JDK 25: Supporting Compact Source Files In Javelit

Nov 27, 2025 by Alex Johnson 51 views

Introduction

Java Development Kit (JDK) 25 introduces several new features, including compact source files, which allow for more concise and streamlined code. This article delves into the challenges of supporting these new features in Javelit, a Java development tool, and outlines the necessary steps to ensure compatibility. We'll explore the different ways to define the main method in JDK 25 and how Javelit can adapt to support these variations. By understanding these changes, developers can better leverage the new capabilities of JDK 25 while maintaining compatibility with existing tools and frameworks. This article provides a comprehensive guide to understanding and implementing support for compact source files in Javelit, ensuring that developers can seamlessly transition to the latest Java features.

The Challenge: New Ways to Define the Main Method

With the advent of JDK 25, defining the instance main method has become more flexible, presenting both opportunities and challenges for Java developers. Traditionally, the main method in Java follows a specific signature:

public class MyApp {
    // supported
    public static void main(String[] args)

However, JDK 25 introduces several new ways to define the main method, including:

// new in JDK 25 - NOT SUPPORTED
static void main(String[] args) { }  // not public
static void main() { }               // no args
void main(String[] args) { }         // not static (instance method)
void main() { }                      // minimal

Furthermore, compact source files in JDK 25 allow for an even more concise syntax:

// no class declaration
void main() {
    println(greeting + " depuis Java 25!");
}

This flexibility, while beneficial for code brevity, poses a challenge for tools like Javelit that rely on specific signatures to identify the entry point of a Java application. Currently, Javelit only supports the traditional main method, using the following logic:

final Class<?> mainClass = hierarchicalClassLoader.loadClass(name);
Method main = mainClass.getMethod("main", String[].class);

This logic specifically searches for a static, public method with a String[] argument, which means that the new main method variations introduced in JDK 25 are not currently supported. This limitation necessitates updates to Javelit to ensure compatibility with the latest Java features. The primary task is to modify Javelit's method lookup mechanism to accommodate these new main method signatures, allowing developers to seamlessly use JDK 25's compact source files and other related features. This adaptation will not only enhance Javelit's functionality but also ensure that it remains a relevant tool for modern Java development.

Javelit's Current Limitations

As it stands, Javelit's support for the main method is limited to the traditional public static void main(String[] args) signature. This limitation stems from the specific way Javelit locates the entry point of a Java application. The current implementation, as seen in the FileReloader.java file, uses a method that explicitly searches for a static, public method with a String[] argument. This approach, while straightforward, fails to recognize the new variations introduced in JDK 25. Consequently, developers using JDK 25's compact source files or alternative main method signatures will encounter issues when using Javelit. For instance, code that utilizes the minimal void main() method or the non-public static void main(String[] args) method will not be correctly identified as an executable entry point by Javelit. This lack of support not only restricts the usage of new JDK 25 features but also creates a potential barrier for developers who wish to adopt the latest Java standards while continuing to use Javelit. Addressing this limitation is crucial to ensure that Javelit remains a versatile and up-to-date tool for Java development. The necessary modifications will involve expanding Javelit's method lookup capabilities to include the new main method signatures, thereby providing seamless support for JDK 25 and beyond. This enhancement will enable developers to fully leverage the benefits of compact source files and other modern Java features within the Javelit environment.

Proposed Solutions: PR 1, PR 2, and PR 3

To address the limitations and ensure Javelit's compatibility with JDK 25, a series of Pull Requests (PRs) are proposed. These PRs aim to incrementally enhance Javelit's capabilities, focusing on testing, implementation, and documentation. Let's delve into the specifics of each PR:

PR 1 - CI: Test Matrix for JDK 21 and JDK 25

The first step in ensuring compatibility is to establish a robust testing environment. PR 1 focuses on enhancing Javelit's Continuous Integration (CI) setup by adding a test matrix to GitHub Actions. This matrix will ensure that Javelit is tested against both JDK 21 and JDK 25. By testing against multiple JDK versions, we can identify and address compatibility issues early in the development process. This proactive approach helps maintain the stability and reliability of Javelit across different Java environments. The test matrix will include a range of tests, covering core Javelit functionalities as well as specific features related to JDK 25. This comprehensive testing strategy will provide confidence in Javelit's ability to function correctly with the latest Java releases. Ultimately, PR 1 lays the foundation for future enhancements by providing a reliable mechanism for verifying compatibility and identifying potential issues.

PR 2: Expanding Main Method Support

The core of the solution lies in PR 2, which focuses on modifying Javelit to recognize all kinds of main methods introduced in JDK 25. This involves expanding the method lookup logic to include not only the traditional public static void main(String[] args) but also the new variations such as static void main(String[] args), static void main(), void main(String[] args), and void main(). The approach includes the following steps:

JDK Version Check: Implement a check to determine the JDK version. If the version is 25 or higher, the extended main method search will be activated.
Method Lookup: Modify the method lookup logic to search for all valid main method signatures. This includes methods that are not public, have no arguments, or are instance methods (non-static).
New Test Class: Add a new test class specifically designed to test the new main method variations. This test class will only run if the JDK version is 25 or higher. Each test method within this class will include an assumption check to skip the test if the JDK version is less than 25. This ensures that the tests are only executed in the appropriate environment.
```
Assumptions.assumeFalse(
      [JDK VERSION] < 25,
      "JDK version is %s - skipping JDK 25 tests"
  );
```
Specific Tests: Create individual tests for each new main method signature, as well as a test to verify the Java resolution order when multiple matching methods are present.
- Test for static void main(String[] args)
- Test for static void main()
- Test for void main(String[] args) (instance method)
- Test for void main() (instance method, minimal)
- Test for resolution order:
```
static void main(String[] args)   // not public
static void main()                
void main(String[] args)          // instance method (no static)
void main()                       // instance method minimal
```
Constructor Assumption: If the method is not static, assume that there is a no-arg constructor available in the class. This is a common pattern in Java applications.

PR 3: Documentation Update

The final step is to ensure that the new functionality is properly documented. PR 3 focuses on adding a mention of the JDK 25 support in Javelit's documentation. This includes updating the documentation to reflect the new main method signatures that are supported, as well as any specific instructions or considerations for using Javelit with JDK 25. Clear and comprehensive documentation is essential for users to effectively utilize the new features and understand any potential changes in behavior. The documentation update will be included in the release notes and any relevant user guides or tutorials. By keeping the documentation up-to-date, we ensure that Javelit remains accessible and easy to use for all developers, regardless of their familiarity with the tool or the latest Java features.

Detailed Implementation Plan

To effectively implement the proposed solutions, a detailed plan is crucial. This plan outlines the specific steps involved in each PR, ensuring a systematic approach to enhancing Javelit's compatibility with JDK 25. By breaking down the tasks into manageable components, the implementation process becomes more transparent and easier to track. Let's examine the detailed plan for each PR.

PR 1: CI Enhancements

GitHub Actions Configuration: Modify the existing GitHub Actions workflow to include a test matrix.
JDK Versions: Add JDK 21 and JDK 25 to the test matrix.
Test Suites: Ensure all relevant test suites are executed for each JDK version.
Reporting: Configure the CI to report test results for each JDK version separately.
Verification: Verify that the CI runs successfully for both JDK 21 and JDK 25.

PR 2: Expanding Main Method Support

JDK Version Detection: Implement a utility method to detect the JDK version at runtime.
Conditional Method Lookup: Modify the FileReloader.java to use the extended method lookup logic if the JDK version is 25 or higher.
Method Search: Implement the logic to search for main methods with the following signatures:
- static void main(String[] args)
- static void main()
- void main(String[] args)
- void main()
Test Class Creation: Create a new test class named JDK25MainMethodTest.
Test Method Assumptions: Add the Assumptions.assumeFalse check to each test method in JDK25MainMethodTest.
Specific Test Cases: Implement test cases for each main method signature, ensuring they are correctly identified and executed.
Resolution Order Test: Implement a test case to verify the Java resolution order for multiple matching main methods.
No-Arg Constructor Assumption: Ensure that the code assumes a no-arg constructor if a non-static main method is found.
Code Review: Conduct a thorough code review to ensure correctness and adherence to coding standards.

PR 3: Documentation Update

Identify Documentation Sections: Determine the relevant sections in Javelit's documentation that need to be updated.
Update Release Notes: Add a section in the release notes detailing the JDK 25 support.
User Guide Updates: Update the user guide to include information about the new main method signatures and how they are supported in Javelit.
Example Code: Provide example code snippets demonstrating the use of the new main method signatures.
Documentation Review: Review the updated documentation for clarity and completeness.
Publish Updates: Publish the updated documentation on Javelit's website and any other relevant platforms.

By following this detailed implementation plan, the process of enhancing Javelit's compatibility with JDK 25 can be managed effectively, ensuring that all necessary steps are taken to deliver a robust and well-documented solution.

Conclusion

Supporting JDK 25's compact source files and new main method signatures in Javelit is a crucial step towards ensuring the tool remains relevant and adaptable to the evolving Java ecosystem. The proposed solutions, outlined in PR 1, PR 2, and PR 3, provide a comprehensive approach to addressing the challenges and limitations posed by the new JDK features. By implementing these changes, Javelit will be able to seamlessly handle the various ways of defining the main method, including the minimalistic syntax offered by compact source files. This not only enhances Javelit's functionality but also ensures that developers can fully leverage the benefits of JDK 25 while using their preferred development tools. The detailed implementation plan for each PR ensures a systematic and thorough approach, covering testing, code modifications, and documentation updates. This holistic strategy guarantees a smooth transition and a reliable outcome. Ultimately, the effort to support JDK 25 in Javelit underscores the importance of continuous adaptation and improvement in software development, ensuring that tools and frameworks remain aligned with the latest technological advancements. By embracing these changes, Javelit continues to empower developers to create modern, efficient, and compatible Java applications. For more information on Java development and best practices, visit the Oracle Java Documentation.