Exploring Java 17 LTS Features

By John Developer

June 10, 2025

Java LTS Releases

Java 17, released in September 2021, is a Long-Term Support (LTS) release that brings several exciting features and improvements to the Java ecosystem. As an LTS release, Java 17 will receive updates and support for an extended period, making it an important milestone for Java developers. In this post, we'll explore the key features introduced in Java 17 and how they can enhance your Java development experience.

Sealed Classes and Interfaces

One of the most significant features introduced in Java 17 is sealed classes and interfaces. This feature provides a way to restrict which other classes or interfaces may extend or implement them, giving developers more control over their class hierarchies.

// A sealed class with permitted subclasses
public sealed class Shape permits Circle, Rectangle, Triangle {
    // Common shape methods and properties
}

// Permitted subclasses must be either final, sealed, or non-sealed
public final class Circle extends Shape {
    private final double radius;
    
    public Circle(double radius) {
        this.radius = radius;
    }
    
    // Circle-specific methods
}

public final class Rectangle extends Shape {
    private final double width;
    private final double height;
    
    public Rectangle(double width, double height) {
        this.width = width;
        this.height = height;
    }
    
    // Rectangle-specific methods
}

public final class Triangle extends Shape {
    // Triangle implementation
}

Sealed classes provide several benefits:

• Pattern Matching Enhancement: They work well with pattern matching, as the compiler knows all possible subtypes.
• Better API Design: They allow library designers to clearly express which classes are meant to be extended.
• Controlled Hierarchy: They prevent unexpected or unwanted extensions of your classes.

Pattern Matching for switch (Preview)

Java 17 includes a preview feature for pattern matching in switch expressions and statements. This feature extends the expressiveness and applicability of switch expressions by allowing patterns to appear in case labels.

// Pattern matching for switch
Object obj = // some object;
String formatted = switch (obj) {
    case Integer i -> String.format("int %d", i);
    case Long l    -> String.format("long %d", l);
    case Double d  -> String.format("double %f", d);
    case String s  -> String.format("String %s", s);
    case null      -> "null";
    default        -> obj.toString();
};

This feature simplifies code that performs different actions based on the type of an object, making it more readable and less error-prone.

Records

Records, which were previewed in earlier versions, are now a standard feature in Java 17. Records provide a compact syntax for declaring classes that are transparent holders for shallowly immutable data.

// A simple record
public record Person(String name, int age) {
    // Compact constructor for validation
    public Person {
        if (age < 0) {
            throw new IllegalArgumentException("Age cannot be negative");
        }
    }
    
    // You can add methods to records
    public boolean isAdult() {
        return age >= 18;
    }
}

Records automatically provide:

• A constructor for all fields
• Accessor methods for all fields
• equals() and hashCode() implementations
• A toString() method

This feature significantly reduces boilerplate code for data carrier classes, making your code more concise and readable.

Strong Encapsulation of JDK Internals

Java 17 completes the strong encapsulation of JDK internals that began in Java 9. This means that internal APIs that were previously accessible are now fully encapsulated and inaccessible by default.

While this might require some adjustments for code that relied on internal APIs, it's a positive change for the Java ecosystem as it:

• Improves security by reducing the attack surface
• Enables the JDK to evolve more freely without breaking existing code
• Encourages the use of supported, public APIs

Enhanced Pseudo-Random Number Generators

Java 17 introduces new interfaces and implementations for pseudo-random number generators (PRNGs). The new API makes it easier to use different PRNG algorithms interchangeably and to request a stream of random values.

// Using the new random number generator API
RandomGenerator generator = RandomGenerator.of("L64X128MixRandom");
int randomInt = generator.nextInt(100); // Random int between 0 and 99

// Stream of random values
DoubleStream randomDoubles = generator.doubles(10); // Stream of 10 random doubles

Context-Specific Deserialization Filters

Java 17 enhances the serialization filtering mechanism introduced in earlier versions by allowing the specification of filters at the JVM level and in a dynamic, context-specific manner. This improves security by providing more control over what classes can be deserialized.

Deprecations and Removals

Java 17 also includes several deprecations and removals:

• The Applet API has been deprecated for removal
• The Security Manager has been deprecated for removal
• The experimental AOT and JIT compiler have been removed

Performance Improvements

Java 17 includes various performance improvements, including:

• Enhanced garbage collection with the new ZGC (Z Garbage Collector)
• Improved startup time
• Better performance for common operations

Conclusion

Java 17 is a significant LTS release that brings many valuable features and improvements to the Java platform. From sealed classes to records, pattern matching for switch, and enhanced random number generators, these features make Java development more productive, secure, and enjoyable.

As a long-term support release, Java 17 is a solid foundation for Java applications that will be maintained for years to come. If you haven't already, it's worth exploring these features and considering an upgrade to Java 17 for your projects.

John Developer

John is a senior Java developer with over 10 years of experience in enterprise application development. He is passionate about Java and enjoys exploring new features and best practices.