Quick Answer
Java has evolved significantly from Java 9 to Java 21, introducing powerful features such as modules, JShell, local variable type inference, records, sealed classes, virtual threads, and sequenced collections. These features focus on improving performance, scalability, readability, and overall developer productivity in modern Java applications.
Introduction
When Java 8 was released, developers widely adopted lambda expressions, streams, and functional programming concepts. However, many developers stopped exploring Java beyond Java 8.
From Java 9 onwards, Java introduced multiple improvements at the language, API, and JVM level. These changes significantly modernized Java and made it more suitable for large-scale, high-performance, and cloud-native applications. This article explains the most important Java features from Java 9 to Java 21 that every modern Java developer should understand.
What Changed in Java After Java 8 ?
After Java 8, Java continued to evolve with a strong focus on maintainability, developer experience, and performance.
Java 8 introduced:
Lambda expressions
Streams API
Method references
From Java 9 onwards, Java introduced new programming models, APIs, and runtime enhancements that go far beyond functional programming.
What Are Java 9 Modules (JPMS) ?
Java 9 introduced the Java Platform Module System (JPMS).
What Is a Java Module?
A Java module is a group of:
Packages
Resources
A module descriptor file (
module-info.java)
Every modern Java project is treated as a module by default.
Why Do We Need Modules ?
Modules help to:
Organize large applications
Control which packages are exposed or hidden
Improve maintainability
Build modular and scalable systems
What Does module-info.java contain ?
The module descriptor defines:
Module name
Dependencies (
requires)Exported packages (
exports)Services used (
uses)Services provided (
provides with)Reflection permissions
What Is JShell in Java 9 ?
JShell is an interactive tool introduced in Java 9.
JShell allows developers to:
Execute Java code snippets instantly
Run Java statements without creating a class
Learn and test Java concepts quickly
It works as a REPL (Read–Evaluate–Print Loop), similar to JavaScript consoles.
What Is Local Variable Type Inference (var) in Java 10 ?
Java 10 introduced local variable type inference using the var keyword.
Key Points About var
Used only for local variables
Must be initialized during declaration
Cannot be assigned
nullCannot be used for instance or static variables
Important Note:var is not dynamic typing. Once the type is inferred, it cannot change.
What New String Utility Methods Were Added in Java 11 ?
Java 11 enhanced the String class with new utility methods:
isBlank()strip(),stripLeading(),stripTrailing()repeat(int)lines()
These methods reduce boilerplate code and improve readability.
What Are Switch Expressions in Java 14 ?
Java 14 introduced switch expressions that:
Return values directly
Do not require
breakstatementsSupport arrow (
->) syntaxRequire a
defaultcase
Switch expressions make conditional logic more concise and expressive.
What Are Text Blocks in Java 15 ?
Text blocks allow multi-line strings using triple double quotes (""").
Common Use Cases
SQL queries
JSON payloads
HTML templates
Multi-line text
Text blocks eliminate string concatenation and improve code readability.
EXAMPLE - SQL queries
String sql = """
SELECT id, name, email
FROM users
WHERE active = true
ORDER BY name
""";
EXAMPLE - JSON payloads
String json = """
{
"id": 101,
"name": "John",
"email": "john@example.com"
}
""";
EXAMPLE - HTML templates
String html = """
<html>
<body>
<h1>Welcome</h1>
<p>Hello User</p>
</body>
</html>
""";
EXAMPLE - Multi-line text
String message = """
Dear User,
Your account has been successfully created.
Thank you for registering.
""";
What Are Records in Java 16 ?
Records are immutable data carrier classes designed to reduce boilerplate code.
Characteristics of Records
- Automatically generate constructor, getters,
toString,equals, andhashCode - Immutable (no setters)
- Cannot extend other classes
Where Are Records Used?
DTOs
API request and response objects
Value objects
What Are Sealed Classes in Java 17 ?
Sealed classes restrict which classes can extend or implement them.
Purpose of Sealed Classes
Enforce controlled inheritance
Maintain clean and predictable class hierarchies
Subclasses must be declared as:
finalsealednon-sealed
What Are Virtual Threads in Java 21 ?
Virtual threads are lightweight threads managed by the JVM instead of the operating system.
When to Use Virtual Threads
IO-bound operations
Database calls
HTTP requests
High-concurrency microservices
When NOT to Use Virtual Threads
CPU-intensive tasks
Long-running blocking operations
Virtual threads improve scalability without overloading the OS.
What Is the Sequenced Collection API in Java 21 ?
Java 21 introduced:
SequencedCollectionSequencedSetSequencedMap
Benefits
Uniform API for ordered collections
Methods like
addFirst()andaddLast()Easy access using
getFirst()andgetLast()Supports reversible views
These APIs improve consistency across Java collections.
Frequently Asked Questions (FAQ)
What are the most important Java features after Java 8?
Modules, JShell, var, records, sealed classes, virtual threads, and sequenced collections are among the most important features.
Are Java modules mandatory?
Yes. All modern Java projects are treated as modules by default..
Are records immutable?
Yes. Records are immutable and do not support setter methods.
What are virtual threads used for ?
Virtual threads are best suited for IO-bound and high-concurrency applications.
Should developers learn Java features after Java 8 ?
Yes. Modern Java development requires understanding features introduced after Java 8.
Final Thoughts
Java has evolved significantly beyond Java 8. Modern Java focuses on modularity, readability, scalability, and performance.
Understanding Java features from Java 9 to Java 21 is essential for writing high-quality code and staying relevant as a modern Java developer.
👉 Start using these features gradually in your current projects.