objects
Cleaner code
Better readability

Excellent For

DTOs
API models
Kafka events
Configuration objects

5. Pattern Matching for instanceof (Second Preview)

Java 15 improved instanceof usage.

Old Style

if (obj instanceof String) {
    String s = (String) obj;
    System.out.println(s.length());
}

Java 15 Style

if (obj instanceof String s) {
    System.out.println(s.length());
}

Benefits

Cleaner code
Reduced casting
Better readability
Safer type handling

6. Edwards-Curve Digital Signature Algorithm (EdDSA)

Java 15 added support for modern cryptographic signatures.

Benefits

Better security
Faster cryptographic operations
Modern digital signatures

Useful For

Secure APIs
JWT signing
Authentication systems
Blockchain applications

7. Foreign-Memory Access API (Incubator)

This API improves access to off-heap memory safely.

Benefits

Better performance
Safer native memory access
Alternative to unsafe operations

Useful For

High-performance systems
Big data applications
AI/ML systems
Native integrations

8. ZGC Improvements

Java 15 improved the:

Z Garbage Collector (ZGC)

Improvements

Better scalability
Lower pause times
Improved memory handling

Excellent For

Large enterprise applications
Microservices
Cloud-native systems
Real-time systems

9. Shenandoah Garbage Collector Improvements

Java 15 further enhanced Shenandoah GC.

Benefits

Reduced pause times
Faster response times
Better memory management

10. Nashorn JavaScript Engine Removed

The old Nashorn JavaScript engine was removed in Java 15.

Why Removed?

Better alternatives exist
Maintenance complexity
Modern JavaScript engines available externally

Alternatives

GraalVM JavaScript
Node.js integration
External scripting engines

Performance Improvements in Java 15

Java 15 improved:

JVM startup
Garbage collection
Memory management
Runtime performance
Dynamic class loading

Java 15 for Spring Boot Developers

Java 15 works well with:

Enterprise Benefits

Java 15 Feature	Enterprise Benefit
Text Blocks	Cleaner SQL/JSON/XML
Records	Better DTO modeling
Pattern Matching	Cleaner business logic
ZGC	Better scalability
Sealed Classes	Safer domain design

Java 15 vs Java 11

Feature	Java 11	Java 15
Text Blocks	No	Yes
Records	No	Preview
Sealed Classes	No	Preview
Pattern Matching	No	Improved
Hidden Classes	No	Yes

Maven Configuration for Java 15

<properties>
    <maven.compiler.source>15</maven.compiler.source>
    <maven.compiler.target>15</maven.compiler.target>
</properties>

Gradle Configuration

java {
    toolchain {
        languageVersion = JavaLanguageVersion.of(15)
    }
}

Enable Preview Features

Some Java 15 features are preview features.

Maven

<compilerArgs>
    --enable-preview
</compilerArgs>

Run Application

java --enable-preview Main.java

Should You Upgrade to Java 15?

Upgrade If You Want

Modern Java syntax
Better developer productivity
Improved performance
Latest JVM enhancements

Stay on LTS If You Need

Long-term enterprise stability
Production-grade support
Enterprise certification

Recommended LTS versions:

Java 11
Java 17
Java 21

Final Thoughts

Java 15 introduced several important improvements that modernized Java development significantly.

Features like:

Text Blocks
Records
Pattern Matching
Sealed Classes

made Java cleaner, safer, and more expressive.

Even though Java 15 is not an LTS release, many of its innovations became foundational for future Java versions.

If you are a Java developer working on:

Spring Boot applications
Enterprise APIs
Microservices
Cloud-native systems

then understanding Java 15 is extremely valuable.