Java 19 Features

Java 19 introduced several new features and enhancements aimed at improving the language and runtime. This guide will cover the important features introduced in Java 19, along with examples to illustrate how they work. We will explore new methods for creating preallocated HashMaps, preview and incubator features, deprecations, deletions, and other changes that have been made.

1. New Methods to Create Preallocated HashMaps

Java 19 introduces new factory methods to create preallocated HashMap instances. These methods help improve performance by reducing the need for resizing when the expected number of entries is known in advance.

Example: Creating Preallocated HashMap

import java.util.HashMap;

public class PreallocatedHashMapExample {
    public static void main(String[] args) {
        // Create a preallocated HashMap with an initial capacity of 20
        HashMap<String, Integer> map = HashMap.newHashMap(20);

        // Add elements to the HashMap
        map.put("One", 1);
        map.put("Two", 2);
        map.put("Three", 3);

        // Print the HashMap
        System.out.println("HashMap: " + map);
    }
}

Explanation:

• HashMap.newHashMap(20) creates a HashMap with an initial capacity of 20, reducing the need for resizing as elements are added.

2. Preview and Incubator Features

Java 19 includes several preview and incubator features that allow developers to experiment with new functionalities that may become permanent in future releases.

Pattern Matching for switch (Third Preview) – JEP 427

Pattern Matching for switch allows for more expressive and readable code by enabling the switch statement to match patterns, rather than just values.

Example: Pattern Matching for switch

public class PatternMatchingSwitchExample {
    public static void main(String[] args) {
        Object obj = "Hello, Java 19";

        // Using pattern matching in switch statement
        switch (obj) {
            case Integer i -> System.out.println("Integer: " + i);
            case String s -> System.out.println("String: " + s);
            case Double d -> System.out.println("Double: " + d);
            default -> System.out.println("Unknown type");
        }
    }
}

Explanation:

• The switch statement uses pattern matching to handle different types (Integer, String, Double) directly, improving code clarity.

Record Patterns (Preview) – JEP 405

Record patterns enhance pattern matching by allowing records to be deconstructed in patterns. This feature is useful for working with data classes.

Example: Record Patterns

record Point(int x, int y) {}

public class RecordPatternsExample {
    public static void main(String[] args) {
        Point point = new Point(10, 20);

        // Using record pattern to deconstruct a record
        if (point instanceof Point(int x, int y)) {
            System.out.println("Point coordinates: (" + x + ", " + y + ")");
        }
    }
}

Explanation:

• if (point instanceof Point(int x, int y)) deconstructs the Point record into its components x and y.

Virtual Threads (Preview) – JEP 425

Virtual threads are lightweight threads that aim to simplify writing, maintaining, and observing high-throughput concurrent applications.

Example: Virtual Threads

public class VirtualThreadsExample {
    public static void main(String[] args) {
        // Create and start a virtual thread
        Thread vThread = Thread.ofVirtual().start(() -> {
            System.out.println("Running in a virtual thread");
        });

        // Wait for the virtual thread to complete
        vThread.join();
    }
}

Explanation:

• Thread.ofVirtual().start() creates and starts a virtual thread, allowing for high-throughput concurrency with minimal resource overhead.

Structured Concurrency (Incubator) – JEP 428

Structured Concurrency introduces a library for managing the lifecycle of multiple concurrent tasks with a clear structure, improving reliability and readability.

Example: Structured Concurrency

import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.Future;

public class StructuredConcurrencyExample {
    public static void main(String[] args) throws Exception {
        ExecutorService executor = Executors.newVirtualThreadPerTaskExecutor();

        try (executor) {
            Future<String> task = executor.submit(() -> {
                // Simulate a task
                Thread.sleep(1000);
                return "Task completed";
            });

            System.out.println(task.get());
        }
    }
}

Explanation:

• Executors.newVirtualThreadPerTaskExecutor() creates an executor service for managing virtual threads, allowing for efficient execution of concurrent tasks.

Foreign Function & Memory API (Preview) – JEP 424

The Foreign Function & Memory API provides a safe and efficient way to work with foreign memory and interact with native code.

Example: Foreign Function & Memory API

import jdk.incubator.foreign.*;

public class ForeignFunctionMemoryExample {
    public static void main(String[] args) {
        try (MemorySegment segment = MemorySegment.allocateNative(1024)) {
            System.out.println("Allocated native memory segment of size: " + segment.byteSize());
        }
    }
}

Explanation:

• MemorySegment.allocateNative(1024) allocates a native memory segment of size 1024 bytes, providing safe access to foreign memory.

Vector API (Fourth Incubator) – JEP 426

The Vector API allows developers to express vector computations that compile to optimal vector instructions on supported hardware, enhancing performance.

Example: Vector API

import jdk.incubator.vector.*;

public class VectorAPIExample {
    public static void main(String[] args) {
        // Create a vector species of type int with size 256
        VectorSpecies<Integer> SPECIES = IntVector.SPECIES_256;

        // Initialize two int arrays
        int[] a = {1, 2, 3, 4, 5, 6, 7, 8};
        int[] b = {8, 7, 6, 5, 4, 3, 2, 1};

        // Perform vector addition
        IntVector va = IntVector.fromArray(SPECIES, a, 0);
        IntVector vb = IntVector.fromArray(SPECIES, b, 0);
        IntVector vc = va.add(vb);

        // Store the result in an array
        int[] c = new int[8];
        vc.intoArray(c, 0);

        // Print the result
        System.out.println("Vector addition result: " + Arrays.toString(c));
    }
}

Explanation:

• The Vector API allows for vectorized computations, enabling efficient execution of operations on supported hardware.

3. Deprecations and Deletions

Deprecation of Locale Class Constructors

The constructors in the Locale class have been deprecated to encourage the use of factory methods like Locale.of().

Example: Using Locale.of()

import java.util.Locale;

public class LocaleExample {
    public static void main(String[] args) {
        // Create a Locale using the factory method
        Locale locale = Locale.of("en", "US");
        System.out.println("Locale: " + locale);
    }
}

Explanation:

• Locale.of("en", "US") is the recommended way to create a Locale instance, replacing deprecated constructors.

java.lang.ThreadGroup is Degraded

The ThreadGroup class is now deprecated, as its functionality is considered obsolete for modern Java applications.

4. Other Changes in Java 19

Automatic Generation of the CDS Archive

Java 19 automatically generates the Class Data Sharing (CDS) archive during the JDK build process, improving startup performance.

Linux/RISC-V Port – JEP 422

Java 19 includes a port of the JDK to the Linux/RISC-V architecture, expanding the platforms supported by Java.

Additional Date-Time Formats

Java 19 introduces additional date-time formats, providing more flexibility in parsing and formatting dates and times.

import java.time.LocalDateTime;
import java.time.format.DateTimeFormatter;

public class DateTimeFormatsExample {
    public static void main(String[] args) {
        LocalDateTime dateTime = LocalDateTime.now();
        
        // Format date-time with additional formats
        DateTimeFormatter formatter = DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss");
        String formattedDateTime = dateTime.format(formatter);
        
        System.out.println("Formatted Date-Time: " + formattedDateTime);
    }
}

Explanation:

• DateTimeFormatter.ofPattern("yyyy-MM-dd HH:mm:ss") allows for custom formatting of date-time strings using additional formats.

New System Properties for System.out and System.err

Java 19 introduces new system properties for configuring the behavior of System.out and System.err, enhancing control over standard output and error streams.

5. Summary

Java 19 introduces a range of features and improvements that enhance the language, runtime, and developer experience. From preallocated HashMap methods to preview features like pattern matching, record patterns, and virtual threads, Java 19 offers exciting new capabilities for developers to explore. Additionally, Java 19 includes various deprecations, deletions, and other changes that improve performance, flexibility, and usability across the platform. Understanding these new features will help developers take full advantage of Java 19 in their applications.

For a complete list of all changes, refer to the official Java 19 release notes.

Series: Java Release-wise New Features

• Java 8 Features
• Java 9 Features
• Java 10 Features
• Java 11 Features
• Java 12 Features
• Java 13 Features
• Java 14 Features
• Java 15 Features
• Java 16 Features
• Java 17 Features
• Java 18 Features
• Java 19 Features
• Java 20 Features
• Java 21 Features