Java is one of the world’s most widely used technologies, and with its growth has come a rich ecosystem of multiple JDK vendors and multiple JVM implementations.
Understanding the differences among them is essential, especially when you’re tuning performance, deploying to production, or choosing a runtime for long-term stability.

Part 1: JDK Vendors — Oracle vs OpenJDK vs Others

1. What Is a JDK?

A Java Development Kit (JDK) includes:

• Java compiler (javac)
• Java runtime (java)
• Standard library (rt.jar or modular equivalents)
• JVM implementation (HotSpot or others)
• Tools (profilers, debuggers, monitoring tools)

While the Java language and its specifications are standardized, the JDK implementation can differ depending on the vendor.

2. The Two Main JDK Families

2.1 OpenJDK (The Reference Implementation)

OpenJDK is:

• The official open-source Java implementation
• Managed by Oracle + community contributors
• The foundation for most modern JDKs
• Free under the GPL v2 + Classpath Exception

Every six months, OpenJDK releases a new version.

Key Points:

• Source code is open
• Vendors create builds from OpenJDK source
• Performance and feature set identical across most distributions
• HotSpot JVM included by default

OpenJDK is the true standard of modern Java.

2.2 Oracle JDK

Oracle JDK is:

• Oracle’s commercial build of OpenJDK
• Historically had extra features and tools
• Now nearly identical to OpenJDK in modern versions (Java 11+)

Oracle provides:

• Paid commercial support
• Enterprise-grade security patches
• Tools like Java Flight Recorder and Mission Control (previously Oracle-exclusive but now open-sourced)

Differences with OpenJDK:

Feature	OpenJDK	Oracle JDK
Source code	Fully open	Mostly open
Cost	Free	Free for dev use; paid support for production
Performance	Same	Same
Updates	Every 6 months, community builds	Quarterly security patches with support
Tools	Some require separate download	Bundled and integrated

Today, Oracle JDK = OpenJDK + commercial support.

3. Other Major JDK Vendors

Modern Java is extremely modular and vendor-friendly. Many companies build their own JDKs using OpenJDK source, adding optimizations, support policies, or integrations.

Below are the most important distributions.

3.1 Eclipse Temurin (formerly AdoptOpenJDK)

• The most popular free OpenJDK build today
• Trusted by enterprises
• Backed by the Eclipse Foundation
• HotSpot JVM by default

Use case:
Most developers and enterprises who want a stable, free JDK choose Eclipse Temurin.

3.2 Amazon Corretto

• AWS-managed OpenJDK distribution
• Free and long-term supported
• Available for Linux, Windows, and macOS
• Tuned for cloud workloads

Use case:
If you’re deploying to AWS, Corretto is ideal.

3.3 Azul Zulu & Azul Zing

Azul provides two types of JDKs:

1. Azul Zulu (OpenJDK build)

• Free builds
• Stable
• Widely used in enterprise

2. Azul Zing (proprietary JVM)

• Uses the Falcon JIT compiler
• Includes C4, a pauseless garbage collector
• Designed for ultra-low-latency systems (HFT, trading, fraud detection)

Use case:
For extreme low latency requirements, Azul is unmatched.

3.4 BellSoft Liberica JDK

• Popular for embedded systems
• Includes Full JRE and “Lite” versions
• Strong support for ARM devices
• Fully compatible with JavaFX builds

Use case:
IoT, embedded systems, and GUI applications.

3.5 GraalVM by Oracle

A special JVM distribution that includes:

• Ahead-of-time compilation (native image)
• Faster performance for some workloads
• Polyglot capabilities (JS, Python, Ruby, R)

Use case:
Cloud-native microservices that require fast startup (e.g., serverless).

Summary Table: JDK Vendors at a Glance

Vendor	JVM	Strength
Oracle JDK	HotSpot	Enterprise support, stability
OpenJDK	HotSpot	Open source reference
Eclipse Temurin	HotSpot	Most trusted free build
Amazon Corretto	HotSpot	AWS-optimized
Azul Zulu	HotSpot	Enterprise builds
Azul Zing	Proprietary C4	Ultra-low latency
Liberica JDK	HotSpot	Embedded/IoT
GraalVM	Graal	Fast startup, polyglot

Part 2: JVM Implementations —HotSpot vs OpenJ9 vs Others

The JVM is the engine that runs your Java programs.

Most developers assume there is only one JVM, but there are multiple implementations.

1. HotSpot JVM — The Industry Standard

HotSpot is the default JVM used by:

• Oracle JDK
• OpenJDK
• Amazon Corretto
• Eclipse Temurin
• BellSoft Liberica
• Azul Zulu

If you didn’t explicitly install another JVM, you are using HotSpot.

HotSpot strengths:

• Highly optimized
• Mature and battle-tested
• Excellent garbage collectors (G1, ZGC, Shenandoah)
• Extremely stable
• Best for most server, desktop, and cloud workloads
• Highly tunable
• Massive ecosystem compatibility

HotSpot JIT Compilers:

• C1 (client compiler) → startup speed
• C2 (server compiler) → long-running optimization
• Tiered compilation → combines both for best performance

2. Eclipse OpenJ9 — A Lightweight Alternative

OpenJ9 is an alternative JVM created by IBM, now maintained by Eclipse.

OpenJ9 focuses on:

• Lower memory usage
• Fast startup times
• Smaller runtime footprint

This makes it ideal for:

• Microservices
• Serverless computing
• Docker/Kubernetes deployments
• Memory-constrained environments

Key differences from HotSpot:

Feature	HotSpot	OpenJ9
Startup time	Good	Excellent
Memory usage	Moderate	Low
Throughput performance	High	Moderate
GC options	Many (G1, ZGC, Shenandoah)	Fewer
Maximum optimization	Higher	Lower

Should you switch to OpenJ9?

Use OpenJ9 if:

• You run hundreds of containers
• You need fast startup
• You want reduced RAM consumption

Stick with HotSpot if:

• You need maximum throughput
• You rely on heavy GC tuning
• You run high-performance applications

3. Other JVM Implementations

3.1 GraalVM (Oracle)

The GraalVM runtime includes:

• A high-performance JIT compiler
• Optional native image ahead-of-time compilation
• Polyglot capabilities

Great for:

• Serverless functions
• Lightweight microservices
• Multi-language applications

3.2 Azul Prime (formerly Zing)

Uses a proprietary JVM with C4 (Continuously Concurrent Compacting Collector):

• Near-zero garbage collection pauses
• Built for low-latency workloads

Great for:

• High-frequency trading
• Fraud detection
• Real-time analytics
• Telecom systems

3.3 Dalvik/ART (Android JVMs)

These run on mobile devices and are part of Android’s ecosystem.

They are not used for server-side Java, but they follow JVM principles.

4. Choosing the Right JVM for Your Needs

Choose HotSpot if you want:

1. Best overall performance
2. Broadest compatibility
3. Huge user community
4. Mature GC algorithms
5. Enterprise stability

Default and recommended for 90% of Java systems.

Choose OpenJ9 if you want:

1. Lower memory footprint
2. Faster startup
3. Better for containers
4. Better for serverless workloads

Recommended for microservices and cloud-native architectures.

Choose GraalVM (native image mode) if you want:

1. Instant startup
2. Minimal memory usage
3. Extremely lightweight binaries

Ideal for serverless and very small services.

Choose Azul Prime if you want:

1. No GC pauses
2. High-frequency, low-latency performance

Ideal for trading, real-time AI, telecom.