What is Garbage Collection in Java?

Safalta Expert Published by: Aryan Rana Updated Mon, 03 Oct 2022 12:14 AM IST

Highlights

Java programmers must deal with the challenge of destroying things that are no longer needed. However, this can be easily handled with the help of the garbage collector. By discarding things without a reference, this garbage collector's primary goal is to release heap memory. The process is called garbage collection.

Table of Content

What does Java's garbage collection mean?
What's the process of garbage collection?
Types of Garbage Collector 
Advantages
Ideal Techniques


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What does Java's garbage collection mean?


Java programmers must deal with the challenge of destroying things that are no longer needed. However, this can be easily handled with the help of the garbage collector. By discarding things without a reference, this garbage collector's primary goal is to release heap memory. The process is called garbage collection.

It is additionally regarded as a tool for automatic memory management. Objects are produced on the heap, which is actually memory reserved for the program when Java programs are launched on the JVM.

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Some things will eventually become obsolete. To release some memory, the garbage collector discovers these useless objects and deletes them.
  • When there is no more memory in the system to allocate, programs that do not de-allocate memory may eventually crash. These applications are all alleged to have memory leaks.
  • Java's automatic garbage collection prevents memory leaks by removing the need to de-allocate memory throughout the course of a program.
  • In C and C++, methods like free() and delete() are employed, while in Java, the operation is carried out automatically. Java thus offers superior memory management.


What's the process of garbage collection?


The process of garbage collection involves dealing with the heap memory as well as marking or identifying inaccessible things and compaction-based destruction of them.

In Java, garbage collection is an automatic process; objects do not need to be explicitly marked for deletion. The JVM is where the implementation is mostly found. Garbage collection can be implemented by each JVM. The JVM specification should be met as the only prerequisite.

Despite the large number of JVMs that are available, Oracle's HotSpot is by far the most popular because it provides a complete and well-developed set of garbage collection options.
  • The HotSpot features a number of garbage collectors that are each tailored for different use cases and adhere to the same fundamental workflow.
  • Unreferenced items are found and designated as being ready for garbage collection in the first stage.
  • The marked objects are eliminated in the following phase. After the garbage collector removes items, memory can optionally be compacted such that any remaining objects are in a contiguous block at the top of the heap. Following the block of memory allotted to current items in a sequential order is made simpler by the compaction process.

The generational collecting approach used by HotSpot's waste collectors groups items according to their age. The most common things have a short lifespan and will be ready for garbage collection soon after production, which is the justification for generational garbage collection.
 

Types of Garbage Collector 


The four garbage collectors offered by the JVM are all generational. Each one has unique benefits and drawbacks. The user decides which garbage collector to employ, and there might be significant variations in performance and program pauses.

There are four distinct categories of garbage collectors.
  • Serial Garbage Collector (GC): All garbage collection operations are carried out sequentially within a single thread. After each garbage collection, consolidation is done.
  • Parallel/throughput GC: Minor/small garbage collection uses many threads. Major garbage collection and Old Generation compaction are done in a single thread. Additionally, for significant garbage collection and Old Generation compaction, the Parallel version makes use of many threads.
  • CMS Collector: The same algorithm as Parallel is applied over a number of threads for small/minor garbage collection. The majority of garbage collection is multi-threaded, however, CMS runs concurrently with the application processes to reduce application events. There is no compaction.
  • G1 Collector: In essence, CMS is going to be replaced by this trash collector. Similar to CMS, it is parallel and concurrent, but when compared to the more traditional garbage collectors, it operates very differently.


Advantages

  • The primary advantage of Java garbage collection is that it takes care of the automatic eradication of useless objects and certain inaccessible objects to free up memory space.
  • Garbage Collection has recently become a required element in many well-known programming languages.
  • Thus, Java becomes memory-efficient. It is a result of the garbage collector clearing off the heap memory of unreferenced objects.
  • The garbage collector, which is a component of JVM, performs it automatically.


Ideal Techniques


Setting JVM flags is the best way to adjust to Java garbage collection. Flags can change how the waste collector is employed. It contributes to making it the most appropriate choice for backend processing where extended garbage collection breaks are permitted.

Another thing to keep in mind is that the CMS garbage collector is built to reduce pauses, making it perfect for GUI applications where responsiveness is crucial. By altering the size of the heap or one of its portions and monitoring garbage collection effectiveness, adjustments can be made further.

How does Java handle garbage collection?

Garbage collection happens automatically in Java throughout the course of a program. As a result, there is no need to deallocate memory, which prevents memory leaks. Java programs automatically manage their memory through a process known as Java Garbage Collection.

What is the best garbage collector?

With very big (multi-terabyte) heaps, ZGC, a low-latency garbage collector, performs well. Similar to G1, ZGC runs in parallel with the application. ZGC is region-based, concurrent, single-generation, NUMA-aware, and compacting. The execution of application threads is not halted for longer than 10ms.

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