# Must-Know Features in JDK 23: What’s New for Java Developers? 🚀

Java enthusiasts and developers, rejoice! As the programming world eagerly anticipates the latest advancements in Java Development Kit (JDK), JDK 23 iS set to bring transformative features that promise to elevate your coding experience to new heights. From improved performance to enhanced syntax, these upcoming releases are packed with exciting updates. Let’s dive into the top 10 features that you need to know about JDK 23. 🌟

Release Dates and Versions of JDK 23

JDK 23 is a part of the Java SE (Standard Edition) platform, continuing Oracle’s commitment to providing a regular, predictable release schedule with feature updates every six months. Here’s a brief overview of the release dates and versions for JDK 23:

Release Dates:

• Early Access Builds: Development of JDK 23 began with early access builds available to developers and testers. These builds are released frequently during the development cycle to provide early access to new features, enhancements, and bug fixes. Developers can download these builds from the OpenJDK website and provide feedback to help stabilize the final release.

• Feature Freeze: The Feature Freeze date for JDK 23 was typically scheduled around early 2024. This is the point in the development cycle when no new features are added, and the focus shifts to bug fixing and stabilization.

• General Availability (GA): The General Availability (GA) release of JDK 23 is planned for September 2024. This is the final, production-ready version of JDK 23, suitable for use in production environments.

JDK Features or APIs States

Java’s development process involves several stages for introducing new features and APIs. These stages ensure that any changes to the language, libraries, or runtime are well thought out, thoroughly tested, and refined based on community feedback before they become part of the official Java SE standard. Here is an explanation of all the stages:

1. Incubator Stage

Purpose:

The incubator stage is the earliest stage for experimental APIs or tools that are not yet part of the Java SE specification. This stage allows developers to try out new, non-final APIs, provide feedback, and influence their design and implementation.

Characteristics:

• Experimental: The APIs are still in a very early stage and may undergo significant changes or even be withdrawn entirely.

• Not Part of Java SE: Incubator modules are not considered part of the official Java SE standard. They are excluded from the Java SE specification.

• Requires Explicit Enablement: Developers need to explicitly enable incubator modules in their projects to use these APIs, signaling that they are aware of their experimental nature.

2. Preview Stage

Purpose:

The preview stage is the next step after the incubator phase. Features in the preview stage are more mature than incubator APIs, but they are not yet finalized. The goal of this stage is to provide a fully specified version of the feature to the Java community to try out and provide feedback.

Characteristics:

• Nearly Complete: Preview features are generally close to their final form but are not guaranteed to remain unchanged.

• Part of Java SE for Testing: Unlike incubator modules, preview features are considered part of the Java SE platform but are marked as non-final.

• Requires Explicit Enablement: Developers must enable preview features explicitly using command-line options (e.g., – enable-preview) when compiling or running code that uses them.

Multiple Previews:

• A feature can go through multiple preview cycles (e.g., “first preview,” “second preview”) if further refinement is needed based on community feedback. Each preview provides an opportunity to gather more feedback and make adjustments.

3. Stable/Final Stage

Purpose:

The stable or final stage represents the culmination of feedback, testing, and iteration. At this stage, a feature has been finalized and is considered a permanent part of the Java SE platform.

Characteristics:

• Fully Integrated: The feature is fully integrated into the Java SE platform and is no longer marked as experimental or non-final.

• No Special Enablement Required: Stable features do not require any special flags or options to be used – they are enabled by default.

• Backward Compatibility Commitment: The feature is guaranteed to remain compatible in future Java versions unless explicitly deprecated, following Java’s compatibility guidelines.

Examples:

• Features like Local-Variable Type Inference (var) in Java 10, Switch Expressions in Java 14, and Records in Java 16 eventually became stable features after undergoing preview stages.

4. Deprecation

Purpose:

The deprecation stage is used to mark features, APIs, or tools that are considered outdated or no longer recommended for use. Deprecation is a signal to developers that a feature is likely to be removed in a future release.

Characteristics:

• Marked as Deprecated: Deprecated features are explicitly marked in the JDK documentation and source code annotations (e.g., @deprecated annotation).

• Still Functional: Deprecation does not mean immediate removal. Deprecated features remain functional for some time to allow developers to transition away from them.

• Possible Removal: Deprecated features may eventually be removed in a future release, although some features remain deprecated for many years before removal (if ever).

5. Removal

Purpose:

The removal stage is the final stage where a deprecated feature, API, or tool is completely removed from the JDK. This step is taken to clean up the language or platform and to reduce maintenance overhead for features that are no longer relevant or have been replaced by better alternatives.

Characteristics:

• No Longer Available: Once a feature is removed, it is no longer available in the JDK, and any code that relies on it will not compile or run.

• Planned and Communicated: The removal of a feature is usually communicated well in advance, giving developers time to refactor or migrate their code.

Examples:

• Features like Thread.stop() and the Java Applet API have been deprecated and eventually removed due to security risks or irrelevance in modern software development.

1. Primitive Types in Patterns, instanceof, and switch

JEP 455 proposes enhancements to Java’s pattern matching capabilities by allowing primitive types in patterns used with instanceof and switch expressions. This is part of Java’s ongoing effort to make pattern matching a more powerful and expressive tool for developers.

What is Pattern Matching in Java?

Pattern matching in Java allows developers to extract values from an object and apply conditional logic based on the structure or type of that object. Initially introduced in JDK 16 with pattern matching for instanceof, this feature simplifies code by eliminating unnecessary casting and providing more readable and concise syntax.

Example of Pattern Matching with instanceof in JDK 16:

Object obj = "Hello, Java!";
if (obj instanceof String s) {
    System.out.println("String value: " + s);
}

In this example, the instanceof pattern checks if obj is a String and, if so, casts it to a variable s that can be used within the scope of the if block. This removes the need for an explicit cast, making the code simpler and less error-prone.

What Does JEP 455 Bring?

JEP 455 extends pattern matching capabilities by allowing primitive types in patterns for instanceof and switch expressions. This means you can now use pattern matching directly with primitive types like int, long, double, etc., which was not possible in previous Java versions.

Key Features of JEP 455:

1. Support for Primitive Type Patterns in instanceof:

• With JEP 455, instanceof can be used to check if an object can be converted to a primitive type and extract that value directly.

Example:

Object obj = 42;
if (obj instanceof Integer i) {
    System.out.println("Integer value: " + i);
}

1. Support for Primitive Type Patterns in switch:

• This enhancement allows switch statements to match patterns based on primitive types, enhancing the readability and flexibility of the code.

Example:

Object obj = 42;
switch (obj) {
    case Integer i -> System.out.println("Integer value: " + i);
    case Long l -> System.out.println("Long value: " + l);
    case Double d -> System.out.println("Double value: " + d);
    default -> System.out.println("Unknown type");
}

The switch expression above matches the obj variable against different primitive type patterns (Integer, Long, Double). This eliminates the need for nested if-else statements and makes the code more concise and easier to maintain.

For more information about primitive types in pattern, read more JEP 455: Primitive Types in Patterns, instanceof, and switch.

2. Flexible Constructor Bodies

Flexible Constructor Bodies refer to a Java feature enhancement proposal aimed at improving the way constructors are written and used in Java. This concept allows constructors to have more flexible syntax and semantics, enhancing readability and reducing boilerplate code.

The idea is to make constructors more intuitive by allowing developers to use more advanced initialization logic directly within the constructor body. Here’s a deeper look into what flexible constructor bodies mean and how they can impact Java development:

1. Traditional Constructors in Java

In Java, constructors are special methods that are called when an object is instantiated. A constructor initializes the newly created object and sets up initial states. Traditionally, constructors have strict rules about how they operate:

• They must have the same name as the class.

• They cannot return any value (not even void).

• They initialize the object immediately, without much flexibility for conditional logic or complex initialization.

Example of a Traditional Constructor:

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        this.name = name;
        this.age = age;
    }
}

While this works well for simple cases, more complex initialization logic can make constructors cumbersome and difficult to read.

2. What are Flexible Constructor Bodies?

The idea behind flexible constructor bodies is to provide more freedom in how constructors can be written and used, particularly in more complex scenarios:

• Use of this() and super() calls anywhere within the constructor body: Traditionally, calls to this() (to call another constructor within the same class) or super() (to call a superclass constructor) must be the first statement in the constructor body. Flexible constructor bodies would allow these calls to be made conditionally or anywhere within the constructor body.

• More complex initialization logic: Developers can write more expressive and complex initialization logic directly in the constructor body without needing to call private methods or use static factory methods.

• Deferred Initialization: Allowing deferred initialization can be beneficial in cases where the constructor logic depends on certain conditions or needs to be delayed until certain resources are available.

3. Example of Flexible Constructor Body (Hypothetical Syntax):

Here is a conceptual example illustrating what a flexible constructor body might look like with more advanced syntax:

public class Person {
    private String name;
    private int age;

    public Person(String name, int age) {
        if (name == null || name.isEmpty()) {
            throw new IllegalArgumentException("Name cannot be null or empty");
        }

        this.name = name;

        if (age < 0) {
            super();  // Hypothetical usage: Calling a parent constructor conditionally
            this.age = 0;
        } else {
            this.age = age;
        }

        // Hypothetical: Complex initialization could continue here
        initializeAdditionalProperties();
    }

    private void initializeAdditionalProperties() {
        // Additional complex initialization logic
    }
}

4. Impact on Java Development

While Java has not fully embraced flexible constructor bodies as a standard feature (as of the latest JDK versions), the idea has been discussed in the community as a way to make Java more modern and expressive. Adopting this feature would align Java more closely with other modern programming languages that already offer more flexible initialization patterns.

The introduction of flexible constructor bodies would represent a significant change to Java’s object-oriented programming model, potentially leading to more powerful and succinct code but also requiring careful consideration of backward compatibility and consistency within the language’s design philosophy.

For more information about flexible constructor body, read more JEP 482: Flexible Constructor Bodies.

3. Class-File API

JEP 466, titled “Class-File API”, proposes a new Java API for reading and writing Java class files. The primary goal of this enhancement is to provide a better, more robust, and flexible mechanism for interacting with Java class files directly within the Java programming language. This proposal is part of JDK 24 and aims to simplify and modernize how developers and tools interact with .class files.

Overview of the Class-File API

Java class files are the compiled bytecode representation of Java source files (.java). These class files contain information about the class, including methods, fields, bytecode instructions, constant pool entries, and more. Traditionally, manipulating or reading these class files has required external libraries (such as ASM or BCEL) or complex manual parsing.

JEP 466 introduces a new API to the Java Development Kit (JDK) that allows developers to read, modify, and write Java class files directly from Java code without relying on external libraries. This API is designed to be easy to use, highly reliable, and closely aligned with the Java Virtual Machine (JVM) specifications.

Goals of JEP 466

1. Ease of Use: Provide a straightforward API for reading and writing Java class files. This API should simplify the tasks that currently require complex or verbose code when using low-level libraries.

2. Alignment with JVM Specifications: The API should closely match the Java Virtual Machine Specification, ensuring correctness and compatibility with future changes in the JVM.

3. Reliability and Safety: The API should prevent common errors and unsafe practices when working with class files, such as incorrect bytecode manipulation or invalid constant pool references.

4. Support for Tools and Frameworks: Provide a standard, efficient mechanism for tools (like debuggers, IDEs, and profilers) and frameworks that need to interact with class files.

5. Performance: The API should be performant, allowing for efficient parsing and writing of class files, especially when dealing with large numbers of files or complex modifications.

Key Features of the Class-File API

The new Class-File API proposed by JEP 466 provides several important features that make working with Java class files easier and more intuitive:

1. Reading Class Files:

• The API allows reading of class files into a tree-like structure that represents all the components of a class file, such as the constant pool, methods, fields, attributes, and bytecode instructions.

Example:

ClassFile classFile = ClassFile.read(inputStream);
classFile.methods().forEach(method -> System.out.println(method.name()));

This snippet reads a class file from an input stream and prints out the names of all the methods defined in the class.

1. Modifying Class Files:

• The API enables modification of class file components. For example, you can add or remove methods, modify bytecode instructions, or update constant pool entries.

Example:

ClassFile classFile = ClassFile.read(inputStream);
Method method = classFile.methods().stream()
                        .filter(m -> m.name().equals("oldMethodName"))
                        .findFirst()
                        .orElseThrow();
method.setName("newMethodName");

This example reads a class file, finds a method by its name, and changes its name to a new value.

1. Writing Class Files:

• Once modifications are made, the API provides methods to write the modified class structure back to a class file format.

Example:

classFile.write(outputStream);

After modifying the class file, this code writes the updated version back to an output stream.

1. Support for JVM Attributes and Bytecode Instructions:

• The API provides detailed support for JVM-specific constructs like attributes (e.g., LineNumberTable, StackMapTable) and bytecode instructions, making it possible to perform sophisticated bytecode analysis or manipulation.

1. Safety Features:

• The API includes safety checks and validations to prevent illegal modifications, ensuring that the resulting class files conform to the JVM specification and do not produce runtime errors.

1. Extensibility:

• The API is designed to be extensible, allowing future updates to accommodate changes in the JVM specification or new features in future versions of Java.

For more details on JEP 466, you can visit the JEP 466 documentation.

4. Module Import Declarations

JEP 476, titled “Module Import Declarations,” is a proposal to enhance the Java programming language with a new syntax and mechanism for module import declarations. This JEP aims to improve how Java modules interact and depend on each other by providing more explicit control over module dependencies within the code. The key motivation is to make module dependencies clearer and safer by being more declarative in code.

Key Points of JEP 476

1. Current Module System and Its Limitations:

• Java introduced the module system in Java 9 through Project Jigsaw, which allows developers to organize code into modules.

• Currently, module dependencies are declared in the module-info.java file using requires clauses. This mechanism, however, is somewhat separated from the actual code using those modules, which can lead to potential discrepancies and makes it less visible at the usage site.

1. Proposal for Module Import Declarations:

• JEP 476 proposes a new language construct to declare module dependencies directly at the usage site in Java source files.

• This new construct is akin to traditional import statements but applies to modules rather than classes or packages. The proposed syntax is:

import module <module-name>;

• For example, to import a module named com.example.utils, one would write:

import module com.example.utils;

Example 1: Basic Module Import

Consider a Java class that needs to use a utility module named com.example.utils. With JEP 476, you could explicitly declare this dependency at the top of your Java source file:

import module com.example.utils;

public class MyApplication {
    public static void main(String[] args) {
        // Use a utility class from the com.example.utils module
        UtilityClass.doSomething();
    }
}

Explanation:

• The import module com.example.utils; statement makes it explicit that this class depends on the com.example.utils module. This makes the dependency visible directly in the source code rather than just in the module-info.java file.

Example 2: Multiple Module Imports

Suppose you have a class that depends on multiple modules, such as a logging module (com.example.logging) and a database module (com.example.database).

import module com.example.logging;
import module com.example.database;

public class DataService {
    public void performOperation() {
        // Log an operation
        Logger.log("Operation started");

        // Use a class from the database module
        DatabaseConnection connection = DatabaseManager.getConnection();
        connection.executeQuery("SELECT * FROM table");

        // Log the completion
        Logger.log("Operation completed");
    }
}

Explanation:

• The import module declarations clearly indicate which modules this class relies on (com.example.logging and com.example.database). This makes it easier for other developers (or tools) to understand which modules are necessary for this class to function.

Example 3: Conditional Module Imports

Imagine a situation where a module is only needed under certain conditions (e.g., a test module only used in testing). With the module import declaration, you can explicitly import a module for a specific class used in testing:

import module com.example.testing;

public class MyApplicationTest {
    public static void main(String[] args) {
        // Use testing utilities
        TestUtility.runTests();
    }
}

Explanation:

• The import module com.example.testing; statement makes it clear that this class (MyApplicationTest) relies on the com.example.testing module, which might only be available in the test runtime environment. This helps in distinguishing dependencies required for different environments.

Example 4: Handling Transitive Dependencies

Consider a scenario where a module com.example.app relies on another module com.example.core, which in turn depends on com.example.utils. In the current module system, this transitive dependency is handled via requires transitive in the module-info.java file. With the new import declarations, you can control this more explicitly:

In com.example.core:

// module-info.java
module com.example.core {
    requires module com.example.utils;
}

// CoreFunctionality.java
import module com.example.utils;

public class CoreFunctionality {
    public void coreMethod() {
        UtilityClass.utilityMethod();
    }
}

In com.example.app:

// Application.java
import module com.example.core;

public class Application {
    public void appMethod() {
        CoreFunctionality cf = new CoreFunctionality();
        cf.coreMethod();
    }
}

Explanation:

• com.example.core explicitly imports the com.example.utils module for its internal use, and com.example.app only imports com.example.core. This makes it clear that Application doesn’t directly depend on com.example.utils; it only depends on com.example.core, which in turn handles its own dependencies.

For more details on JEP 476, you can visit the JEP 476 documentation.

5. Structured Concurrency

JEP 480: Structured Concurrency is a proposal aimed at enhancing the Java concurrency model by introducing structured concurrency APIs. Structured concurrency treats multiple tasks running in parallel as a single unit of work, thereby simplifying multi-threaded programming and improving observability, reliability, and error handling.

Motivation for JEP 480

Java has traditionally provided powerful concurrency utilities (like Thread, ExecutorService, CompletableFuture, etc.), but managing multiple concurrent tasks can be error-prone. Key challenges include:

• Manual thread management: The developer must manually manage thread creation, coordination, and termination, which can lead to resource leaks, orphaned tasks, and unpredictable states.

• Complex error handling: Handling exceptions across multiple threads is complicated; a failure in one thread might not propagate properly, leading to inconsistent states.

• Poor observability and maintainability: It’s often difficult to understand and debug concurrent code, especially when the logic spans multiple methods or classes.

Structured concurrency addresses these challenges by providing a framework where multiple concurrent tasks are treated as a single unit, ensuring better lifecycle management and error handling.

Key Concepts of JEP 480

1. Structured Concurrency:

• Ensures that tasks are initiated, executed, and completed together within a well-defined scope. If one task fails, the entire structure is aborted, and resources are cleaned up automatically.

1. Scopes and Lifecycles:

• Tasks are grouped into a scope. A scope is a context within which tasks run concurrently. When the scope exits (either by completing normally or due to an exception), all tasks are automatically awaited, and resources are cleaned up.

1. Error Propagation and Handling:

• Errors in any task within a structured scope are propagated back to the initiating context, allowing consistent and centralized error handling.

Structured Concurrency with Examples

To illustrate how JEP 480’s structured concurrency can simplify concurrent programming in Java, let’s walk through a few examples:

Example 1: Simple Concurrent Tasks

Suppose we have two tasks: fetching data from a database and retrieving data from a remote API. We want both tasks to run concurrently, and then combine the results.

try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    // Start concurrent tasks within the scope
    Future<String> dbFuture = scope.fork(() -> fetchDataFromDatabase());
    Future<String> apiFuture = scope.fork(() -> fetchDataFromApi());

    // Join the tasks and combine results
    scope.join();  // Wait for both tasks to complete
    scope.throwIfFailed();  // Propagate exceptions if any task failed

    // Retrieve results from the futures
    String dbResult = dbFuture.resultNow();
    String apiResult = apiFuture.resultNow();

    // Process combined results
    System.out.println("Combined Result: " + dbResult + apiResult);
}

Explanation:

• Scope: The StructuredTaskScope.ShutdownOnFailure() creates a new structured scope where tasks are executed. If any task fails, all tasks are canceled.

• Forking Tasks: scope.fork() starts a new concurrent task within the scope.

• Joining and Error Handling: scope.join() waits for all tasks to complete, and scope.throwIfFailed() ensures that if any task failed, an exception is thrown.

• Result Retrieval: Results are fetched using Future.resultNow() after all tasks are successfully completed.

Example 2: Handling Task Failures

Consider a scenario where one of the tasks might fail, and we want to ensure all resources are cleaned up correctly.

try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    Future<String> task1 = scope.fork(() -> performTask1());
    Future<String> task2 = scope.fork(() -> performTask2()); // This task might fail

    scope.join();  // Wait for both tasks to complete
    scope.throwIfFailed();  // If task2 fails, an exception is thrown here

    String result1 = task1.resultNow();
    String result2 = task2.resultNow();

    System.out.println("Task 1 Result: " + result1);
    System.out.println("Task 2 Result: " + result2);
} catch (Exception e) {
    System.err.println("Error occurred: " + e.getMessage());
    // Handle failure case
}

Explanation:

• If performTask2() fails, the scope.throwIfFailed() will throw an exception, and the structured scope ensures that any resources associated with both task1 and task2 are properly cleaned up.

• The catch block handles any exceptions raised due to task failure.

Example 3: Timeout Management

Suppose you want to add a timeout to ensure that all tasks within the scope complete within a certain duration.

try (var scope = new StructuredTaskScope.ShutdownOnFailure()) {
    Future<String> task1 = scope.fork(() -> performTask1());
    Future<String> task2 = scope.fork(() -> performTask2());

    boolean finishedInTime = scope.joinUntil(Instant.now().plusSeconds(10));  // Wait for up to 10 seconds

    if (!finishedInTime) {
        System.err.println("Timeout occurred before tasks completed.");
        return;
    }

    scope.throwIfFailed();

    String result1 = task1.resultNow();
    String result2 = task2.resultNow();

    System.out.println("Results: " + result1 + ", " + result2);
} catch (Exception e) {
    System.err.println("Error: " + e.getMessage());
}

Explanation:

• scope.joinUntil(Instant.now().plusSeconds(10)) waits up to 10 seconds for all tasks to complete. If they don’t complete within the specified time, it returns false.

• This timeout mechanism ensures that long-running tasks don’t block the main thread indefinitely.

6. ZGC: Generational Mode by Default

JEP 474: ZGC: Generational Mode by Default is a proposal to enhance the Z Garbage Collector (ZGC) in the Java Virtual Machine (JVM) by enabling generational garbage collection mode by default.

Background: The Z Garbage Collector (ZGC)

The Z Garbage Collector (ZGC) is a scalable, low-latency garbage collector introduced in JDK 11. It was designed to handle large heaps (multi-terabyte sizes) with minimal pause times, often in the range of just a few milliseconds. ZGC achieves this by performing most of its work concurrently with the execution of application threads, minimizing the impact of garbage collection on application performance.

Initially, ZGC was a non-generational collector, meaning it didn’t distinguish between young and old generations of objects. All objects were treated equally, regardless of their age, which simplified the design but missed opportunities to optimize based on object lifespan.

Generational Garbage Collection

Generational garbage collection is based on the observation that most objects in Java applications are short-lived. It divides the heap into two or more regions:

• Young Generation: This is where new objects are allocated. Most objects die young, so frequent, fast garbage collections occur here.

• Old Generation: This is where objects that have survived multiple garbage collection cycles are moved. These objects tend to live longer, and garbage collection is less frequent here but more expensive.

By distinguishing between young and old objects, a generational garbage collector can reduce the overhead of collecting short-lived objects and defer the collection of long-lived objects, improving overall performance.

JEP 474: ZGC Generational Mode

JEP 474 proposes to enhance ZGC by making it generational by default. This means:

1. Enable Generational Mode: ZGC will operate in a generational mode, distinguishing between young and old generations of objects.

2. Improve Performance: By adopting a generational approach, ZGC can optimize for the fact that most objects are short-lived, reducing the frequency and duration of garbage collection pauses.

3. Backward Compatibility: The change will be backward compatible, allowing existing applications to benefit from the improved performance without requiring code changes.

Benefits of ZGC Generational Mode

1. Improved Throughput:

• Generational garbage collection is typically more efficient because it focuses on collecting short-lived objects frequently and defers the more expensive collection of long-lived objects.

1. Reduced Latency:

• Even though ZGC is designed to be low-latency, generational collection can further reduce the impact of garbage collection by optimizing the collection of short-lived objects.

1. Better Resource Utilization:

• By allocating new objects in a separate region (young generation), ZGC can more effectively manage memory and CPU resources.

Conclusion

JDK 23 is packed with features that make Java more powerful, flexible, and user-friendly. From improved concurrency models with Virtual Threads to enhanced garbage collection, this release has something to offer every Java developer.

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