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Post By Admin Last Updated At 2021-08-24
Understanding Java garbage collection and its importance

In software, it needs to create new features, new objects, and codes always as the old one may not support longer. For this, some programmers have developed the automatic memory management system which is also a key feature of Java. In order to create room for new objects, memory management processes the allocation of new objects by removing the unreachable objects after their use. In Java, developers may need not worry about memory management while writing a program or code. This is due to the feature of Java garbage collection that manages the memory automatically. 

Java Garbage Collection

The major role of Java garbage collection is to identify the unused objects in memory and remove them from the heap memory. This process helps to allocate the new objects to memory smoothly. 

This is, in brief, about what the Java Garbage Collection is, and further in this blog, we will discuss more on this. 

Who does the Java garbage collection?

The Java garbage collection is an automation process where a coder doesn’t need to mark or locate the unused objects to delete. The garbage collector lives in the JVM which automatically detects the unused objects. Moreover, these objects are no longer used in the program and they are removed through Java garbage collection. This feature is useful to make the memory free for new objects. 

There are different ways to unreferenced an object such as through nulling the reference, assigning a reference to another, and through an unknown object. 

Moreover, there are three important steps involved in Java garbage collection which are:

Mark, Sweep, and Compact. 


This is the stage where the Garbage Collector (GC) will mark all the live objects having reference by the app. It makes the process through scanning the heap memory section. If there any object doesn’t have any reference, then it will be eligible for garbage collection. 


In this section within Java garbage collection, the GC will recycle all the objects having no reference from the heap memory.


After performing Sweep, there may be many areas with heap memory that will be empty. This may also cause cleavage. So, the compact stage here helps to arrange the objects in adjacent blocks at the beginning of the heap. Moreover, this process will also help to allocate the new objects in sequential order.

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In the case of traditional coding languages such as C and C++, the programmers have to manually manage the memory management. This is performed within the app through the creation and removal of objects after using them. In this case, there are high chances of a memory leak if the developers missed to delete or remove the objects after using them. 

Hence, automatic memory management in Java plays a major role in the smooth performance of applications. 

What is heap memory in Java?

The objects built by the application in Java resides within a memory known as “Heap Memory”. Actually, the heap is created while the JVM begins. It increases with the usage of the application and gets full after some time. Once the heap usage is full, then there will be no space for the new object’s allocation and then the Java garbage collection begins. All and above we discussed the three different stages that help to delete the unreferenced objects from heap memory and make the space for new objects. 

Further, the heap memory is subdivided into two categories such as - The young generation and Old generation.

Whenever some new objects are built up then they are allocated to the minor/young generation. This again subdivides into Eden space and Survivor space. 

On the other hand, the old generation refers to the objects that lived in the young generation for a long period. They stay for multiple garbage collection cycles. So these objects will be eligible for the promotion to the old generation after completing the threshold limit of multiple GC cycles.  

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Impact of Java garbage collection

The impact of Java garbage collection is that the memory consumption will keep growing with the leakage in memory within the app. This may later result in failure of application with OutOfMemory Errors. The failure happens at a certain point when there is no space for new objects to allocate. 

Java is mainly known for its in-memory database technology but there is a worry of Java garbage collection that impacts app performance. The Java garbage collection is mainly useful for simplifying memory management. Hence, this results in minimized code writing, speedy app development, and also avoid bugs. 

The basic worry about this function is that most of its implementations pause the app’s performance for some time. This mainly happens on the in-memory of the database. 

As the heap size in Java increases, then the heap must reside outside the main or key memory. As a result, it increases the paging activity, and the same impacts Java’s performance. In the meanwhile, a large heap can take a few seconds more time to fill. In this regard, if the Java garbage collection occurs less regularly, then the pause time of garbage collection enhances. 

Java garbage collection best practices

There are many best practices available for Java garbage collection. This is might not considerable consciously by a programmer for many simple apps. But to get the advanced skills in Java, a programmer must importantly know how Java garbage collection works effectively. Also, know the major impacts of this application implementation. The ways it has to tune also is an important part to know. 

The basic mechanism to understand garbage collection is that it is unpredictable. There is no prediction available for it that when it will occur at the run time. But there is a possibility to include a code to run the garbage collector like Runtime.gc () methods. But there is no guarantee that it will help the collector run.

Some common Garbage collection parameters and configurations include Xms, Xmx, Xmn, XX, etc. Further, some common GCs include serial collector, parallel collector, etc. Other than these, there are some most concurrent collectors like CMS and G1.

Moreover, the best practice to tune the Java garbage collection is the set of flags on the JVM. These flags help to adjust the garbage collector usage such as setting the min and max size of the heap, size of the sections of the Java heap, etc. 

For example, the simultaneous garbage collector is a structure but it will regularly cause “stop the world” programs. But it makes it better suited to process backend operations where long stops for collecting garbage are adequate.

Key Garbage Collection metrics to observe

In order to know whether the Java garbage collection is creating issues in its performance. Then a programmer or developer needs to track the whole activities of the GC within the JVM. These activities can be:-

When did the Java garbage collection happen?

How frequently the GC process is happening?

For how long the GC is running?

Time spent by the JVM in the GC process.

Amount of memory collection each time the garbage collection happens.

Type of garbage collection took place - full or minor?

JVM memory usage- heap or non-heap.

These are a few of the activities that need to watch for GC to track the performance. Also, this tracking allows you to locate the garbage collection is taking much time and impacting Java performance. Moreover, you can do optimal settings for each and every app based on past trends.

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Final Words

This is all about the Java garbage collection and its importance. The GC is an important need when there are some unreferenced objects and they need clearance. Hence, one can choose the right garbage collector for his needs based on latency, footprint measurement, throughput, etc. GC will also impact the performance of the functions of the program which may need to notice by the developer or user. 

Therefore, selecting the right GC is purely based on the app requirements and other things. I hope you acquired enough knowledge on Java garbage collection and its various aspects. If you’re planning to learn more on this, get into Core Java Online Training with the ITGuru platform. This learning will give you the real-time experience of working with Java programming.