Java 17 Features – What Every Developer Should Know
Java 17, the latest long-term support (LTS) release before Java 21, introduced several compelling features that modernize the development experience. Whether you’re an enterprise-grade programmer, a backend architect, or a novice Java developer, Java 17 is packed with updates that can enhance code readability, maintainability, and performance.
This post covers the key features of Java 17 that every developer should know, along with practical examples and insights into why upgrading makes sense, particularly for Spring-based applications.
Table of Contents
- Sealed Classes
- Pattern Matching for instanceof
- Enhanced Switch Expressions
- Text Blocks
- Records and Compact Constructors
- Strong Encapsulation of JDK Internals
- Foreign Function & Memory API (Incubator)
- JEPs Introduced in Java 17
- Performance Improvements
- Why It Matters for Spring Apps
- FAQs
1. Sealed Classes
Sealed classes allow you to explicitly control which classes can inherit from a parent class. This feature enhances code security, maintainability, and readability by limiting potential misuse of a class’s hierarchy.
Example of Sealed Classes:
public abstract sealed class Shape permits Circle, Rectangle { }
public final class Circle extends Shape { }
public final class Rectangle extends Shape { }
Why it’s valuable:
- Makes hierarchies more predictable.
- Helps enforce domain-based models clearly.
- Prevents unwanted subclasses from being added to the inheritance chain.
2. Pattern Matching for instanceof
Java 17 removes redundant “instanceof” checks followed by manual casting by introducing pattern matching for instanceof. This simplifies your code and reduces boilerplate.
Example:
Before Java 17:
if (obj instanceof String) {
String str = (String) obj;
System.out.println(str.toUpperCase());
}
With Java 17:
if (obj instanceof String str) {
System.out.println(str.toUpperCase());
}
Why it matters: Streamlined casting leads to cleaner, safer, and more readable code.
3. Enhanced Switch Expressions
Java 17 finalizes enhanced switch expressions, allowing switch statements to return values and support new case pattern syntax.
Example:
String dayType = switch (day) {
case MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY -> "Weekday";
case SATURDAY, SUNDAY -> "Weekend";
default -> throw new IllegalArgumentException("Unknown day");
};
Advantages:
- Better readability and maintainability.
- Eliminates fall-through errors in complex switch logic.
4. Text Blocks
Introduced in earlier versions but finalized in Java 17, text blocks simplify working with multi-line strings, like JSON, HTML, or SQL.
Example:
String html = """
<html>
<body>
<h1>Welcome!</h1>
</body>
</html>
""";
Benefits:
- Improves formatting consistency.
- Avoids manual escape sequences.
5. Records and Compact Constructors
Records, introduced in Java 16, are finalized in Java 17. They’re a concise syntax for defining immutable data-carrier classes.
Example:
public record User(String name, int age) {
public User {
if (age < 0) throw new IllegalArgumentException("Age cannot be negative");
}
}
Why use records?
- Reduces boilerplate code traditionally associated with getters, equals(), toString(), and hashCode().
- Compact constructors ensure immutability while embedding validation logic.
6. Strong Encapsulation of JDK Internals
Java 17 strengthens the encapsulation of internal JDK classes and APIs, a gradual process started since JDK 9. Unsafe, internal modules can no longer be accessed without bypassing with command-line flags.
Implications:
- Developers are encouraged to use standard APIs instead of relying on internal, unsupported libraries.
- Improves application portability and security.
7. Foreign Function & Memory API (Incubator)
With the Foreign Function & Memory API, Java 17 continues to refine how developers can interact with non-Java native code like C libraries, without requiring the Java Native Interface (JNI).
Example:
try (MemorySegment segment = MemorySegment.allocateNative(100)) {
segment.set(ValueLayout.JAVA_INT, 0, 42);
int value = segment.get(ValueLayout.JAVA_INT, 0);
System.out.println(value); // Output: 42
}
Use Cases:
- Interoperability with native libraries in applications like machine learning, simulations, or cryptography.
8. JEPs Introduced in Java 17
Notable JEPs (Java Enhancement Proposals):
- JEP 356: Enhanced Pseudo-Random Number Generators
- JEP 382: New macOS/AArch64 Port
- JEP 411: Deprecate the Security Manager for Removal
These JEPs improve platform-specific optimizations, security, and randomness APIs.
9. Performance Improvements
Java 17 introduces multiple optimizations to the JVM (Java Virtual Machine):
- Faster Startup: Optimized memory handling during application startup.
- Smarter Garbage Collection: Default G1 GC aggressively optimizes memory footprint.
- New macOS Support: Enhanced compatibility with Apple M1 processors.
Why it matters: Java 17 reduces overhead for cloud-native apps, enabling cost-efficient deployments.
10. Why It Matters for Spring Apps
Java 17 brings practical benefits for Spring applications, including improved runtime performance, streamlined code constructs, and security enhancements.
Key Advantages:
- Faster Dependency Injection: Virtual threads integrate well, simplifying async processing with the Spring Framework.
- Cleaner Domain Modeling: Sealed classes and records pair seamlessly with Java Bean validation in Spring Data.
- Optimized Controller Layers: Text blocks simplify handling REST templates and responses.
Developer Tip: Pairing Spring Boot 3 with Java 17 enables full compatibility with these modern features.
FAQs
What is the significance of Java 17 as an LTS version?
Java 17, being an LTS release, guarantees long-term updates and enterprise stability, making it ideal for production use until at least 2029.
How is Java 17 different from Java 8 or 11?
Compared to Java 8/11, Java 17 includes a modernized syntax (sealed classes, records), enhanced GC performance, and stronger encapsulation of the JDK.
Should I migrate to Java 17 now or wait?
If you’re using Java 8 or 11, it’s highly recommended to migrate as soon as your libraries and frameworks support Java 17.
Summary
Java 17 solidifies its place as a must-adopt LTS version for developers. Innovations like sealed classes, pattern matching, and virtual threads make it easier to write clean, efficient, and powerful applications. When combined with performance improvements and extended runtime support, Java 17 is set to be the backbone for enterprise software over the next decade.
To explore further, check out the Java 17 Documentation and start experimenting today!
