1. Preview and Incubator Features
Scoped Values (Incubator) – JEP 429
Scoped values, introduced as an incubator feature in Java 20, provide a way to define values that are scoped to a specific thread or task, improving the management of context-specific data.
Scoped values provide an alternative to thread-local variables, allowing for safer and more efficient sharing of immutable data within and across threads.
Example
public class ScopedValuesExample {
public static void main(String[] args) {
ScopedValue<String> scopedValue = ScopedValue.newInstance();
ScopedValue.Scope scope = ScopedValue.withValue(scopedValue, "Hello, Java 20!");
scope.run(() -> {
System.out.println("Scoped Value: " + scopedValue.get());
});
}
}
Explanation
- Context-Specific Data: Scoped values allow developers to define values that are specific to a thread or task, improving the management of context-specific data.
- Flexibility: This feature provides more flexibility and control over the lifecycle and visibility of context-specific values.
Record Patterns (Second Preview) – JEP 432
Record patterns were reintroduced as a second preview feature in Java 20, allowing developers to match and destructure record values in a more concise and readable way.
Example
public class RecordPatternExample {
public static void main(String[] args) {
record Point(int x, int y) {}
Point point = new Point(5, 10);
if (point instanceof Point(int x, int y)) {
System.out.println("x: " + x + ", y: " + y);
}
}
}
Explanation
- Destructuring: Record patterns allow developers to destructure record values, extracting their components in a more readable way.
- Concise Code: This feature reduces boilerplate code, making it easier to work with record values.
Pattern Matching for switch (Fourth Preview) – JEP 433
Pattern matching for switch, introduced as a fourth preview feature in Java 20, allows switch statements to match patterns, providing more concise and readable code.
This feature makes it easier to express complex data queries and transformations concisely and readably.
Example
public class PatternMatchingSwitchExample {
public static void main(String[] args) {
Object obj = "Java 20";
String result = switch (obj) {
case Integer i -> "Integer: " + i;
case String s -> "String: " + s;
default -> "Unknown type";
};
System.out.println(result);
}
}
Explanation
- Concise Code: Pattern matching for
switchstatements allows for more concise and readable code, reducing boilerplate and improving maintainability. - Flexibility: This feature provides more flexibility in handling different types and patterns in
switchstatements.
Foreign Function & Memory API (Second Preview) – JEP 434
The Foreign Function & Memory API, reintroduced as a second preview feature in Java 20, provides a way to interact with native code and memory, enhancing interoperability and performance.
- Interoperability: The Foreign Function & Memory API improves interoperability with native code and memory, allowing Java applications to interact with native libraries more efficiently.
- Performance: This feature enhances performance by providing more direct access to native memory and functions.
Virtual Threads (Second Preview) – JEP 436
Virtual threads, reintroduced as a second preview feature in Java 20, provide a lightweight and scalable alternative to traditional platform threads, improving the performance and scalability of concurrent applications.
Example
import java.util.concurrent.Executors;
public class VirtualThreadsExample {
public static void main(String[] args) {
var executor = Executors.newVirtualThreadPerTaskExecutor();
executor.execute(() -> System.out.println("Hello from a virtual thread!"));
executor.shutdown();
}
}
Explanation
- Lightweight Threads: Virtual threads are lightweight and scalable, allowing for the efficient execution of many concurrent tasks.
- Improved Performance: This feature improves the performance and scalability of concurrent applications by reducing the overhead associated with traditional threads.
Structured Concurrency (Second Incubator) – JEP 437
Structured concurrency, reintroduced as an incubator feature in Java 20, simplifies the handling of concurrent tasks by grouping related tasks and managing their lifecycle as a unit.
Example
import java.util.concurrent.*;
public class StructuredConcurrencyExample {
public static void main(String[] args) throws InterruptedException, ExecutionException {
try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
Future<String> task1 = scope.fork(() -> "Task 1 result");
Future<String> task2 = scope.fork(() -> "Task 2 result");
scope.join();
scope.throwIfFailed();
System.out.println("Results: " + task1.resultNow() + ", " + task2.resultNow());
}
}
}
Explanation
- Task Grouping: Structured concurrency allows developers to group related tasks and manage their lifecycle as a unit, simplifying the handling of concurrent tasks.
- Lifecycle Management: This feature improves the reliability and maintainability of concurrent applications by providing better lifecycle management for related tasks.
2. Deprecations and Deletions
java.net.URL constructors are deprecated
Java 20 deprecates the constructors of the java.net.URL class, encouraging developers to use the java.net.URI class or factory methods instead.
Thread.suspend/resume changed to throw UnsupportedOperationException
Java 20 changes the Thread.suspend and Thread.resume methods to throw UnsupportedOperationException, as these methods are inherently unsafe and can cause deadlock issues.
Developers are encouraged to use safer alternatives for thread management, such as interrupting threads.
3. Other Changes in Java 20
Javac Warns about Type Casts in Compound Assignments with Possible Lossy Conversions
Java 20 introduces warnings in javac for type casts in compound assignments that may result in lossy conversions, helping developers identify potential issues in their code.
Idle Connection Timeouts for HTTP/2
Java 20 introduces idle connection timeouts for HTTP/2 connections, improving resource management and performance by closing idle connections.
- Resource Management: Idle connection timeouts for HTTP/2 connections improve resource management by closing idle connections, freeing up resources for other tasks.
- Performance: This feature enhances performance by ensuring that idle connections do not consume unnecessary resources.
HttpClient Default Keep Alive Time is 30 Seconds
Java 20 sets the default keep-alive time for HttpClient connections to 30 seconds, improving the management of persistent connections.
- Keep-Alive Time: Setting the default keep-alive time for
HttpClientconnections to 30 seconds improves the management of persistent connections, balancing resource usage and performance. - Resource Management: This feature enhances resource management by ensuring that connections are kept alive for a reasonable amount of time.
IdentityHashMap's Remove and Replace Methods Use Object Identity
Java 20 changes the remove and replace methods of IdentityHashMap to use object identity instead of equals for comparisons, ensuring consistent behavior with other methods of the class.
Support Unicode 15.0
Java 20 introduces support for Unicode 15.0, adding new characters, scripts, and emoji to the java.lang and java.nio packages.
- Expanded Character Set: Support for Unicode 15.0 adds new characters, scripts, and emoji, improving the ability to handle diverse character sets and languages.
- Internationalization: This feature enhances Java's internationalization capabilities, making it easier to support global applications.
Conclusion
Java 20 introduces several key features and improvements, including scoped values, record patterns, and virtual threads. These features enhance developer productivity, application performance, and the flexibility of the Java platform. By understanding and leveraging these features, developers can build more efficient and maintainable Java applications.
For a complete list of all changes in Java 20, refer to the official Java 20 release notes.
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