Java 24: Unlocking Enhanced Performance and Modern Development Capabilities

Java 24 represents a significant milestone in the evolution of the Java platform, bringing together 24 carefully crafted JDK Enhancement Proposals (JEPs) that enhance performance, security, and developer productivity. Let’s explore the major features and their practical implications.

Performance Optimizations

Java 24 introduces two experimental features designed to boost application performance:

Generational Shenandoah Garbage Collector (JEP 404)

The Generational Shenandoah GC represents a significant evolution in Java’s garbage collection strategy, offering improved performance characteristics while maintaining compatibility with existing applications.
Technical Implementation:


<span>// Traditional Shenandoah GC configuration</span>
<span>-</span><span>XX:</span><span>+</span><span>UseShenandoahGC</span>
<span>// New Generational Shenandoah configuration</span>
<span>-</span><span>XX:</span><span>+</span><span>UseShenandoahGC</span> <span>-</span><span>XX:</span><span>+</span><span>ShenandoahGenerational</span>
<span>// Traditional Shenandoah GC configuration</span>
<span>-</span><span>XX:</span><span>+</span><span>UseShenandoahGC</span>
<span>// New Generational Shenandoah configuration</span>
<span>-</span><span>XX:</span><span>+</span><span>UseShenandoahGC</span> <span>-</span><span>XX:</span><span>+</span><span>ShenandoahGenerational</span>
// Traditional Shenandoah GC configuration
-XX:+UseShenandoahGC
// New Generational Shenandoah configuration
-XX:+UseShenandoahGC -XX:+ShenandoahGenerational

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Generation-Based Collection

Objects are grouped by lifetime (young vs old)
Young objects are collected more frequently
Reduces pause times for young generation collections
Improves overall application responsiveness

Memory Management Efficiency

Better utilization of heap space
Reduced memory fragmentation
More predictable garbage collection patterns
Improved cache efficiency

Comparison with Previous Implementation:

Aspect	Traditional Shenandoah	Generational Shenandoah
Collection Strategy	Single-generation approach	Generation-based collection
Pause Times	Variable, dependent on heap size	More predictable, shorter for young generation
Memory Usage	Single heap space	Separated young/old generations
Collection Frequency	Uniform across all objects	Higher for young generation, lower for old
Compatibility	Standalone mode	Maintains compatibility with non generational mode

Compact Object Headers (JEP 450)

The Compact Object Headers feature represents a fundamental change in how Java objects are structured in memory, inspired by Project Lilliput’s goals of reducing memory overhead.

Technical Implementation:


<span>// Enable compact headers (experimental)</span>
<span>-</span><span>XX:</span><span>+</span><span>UseCompactObjectHeaders</span>
<span>// Example object structure comparison</span>
<span>class</span> <span>TraditionalObject</span> <span>{</span>
    <span>// 96-128 bits header</span>
    <span>// Mark word (64 bits)</span>
    <span>// Class pointer (32-64 bits)</span>
    <span>// Array length (for arrays)</span>
    <span>// Hash code (32 bits)</span>
    <span>// GC age (4 bits)</span>
    <span>// Other metadata</span>
<span>}</span>
<span>class</span> <span>CompactObject</span> <span>{</span>
    <span>// 64 bits header</span>
    <span>// Mark word (32 bits)</span>
    <span>// Class pointer (32 bits)</span>
    <span>// Optional fields stored separately</span>
<span>}</span>
<span>// Enable compact headers (experimental)</span>
<span>-</span><span>XX:</span><span>+</span><span>UseCompactObjectHeaders</span>
<span>// Example object structure comparison</span>
<span>class</span> <span>TraditionalObject</span> <span>{</span>
    <span>// 96-128 bits header</span>
    <span>// Mark word (64 bits)</span>
    <span>// Class pointer (32-64 bits)</span>
    <span>// Array length (for arrays)</span>
    <span>// Hash code (32 bits)</span>
    <span>// GC age (4 bits)</span>
    <span>// Other metadata</span>
<span>}</span>
<span>class</span> <span>CompactObject</span> <span>{</span>
    <span>// 64 bits header</span>
    <span>// Mark word (32 bits)</span>
    <span>// Class pointer (32 bits)</span>
    <span>// Optional fields stored separately</span>
<span>}</span>
// Enable compact headers (experimental)
-XX:+UseCompactObjectHeaders
// Example object structure comparison
class TraditionalObject {
    // 96-128 bits header
    // Mark word (64 bits)
    // Class pointer (32-64 bits)
    // Array length (for arrays)
    // Hash code (32 bits)
    // GC age (4 bits)
    // Other metadata
}
class CompactObject {
    // 64 bits header
    // Mark word (32 bits)
    // Class pointer (32 bits)
    // Optional fields stored separately
}

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Memory Efficiency

Reduces object header size by 33-50%
Significant memory savings in object-heavy applications
Particularly beneficial for microservices and cloud deployments
Enables more objects to fit in CPU cache lines

Performance Benefits

Improved cache utilization
Reduced memory bandwidth usage
Faster object allocation and garbage collection
Better scaling in multi-threaded applications

Comparison with Previous Implementation:

Aspect	Traditional Headers	Compact Headers
Header Size	96-128 bits	64 bits
Metadata Storage	All in header	Optional fields stored separately
Cache Efficiency	Lower due to larger size	Higher due to smaller size
Memory Overhead	Higher per object	Lower per object
Status	Production ready	Experimental

Security Enhancements

Java 24 strengthens security with quantum-resistant cryptography:


<span>// Example of Key Derivation Function API (JEP 478)</span>
<span>KeyDerivation</span> <span>keyDerivation</span> <span>=</span> <span>KeyDerivation</span><span>.</span><span>getInstance</span><span>(</span><span>"PBKDF2WithHmacSHA256"</span><span>);</span>
<span>KeySpec</span> <span>keySpec</span> <span>=</span> <span>keyDerivation</span><span>.</span><span>deriveKey</span><span>(</span>
    <span>new</span> <span>PBEParameterSpec</span><span>(</span><span>salt</span><span>,</span> <span>iterationCount</span><span>),</span>
    <span>KeyType</span><span>.</span><span>AES</span>
<span>);</span>
<span>// Example of Key Derivation Function API (JEP 478)</span>
<span>KeyDerivation</span> <span>keyDerivation</span> <span>=</span> <span>KeyDerivation</span><span>.</span><span>getInstance</span><span>(</span><span>"PBKDF2WithHmacSHA256"</span><span>);</span>
<span>KeySpec</span> <span>keySpec</span> <span>=</span> <span>keyDerivation</span><span>.</span><span>deriveKey</span><span>(</span>
    <span>new</span> <span>PBEParameterSpec</span><span>(</span><span>salt</span><span>,</span> <span>iterationCount</span><span>),</span>
    <span>KeyType</span><span>.</span><span>AES</span>
<span>);</span>
// Example of Key Derivation Function API (JEP 478)
KeyDerivation keyDerivation = KeyDerivation.getInstance("PBKDF2WithHmacSHA256");
KeySpec keySpec = keyDerivation.deriveKey(
    new PBEParameterSpec(salt, iterationCount),
    KeyType.AES
);

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This release implements three significant security features:

Key Derivation Function API
Quantum-Resistant Module-Lattice-Based Key Encapsulation Mechanism (ML-KEM)
Quantum-Resistant Module-Lattice-Based Digital Signature Algorithm (ML-DSA)

Developer Experience Improvements

The release significantly enhances developer productivity with simpler syntax:


<span>// Traditional Hello World</span>
<span>public</span> <span>class</span> <span>HelloWorld</span> <span>{</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>System</span><span>.</span><span>out</span><span>.</span><span>println</span><span>(</span><span>"Hello World!"</span><span>);</span>
    <span>}</span>
<span>}</span>
<span>// New Simplified Version (JEP 495)</span>
<span>void</span> <span>main</span><span>()</span> <span>{</span>
    <span>println</span><span>(</span><span>"Hello World!"</span><span>);</span>
<span>}</span>
<span>// Traditional Hello World</span>
<span>public</span> <span>class</span> <span>HelloWorld</span> <span>{</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>System</span><span>.</span><span>out</span><span>.</span><span>println</span><span>(</span><span>"Hello World!"</span><span>);</span>
    <span>}</span>
<span>}</span>
<span>// New Simplified Version (JEP 495)</span>
<span>void</span> <span>main</span><span>()</span> <span>{</span>
    <span>println</span><span>(</span><span>"Hello World!"</span><span>);</span>
<span>}</span>
// Traditional Hello World
public class HelloWorld {
    public static void main(String[] args) {
        System.out.println("Hello World!");
    }
}
// New Simplified Version (JEP 495)
void main() {
    println("Hello World!");
}

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Key improvements include:

Simple source files and instance main methods
Reduced complexity for beginners (only 1 principle vs 32 previously)
Introduction of Learn.java, a dedicated educational resource

Modernization Features

Several important modernization efforts are part of this release:
Stream Gatherers (JEP 485)


<span>List</span><span><</span><span>Employee</span><span>></span> <span>employees</span> <span>=</span> <span>List</span><span>.</span><span>of</span><span>(</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"John"</span><span>,</span> <span>30000</span><span>,</span> <span>"Engineering"</span><span>),</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"Jane"</span><span>,</span> <span>35000</span><span>,</span> <span>"Marketing"</span><span>),</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"Bob"</span><span>,</span> <span>28000</span><span>,</span> <span>"Engineering"</span><span>)</span>
<span>);</span>
<span>try</span> <span>(</span><span>var</span> <span>gatherer</span> <span>=</span> <span>Stream</span><span>.</span><span>gatherer</span><span>(</span>
    <span>// Collect engineers</span>
    <span>Collectors</span><span>.</span><span>filtering</span><span>(</span><span>e</span> <span>-></span> 
    <span>e</span><span>.</span><span>getDepartment</span><span>().</span><span>equals</span><span>(</span><span>"Engineering"</span><span>),</span> <span>Collectors</span><span>.</span><span>toList</span><span>()),</span>
    <span>// Group by department</span>
    <span>Collectors</span><span>.</span><span>groupingBy</span><span>(</span><span>Employee:</span><span>:</span><span>getDepartment</span><span>),</span>
    <span>// Calculate total salary</span>
    <span>Collectors</span><span>.</span><span>summingInt</span><span>(</span><span>Employee:</span><span>:</span><span>getSalary</span><span>)</span>
<span>))</span> <span>{</span>
    <span>var</span> <span>result</span> <span>=</span> <span>employees</span><span>.</span><span>stream</span><span>().</span><span>collect</span><span>(</span><span>gatherer</span><span>);</span>
    <span>List</span><span><</span><span>Employee</span><span>></span> <span>engineers</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>0</span><span>);</span>
    <span>Map</span><span><</span><span>String</span><span>,</span> <span>List</span><span><</span><span>Employee</span><span>>></span> <span>byDepartment</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>1</span><span>);</span>
    <span>int</span> <span>totalSalary</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>2</span><span>);</span>
<span>}</span>
<span>List</span><span><</span><span>Employee</span><span>></span> <span>employees</span> <span>=</span> <span>List</span><span>.</span><span>of</span><span>(</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"John"</span><span>,</span> <span>30000</span><span>,</span> <span>"Engineering"</span><span>),</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"Jane"</span><span>,</span> <span>35000</span><span>,</span> <span>"Marketing"</span><span>),</span>
    <span>new</span> <span>Employee</span><span>(</span><span>"Bob"</span><span>,</span> <span>28000</span><span>,</span> <span>"Engineering"</span><span>)</span>
<span>);</span>
<span>try</span> <span>(</span><span>var</span> <span>gatherer</span> <span>=</span> <span>Stream</span><span>.</span><span>gatherer</span><span>(</span>
    <span>// Collect engineers</span>
    <span>Collectors</span><span>.</span><span>filtering</span><span>(</span><span>e</span> <span>-></span> 
    <span>e</span><span>.</span><span>getDepartment</span><span>().</span><span>equals</span><span>(</span><span>"Engineering"</span><span>),</span> <span>Collectors</span><span>.</span><span>toList</span><span>()),</span>
    <span>// Group by department</span>
    <span>Collectors</span><span>.</span><span>groupingBy</span><span>(</span><span>Employee:</span><span>:</span><span>getDepartment</span><span>),</span>
    <span>// Calculate total salary</span>
    <span>Collectors</span><span>.</span><span>summingInt</span><span>(</span><span>Employee:</span><span>:</span><span>getSalary</span><span>)</span>
<span>))</span> <span>{</span>
    <span>var</span> <span>result</span> <span>=</span> <span>employees</span><span>.</span><span>stream</span><span>().</span><span>collect</span><span>(</span><span>gatherer</span><span>);</span>
    <span>List</span><span><</span><span>Employee</span><span>></span> <span>engineers</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>0</span><span>);</span>
    <span>Map</span><span><</span><span>String</span><span>,</span> <span>List</span><span><</span><span>Employee</span><span>>></span> <span>byDepartment</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>1</span><span>);</span>
    <span>int</span> <span>totalSalary</span> <span>=</span> <span>result</span><span>.</span><span>get</span><span>(</span><span>2</span><span>);</span>
<span>}</span>
List<Employee> employees = List.of(
    new Employee("John", 30000, "Engineering"),
    new Employee("Jane", 35000, "Marketing"),
    new Employee("Bob", 28000, "Engineering")
);
try (var gatherer = Stream.gatherer(
    // Collect engineers
    Collectors.filtering(e -> 
    e.getDepartment().equals("Engineering"), Collectors.toList()),
    // Group by department
    Collectors.groupingBy(Employee::getDepartment),
    // Calculate total salary
    Collectors.summingInt(Employee::getSalary)
)) {
    var result = employees.stream().collect(gatherer);
    List<Employee> engineers = result.get(0);
    Map<String, List<Employee>> byDepartment = result.get(1);
    int totalSalary = result.get(2);
}

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This example demonstrates how Stream Gatherers allow multiple collection operations in a single pass through the data, improving efficiency and reducing boilerplate code.
Ahead-of-Time Class Loading & Linking (JEP 483)


<span>// Traditional loading</span>
<span>public</span> <span>class</span> <span>Application</span> <span>{</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>// Classes are loaded and linked during runtime</span>
        <span>Database</span> <span>db</span> <span>=</span> <span>new</span> <span>Database</span><span>();</span>
        <span>Cache</span> <span>cache</span> <span>=</span> <span>new</span> <span>Cache</span><span>();</span>
    <span>}</span>
<span>}</span>
<span>// Modern approach with AOT loading</span>
<span>public</span> <span>class</span> <span>Application</span> <span>{</span>
    <span>static</span> <span>{</span>
        <span>System</span><span>.</span><span>loadPredefinedClass</span><span>(</span><span>Database</span><span>.</span><span>class</span><span>);</span>
        <span>System</span><span>.</span><span>loadPredefinedClass</span><span>(</span><span>Cache</span><span>.</span><span>class</span><span>);</span>
    <span>}</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>// Instant startup for predefined classes</span>
        <span>Database</span> <span>db</span> <span>=</span> <span>new</span> <span>Database</span><span>();</span>
        <span>Cache</span> <span>cache</span> <span>=</span> <span>new</span> <span>Cache</span><span>();</span>
    <span>}</span>
<span>}</span>
<span>// Traditional loading</span>
<span>public</span> <span>class</span> <span>Application</span> <span>{</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>// Classes are loaded and linked during runtime</span>
        <span>Database</span> <span>db</span> <span>=</span> <span>new</span> <span>Database</span><span>();</span>
        <span>Cache</span> <span>cache</span> <span>=</span> <span>new</span> <span>Cache</span><span>();</span>
    <span>}</span>
<span>}</span>
<span>// Modern approach with AOT loading</span>
<span>public</span> <span>class</span> <span>Application</span> <span>{</span>
    <span>static</span> <span>{</span>
        <span>System</span><span>.</span><span>loadPredefinedClass</span><span>(</span><span>Database</span><span>.</span><span>class</span><span>);</span>
        <span>System</span><span>.</span><span>loadPredefinedClass</span><span>(</span><span>Cache</span><span>.</span><span>class</span><span>);</span>
    <span>}</span>
    <span>public</span> <span>static</span> <span>void</span> <span>main</span><span>(</span><span>String</span><span>[]</span> <span>args</span><span>)</span> <span>{</span>
        <span>// Instant startup for predefined classes</span>
        <span>Database</span> <span>db</span> <span>=</span> <span>new</span> <span>Database</span><span>();</span>
        <span>Cache</span> <span>cache</span> <span>=</span> <span>new</span> <span>Cache</span><span>();</span>
    <span>}</span>
<span>}</span>
// Traditional loading
public class Application {
    public static void main(String[] args) {
        // Classes are loaded and linked during runtime
        Database db = new Database();
        Cache cache = new Cache();
    }
}
// Modern approach with AOT loading
public class Application {
    static {
        System.loadPredefinedClass(Database.class);
        System.loadPredefinedClass(Cache.class);
    }
    public static void main(String[] args) {
        // Instant startup for predefined classes
        Database db = new Database();
        Cache cache = new Cache();
    }
}

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This feature works by monitoring application usage patterns during development and storing optimized class representations for future runs.
Vector API (JEP 489)


<span>// Traditional array processing</span>
<span>double</span><span>[]</span> <span>prices</span> <span>=</span> <span>{</span><span>100.0</span><span>,</span> <span>200.0</span><span>,</span> <span>300.0</span><span>,</span> <span>400.0</span><span>};</span>
<span>double</span> <span>discountFactor</span> <span>=</span> <span>0.9</span><span>;</span>
<span>double</span><span>[]</span> <span>discountedPrices</span> <span>=</span> <span>new</span> <span>double</span><span>[</span><span>prices</span><span>.</span><span>length</span><span>];</span>
<span>for</span> <span>(</span><span>int</span> <span>i</span> <span>=</span> <span>0</span><span>;</span> <span>i</span> <span><</span> <span>prices</span><span>.</span><span>length</span><span>;</span> <span>i</span><span>++)</span> <span>{</span>
    <span>discountedPrices</span><span>[</span><span>i</span><span>]</span> <span>=</span> <span>prices</span><span>[</span><span>i</span><span>]</span> <span>*</span> <span>discountFactor</span><span>;</span>
<span>}</span>
<span>// Vector API approach</span>
<span>try</span> <span>(</span><span>var</span> <span>vector</span> <span>=</span> <span>DoubleVector</span><span>.</span><span>fromArray</span><span>(</span><span>prices</span><span>,</span> <span>0</span><span>))</span> <span>{</span>
    <span>var</span> <span>discounted</span> <span>=</span> <span>vector</span><span>.</span><span>mul</span><span>(</span><span>discountFactor</span><span>);</span>
    <span>discounted</span><span>.</span><span>intoArray</span><span>(</span><span>prices</span><span>,</span> <span>0</span><span>);</span>
<span>}</span>
<span>// Traditional array processing</span>
<span>double</span><span>[]</span> <span>prices</span> <span>=</span> <span>{</span><span>100.0</span><span>,</span> <span>200.0</span><span>,</span> <span>300.0</span><span>,</span> <span>400.0</span><span>};</span>
<span>double</span> <span>discountFactor</span> <span>=</span> <span>0.9</span><span>;</span>
<span>double</span><span>[]</span> <span>discountedPrices</span> <span>=</span> <span>new</span> <span>double</span><span>[</span><span>prices</span><span>.</span><span>length</span><span>];</span>
<span>for</span> <span>(</span><span>int</span> <span>i</span> <span>=</span> <span>0</span><span>;</span> <span>i</span> <span><</span> <span>prices</span><span>.</span><span>length</span><span>;</span> <span>i</span><span>++)</span> <span>{</span>
    <span>discountedPrices</span><span>[</span><span>i</span><span>]</span> <span>=</span> <span>prices</span><span>[</span><span>i</span><span>]</span> <span>*</span> <span>discountFactor</span><span>;</span>
<span>}</span>
<span>// Vector API approach</span>
<span>try</span> <span>(</span><span>var</span> <span>vector</span> <span>=</span> <span>DoubleVector</span><span>.</span><span>fromArray</span><span>(</span><span>prices</span><span>,</span> <span>0</span><span>))</span> <span>{</span>
    <span>var</span> <span>discounted</span> <span>=</span> <span>vector</span><span>.</span><span>mul</span><span>(</span><span>discountFactor</span><span>);</span>
    <span>discounted</span><span>.</span><span>intoArray</span><span>(</span><span>prices</span><span>,</span> <span>0</span><span>);</span>
<span>}</span>
// Traditional array processing
double[] prices = {100.0, 200.0, 300.0, 400.0};
double discountFactor = 0.9;
double[] discountedPrices = new double[prices.length];
for (int i = 0; i < prices.length; i++) {
    discountedPrices[i] = prices[i] * discountFactor;
}
// Vector API approach
try (var vector = DoubleVector.fromArray(prices, 0)) {
    var discounted = vector.mul(discountFactor);
    discounted.intoArray(prices, 0);
}

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The Vector API automatically leverages CPU-specific optimizations, ensuring optimal performance across different architectures without requiring manual optimization efforts.

Practical Benefits

These modernization features offer several advantages:

Performance Improvements

Stream Gatherers reduce memory allocation and copying AOT loading eliminates startup overhead Vector API leverages hardware-level parallelism

Code Simplification

Single-pass operations reduce boilerplate
More declarative programming style
Better alignment with functional programming principles

Development Efficiency

Faster prototyping with instant startup
Easier parallelization of computations
Reduced chance of manual optimization errors

原文链接：Java 24: Unlocking Enhanced Performance and Modern Development Capabilities

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