What is the default garbage collector used? What others do you know?

By default, modern versions of the JVM (starting from Java 9) use the G1 (Garbage-First) garbage collector. It is optimized for multi-processor systems and large heaps, aiming to minimize pause times during garbage collection.

Other well-known garbage collectors in the JVM include:

• Serial GC — single-threaded, simple, suitable for small applications.
• Parallel GC (Throughput Collector) — multi-threaded, focused on maximum throughput.
• CMS (Concurrent Mark Sweep) — aims to minimize pauses, works in parallel with the application.
• ZGC — a low-latency, scalable garbage collector for large heaps.
• Shenandoah — similar to ZGC, with low pauses.

The choice of garbage collector depends on requirements for latency, throughput, and heap size.