SequencedCollection/Set/Map (Java 21)

• unify collections with a defined order.

• They add first, last, reversed, and add/remove at ends methods.

• Implemented by List, LinkedHashSet, LinkedHashMap, SortedMap, etc.

• Solve the problem of inconsistent handling of ordered collections.

Virtual Threads in Java

✅ What are they?

• Lightweight threads introduced by Project Loom.

• They are not OS threads, but run on top of platform (carrier) threads.

• Created and managed by the JVM, stored in the Java heap (unlike platform threads which are tied to the OS).

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🔑 How they work

• A virtual thread is mounted on a carrier thread (platform thread) when executing.

• If the virtual thread blocks (e.g., waiting on I/O), it is unmounted from the carrier → freeing the carrier thread.

• When ready, it can be remounted on the same or another carrier thread.

• The JVM keeps a snapshot of the virtual thread’s stack frames in the heap during unmount.

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⚙️ Monitoring

• Virtual threads can be monitored using ThreadMXBean from java.lang.management.

• They behave like normal threads for debugging/monitoring purposes, but with much lower resource cost.