Garbage Collection How It Works?

Garbage collection (GC) in Java is the process of automatically identifying and reclaiming memory that is no longer in use, ensuring that unused objects are removed from the heap memory. This helps in preventing memory leaks and optimizing performance by freeing up memory for new objects.

In Java, the garbage collection mechanism is managed by the Java Virtual Machine (JVM). It works by identifying objects that are no longer referenced by any part of the program and then reclaiming the memory occupied by those objects.

Key concepts related to Java garbage collection:

1. Heap Memory: This is where Java objects are stored during runtime. The garbage collector manages the heap memory by removing objects that are no longer in use.
2. References: An object is eligible for garbage collection when there are no active references pointing to it.
3. Generations: Java heap memory is divided into generations (Young, Old, and Permanent generations). Garbage collection occurs more frequently in the Young generation, where newly created objects are placed.
4. Garbage Collection Algorithms:
   • Mark-and-Sweep: The process begins by marking live objects and then sweeping through the memory to remove unreferenced ones.
   • Generational Collection: This method divides objects into generations (young and old), with different collection strategies for each generation.
   • Stop-the-world event: A brief pause occurs during garbage collection to allow the JVM to reclaim memory.

Types of Garbage Collectors in Java:

• Serial Garbage Collector
• Parallel Garbage Collector
• Concurrent Mark-Sweep (CMS) Collector
• G1 Garbage Collector

Why Garbage Collection is Important:

• Reduces the need for manual memory management, thus minimizing human error.
• Ensures efficient use of memory, improving application performance.
• Helps avoid memory leaks by automatically reclaiming unused memory.

Common Interview Questions on Garbage Collection:

1. What is garbage collection in Java, and how does it work?
2. What are the different types of garbage collectors in Java, and how do they differ?
3. What is the difference between heap memory and stack memory in Java?
4. Explain the concept of “reachability” and how it affects garbage collection.
5. What is the purpose of the finalize() method in Java, and how is it related to garbage collection?
6. Can we force garbage collection in Java? If yes, how?
7. What is the impact of garbage collection on application performance?