Java 12 features
Here’s a detailed yet simple list of the key features introduced in Java 12, along with explanations and code examples:
✅ Top Features of Java 12
Released in March 2019, Java 12 was a short-term release with performance enhancements and some powerful new features for developers.
1. 🔹 Switch Expressions (Preview Feature)
Introduced as a preview to simplify and extend the switch statement to return values.
Example:
String day = "MONDAY";
int num = switch (day) {
case "MONDAY", "FRIDAY" -> 6;
case "TUESDAY" -> 2;
default -> 0;
};
System.out.println(num); // Output: 6
✅ More concise and expressive than traditional
switch.
2. 🔹 Default CDS Archives
CDS = Class Data Sharing
Now automatically creates shared class metadata archives for faster JVM startup.
Benefits:
- Faster startup time
- Lower memory usage
No extra configuration needed — it works out of the box.
3. 🔹 Shenandoah Garbage Collector (Experimental)
A low-pause-time GC developed by Red Hat, designed to reduce GC pause times regardless of heap size.
Enable using:
-XX:+UseShenandoahGC
4. 🔹 JVM Constants API (for framework developers)
New APIs to model constant pool entries in class files — useful for tools, compilers, and frameworks.
Classes added:
ConstableConstantDescDynamicConstantDesc
Not for general dev use, but important for tools like Javac, ASM, etc.
5. 🔹 Microbenchmark Suite (JEP 230)
Java 12 added JMH-based microbenchmarking tools directly into the JDK source, to help JVM developers measure performance changes more accurately.
🧪 Only relevant for OpenJDK contributors and performance engineers.
6. 🔹 Abortable Mixed Collections for G1 GC
Improved pause-time predictability in G1 GC by allowing mixed collection sets to be aborted mid-way.
Enhances performance tuning and responsiveness of garbage collection.
7. 🔹 Improved Prompt for jcmd VM.unlock_commercial_features
Better error message when using the old jcmd command that used to unlock commercial features (no longer required after Java 11).
🔚 Summary Table
| Feature | Description |
|---|---|
| 🔁 Switch Expressions (Preview) |
switch returns values; cleaner code |
| 📦 Default CDS Archives | Improves startup time |
| 🧹 Shenandoah GC (Experimental) | Low-pause-time garbage collector |
| 🔣 JVM Constants API | Modeling class-file constants |
| 🧪 Microbenchmark Suite | Benchmarking JVM features |
| 🚫 Abortable G1 GC | Reduced GC pause spikes |
| 📢 jcmd Prompt Improved | Clearer messaging for deprecated commands |
🔧 Run Switch Expressions (Enable Preview)
If you want to use switch expressions in Java 12:
javac --enable-preview --release 12 Test.java
java --enable-preview Test