The following were some of the important enhancements in Java SE 13 and JDK 13:

• Dynamic CDS Archiving extends application class-data sharing (ApsCDS), which allows dynamic archiving of classes when the Java application exits. See JEP 350: Dynamic CDS Archives.
• Text blocks were added to Java language, which provide developers with control over the format when desired. This is a preview language feature. See JEP 355 Text Blocks (Preview) and JEP 12: Preview Language and VM Features.
• The switch expression, a preview language feature, was extended to be used as either a statement or an expression, so that both forms can use either traditional labels (with fall through) or new labels (with no fall through). It is used with a further new statement for yielding a value from a switch expression. See JEP 354: Switch Expressions (Preview) and JEP 12: Preview Language and VM Features.
• The implementation used by java.net.Socket and java.net.ServerSocket APIs was replaced with a simpler and more modern implementation that is easy to maintain and debug. See JEP 353: Reimplement the Legacy Socket API.
• Support for Unicode 12.1. See Unicode 12.1.
• ZGC was enhanced to return unused heap memory to the operating system, which enhances the memory footprint of the applications. See JEP 351 ZGC Uncommit Unused Memory.