This document discusses several updates in Java 13, including expression switches with the yield keyword, text blocks for multi-line strings, reimplementation of the legacy socket API, ZGC returning unused memory to the OS, and dynamic class data sharing archives for reducing startup time and memory footprint. It provides code examples of the new expression switch and text block features.

1. sbordet@webtide.com
Java 13 - Updates
@simonebordet

2. sbordet@webtide.com
Simone Bordet
● @simonebordet
● sbordet@webtide.com
● Java Champion
● Works @ Webtide
● The company behind Jetty and CometD
● JVM Tuning Expert

3. sbordet@webtide.com
Java 13 - Updates
● JEP 354 - Expression switch (preview)
○ Was JEP 325 in Java 12
○ Prepares for pattern matching (JEP 305)
○ All cases enforced by the compiler
$ java --enable-preview
boolean workDay = switch(dayOfWeek) {
case SATURDAY, SUNDAY -> false;
default -> true;
}

4. sbordet@webtide.com
Java 13 - Updates
● Use yield <expr> to return a value
○ In Java 12 it was break <expr>
boolean workDay = switch (day) {
case SATURDAY, SUNDAY -> {
System.err.println("Weekend");
yield false;
}
default -> true;
}

5. sbordet@webtide.com
Java 13 - Updates
● But also:
boolean workDay = switch (day) {
case SATURDAY, SUNDAY: {
System.err.println("Weekend");
yield false;
}
default:
yield true;
}

6. sbordet@webtide.com
Java 13 - Updates
● Switch expression can use colon or arrow syntax
○ Cannot be mixed
● Colon syntax: allows for fall-through
● Arrow syntax -> NO fall-through

7. sbordet@webtide.com
Java 13 - Updates
● JEP 355 - Text Blocks (preview)
○ Was JEP 326 (Raw String Literals) in Java 12
■ Withdrawn
String json = """
__{"o": "JUG Torino",
__"y": 2001
}""";
=> "__{"o": "JUG Torino",n__"y": 2001n}"

8. sbordet@webtide.com
Java 13 - Updates
● Margin management
String json = """
__{"o": "JUG Torino",
__"y": 2001
}__""";
=> "{"o": "JUG Torino",n"y": 2001n}"

9. sbordet@webtide.com
Java 13 - Updates
● Special cases
String empty = """
""";
String error = """{
}""";
Error: illegal text block open delimiter sequence

10. sbordet@webtide.com
Java 13 - Updates
● JEP 353 - Reimplement the Legacy Socket API
● Complete rewrite of the Socket implementation
○ Also to prepare for Project Loom
● To restore old implementation
○ -Djdk.net.usePlainSocketImpl
● Outstanding job from Oracle
○ Jetty runs tests and apps without a single problem

11. sbordet@webtide.com
Java 13 - Updates
● JEP 351 - ZGC: Uncommit Unused Memory
● Feature implemented by Shenandoah and G1
○ G1 implemented it in Java 12
● When -Xms != -Xmx memory is returned to OS
○ Good in the cloud to pay less
● Memory is returned during GC
○ If JVM is idle, GC is scheduled after a delay

12. sbordet@webtide.com
Java 13 - Updates
● JEP 350 - Dynamic CDS Archives
○ Extends JEP 310 - Application Class Data Sharing
● Reduces startup time & memory footprint
● To create the archive
○ -XX:ArchiveClassesAtExit=app.jsa
● To use the archive
○ -XX:SharedArchiveFile=app.jsa

13. sbordet@webtide.com
Java 13 - Updates
● References
● https://jdk.java.net/13/release-notes
● New Features
● Removed Features
● Deprecated Features
● API Differences with Java 12

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