Java

Garbage Collectors

Meet the cleaning crew: Serial, Parallel, CMS, G1, and ZGC.

By TechCoder TeamLast updated: 2026-06-02
In a Nutshell

Meet the cleaning crew: Serial, Parallel, CMS, G1, and ZGC. This hands-on tutorial focuses on practical implementation of garbage collectors concepts.

Garbage Collectors

Java has multiple Garbage Collectors (GC) for different use cases.

Key Concepts

  • Stop-the-World: The application pauses while GC runs. We want to minimize this time.
  • Throughput: Percentage of total time spent running app vs running GC.

Types of GC

  1. Serial GC: Single-threaded. Good for small apps/client-side.
    • -XX:+UseSerialGC
  2. Parallel GC: Multiple threads for minor GC. High throughput. Default in older Java versions.
    • -XX:+UseParallelGC
  3. G1 GC (Garbage First): The default for Java 9+. Splits Heap into regions. Balances throughput and pause time. Best for servers with large memory.
    • -XX:+UseG1GC
  4. ZGC (Z Garbage Collector): Scalable, low latency. Targeting sub-millisecond pauses.
    • -XX:+UseZGC

Interactive Code

Trigger a GC (Request only!)

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Quiz

Quiz

Question 1 of 3

What does 'Stop-the-World' mean?

The internet stops
The JVM pauses application execution
The computer shuts down

Next Steps

Theory is over. Let's connect to a real database in Module 15: Database Connectivity.