Diving into Modern Java: Key Features in Java 25 and the On-Ramp for Beginners

Nikolai, a Java Developer Advocate for Oracle, recently provided insights into the evolving landscape of the Java language, highlighting finalized features in Java 25 and major changes aimed at simplifying the entry point for new developers. The discussion revealed that many in the audience are already running modern versions like Java 17, 21, and even 24, signaling a healthy adoption of recent releases.

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Java 25 Final Features and Recent Updates

The session touched upon a range of features finalized in the latest releases, with a specific focus on Java 25.

Finalized in Java 25

A significant list of features have been finalized in Java 25, including:

• Module Import Simplified

• Main Flexible Constructor Bodies

• Scope Values

• Method Profiling and Easier Command Line Interaction

• JFR Improvements

• Compact Object Headers

The discussion noted that the list of finalized features in Java 24 was also substantial, covering things like Unnamed Patterns for Records, the Foreign Function & Memory API, and Multisource File Execution.

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Module Imports: An Upgrade to Star Imports

A key point of discussion centered on Module Imports, presented as a potential upgrade for developers who currently use star imports (e.g., import com.example.*).

Star Imports vs. Module Imports

While star imports are valued for being succinct and easier to manage manually, they suffer from potential conflicts and can provide an arbitrary slice of an API by importing all public types from a package.

Module Imports (import module module-name;) offer similar benefits:

• They are very succinct.

• They are trivial to manage manually.

• They import the entire public API exported by that module, eliminating the issue of getting an "arbitrary slice" of functionality.

For existing users of star imports, module imports are positioned as a clear, superior alternative that maintains brevity while leveraging the structured nature of the Java Platform Module System (JPMS).

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The Java On-Ramp: Simplified Main and Easier Execution

Perhaps the most significant shift discussed is the effort to create a better on-ramp for new Java developers, moving away from the historically complex setup required to run a simple program.

The Problem for Beginners

Java's mature ecosystem—with its detailed visibility modifiers, complex build tools (Maven/Gradle), and multiple JDK distributions—is excellent for professionals but presents a high barrier to entry for beginners. New learners often struggle with the boilerplate of a traditional Java entry point:

$$\text{public static void main(String[] args)}$$

This standard requires understanding concepts like classes, public scope, static methods, and the argument array (args) before even writing a line of logic. Furthermore, the need to use System.out.println() introduces the confusing static field out inside the System class.

The Solution: Simplified Main

Java 25 finalizes features that allow for simplified main methods. This allows a beginner to write executable code directly within a method body, without the surrounding class wrapper:

Java

void main() {
    // Code runs here directly
    IO.println("Hello, world!");
}

This simplified structure provides several advantages:

1. Concept Reduction: Beginners skip learning about classes, static/public modifiers, and argument arrays immediately.

2. Easier I/O: A new IO class provides simple methods like print, println, and readLine, abstracting away stream handling.

3. Implicit Imports: The simple main method automatically receives an import module java.base;, giving free access to core types like List, BigDecimal, and LocalDate.

4. Direct Execution: The Java launcher can execute this single file directly using java main.java, skipping the explicit compilation step and managing classpath/module path automatically for local files and dependencies on the path.

This approach allows new learners to focus on statements and expressions first, creating a natural progression where concepts like command-line arguments, fields, and external APIs can be introduced gradually.

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Flexible Constructor Bodies and Constructor Chaining

The session also touched upon Flexible Constructor Bodies, which addresses the common practice of constructor chaining to ensure a single source of truth for instance initialization and validation.

The core principle remains that in inheritance, the superclass constructor must be called before the subclass constructor runs any of its own code. This ensures the base object is fully initialized first.

The new flexibility aims to relax the rule that no code can appear before super() or this() in a constructor. While explicit calls to super() or this() must still be the first statement, the rule is being softened to mean no code that executes logic before the initial chaining call is made. This resolves issues where chaining constructors were forced to be perfectly clean, even if the logic before the chain call was harmless.