causes of memory leaks in java

Causes of Memory Leaks in Java and How to Avoid Them

Java offers a lot of benefits, and one of the best benefits of using it is JVM (Java Virtual Machine). It is out-of-the-box memory management. Users create various objects, and Java Garbage Collector is always used to take care of memory allocation and keep the memory free for further usage. Even though there are several cases when the memory leaks still happen in most of the Java applications.

If you are worried about the memory leaks in Java, then it is the time when you can forget your worries. As we have explained all the useful details about memory leaks in Java. So, without wasting more time, scroll down to get all the details.

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In this article, we discuss all the useful ways of the cause of memory leaks in java.

What is Memory Leak?

Memory leaks happen when the objects are no longer to use. And Garbage Collector is unable to delete them because they are referenced.

To understand the meaning, you need to understand the memory status of the objects. The diagram below shows the situation when the leaks happen.


It has been seen that there are two different types of object source: referenced objects and unreferenced objects. Unreferenced objects are collected as unused objects. At the same time, the referenced objects are collected as usable objects. Unreferenced objects certainly are not used because any other object is already referencing them.

Here, the GC keeps on eliminating the unreferenced objects, but it is able to get the unused objects that are referenced. This is the situation when the memory leaks in Java happen.

In which conditions, the memory leaks happen?

A memory leak happens when the developer allocates a portion of the memory in a heap and forgets to remove it. In non-garbage-collected languages, objects on the heap lead to memory leaks until they are released.

In Java, the responsibility for handling memory deallocation is passed on to the Garbage Collector (GC). So developers shouldn’t worry about this at all. But still, there are some cases when the leaks in Java still happen.

The cause of memory leaks in the Java language is a situation where the application no longer uses some objects. Still, the Garbage Collector does not recognize them as unused and release them.

How do users identify the memory leaks in Java?

There are some situations in which you can notice that there are memory leaks. Once you noticed the below-mentioned symptoms, try to fix them as soon as possible. The common symptoms of memory leaks are:

  • There is a severe performance issue with the use of the large data set.
  • If the spontaneous crashes keep on happening.
  • In the situation when the old generating objects are still using the memory in the JVM.
  • If there is any issue and out-of-memory heap errors keep on occurring in JVM.
BONUS: Is there any tool that can recognize useless objects?

Yes, some tools are available that do memory management and identify each useless object or leak. These tools are:

* IBM Tivoli
* JProbe

How to avoid the memory leak?

It has been seen that there are memory leaks in Java; that is why it is necessary to fix the issue of leaks. There are two different ways to fix this issue and these ways are:

  1.  Quick fix: Eclipse Memory Leak Warnings
  2. Manually disable & enable parts of your code and observe memory usage of your JVM 
  • Quick fix: Eclipse Memory Leak Warnings

For code that complies with JDK 1.5 +, the eclipse will give alerts and errors to you for obvious cases of leakage. To be more accurate, implement the closable that will always give a warning to you about whether referenced is destroyed or not. Yet, leak detection in eclipse projects is always not enabled. Maybe you need to turn them in first. Go to the settings of your project and allow them to demonstrate:

Enable Leak detection in eclipse

Yet not all file closures and leaks detected even with fancy Eclipse hocus pocus. Especially when working with legacy code (pre 1.5), you are likely to run into leaks. Because they write before being implemented as ‘closable.’ Or sometimes, opening/closures of files nested so deeply that they detected by the eclipse.

  • Manually disable & enable parts of your code and observe memory usage of your JVM 

If you’ve got that far, you need to roll up all efforts and do some manual work. You read all of your code and try to decide out where the leak happens. To help with this process: I recommend that you try using a tool such as VisualVM.

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Configure VisualVM

  • Download the tool.
  • Open terminal, navigate to …/visual Xyz/bin, and run the ‘./visualvm.’ shell script 
  • The main window should be visible. If you expand ‘local’ and double-click your running application (in my case, a child’s eclipse), you can see its.

  • Troubleshooting VisualVM on Fedora: Initially, you will face issues with the troubleshooting, but if you follow the below-mentioned steps, then you can easily operate JVM.
  1. Make sure you run it as your own user, rather than sudo.
  2. Carry out a full system update.
  3. Rebooting helps you
  4. Try to close all Java applications running on it. Launch VisualVM again and try your luck.
  • Add some plugins:

To add the plugin, go to Tools -> select Plugins -> check  ‘Available Plugins.’ Finally, select the below-mentioned plugins:

  1. Memory Pools
  2. Visual GC
  3. Kill Application

Memory Leak of java Application:

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Additional methods: How to Find Leak Sources in Your Java Application?

  These are the following additional ways to find the leak in java Application:

  • Verbose Garbage Collection

One of the fastest ways of identifying a memory leak is to allow for repetitive garbage collection.

Adding the verbose: Add GC parameter to our application’s JVM configuration that allows for a very detailed GC trace. In the default error output file, summary reports are displayed, which should help you understand how your memory is being managed.

  • Do Profiling

The second technique is the one that we’ve been using throughout this article – and that’s profiling. The most famous profiler is Visual VM – which is a good place to start moving past command-line JDK tools into lightweight profiling.

  • Review Your Code

Lastly, this is more of general good practice than a particular technique to deal with memory leakage.

Put – thoroughly review your code, conduct regular code reviews, and use static analytics tools to help you understand your code and system.


It is critical to have the techniques and tools to see what is going on at the Java code’s runtime. Static analysis and careful code-focused reviews can only do a little bit. But on the runtime, you will end up with the more complex leaks that aren’t identifiable in the code immediately.

Lastly, leaks are difficult to find, and they keep on generating as many of them, and they generally cause Memory Leaks in Java. This is where you have to go beyond the code-level analysis and work on two main aspects: early detection and fix immediately.

So, follow all the methods mentioned above to fix the memory leaks in Java. If you are still facing any issue with any point related to a memory leak, comment in the below section, and we will try to help you out in the best possible way.

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Frequently Asked Questions

Are memory leaks permanent?

It has been noticed that memory leaks do not cause any physical or permanent damage. Being a software issue, it slows down the application that is in current use, or even it can slow the whole system. However, a single program takes RAM spaces, but it doesn’t always mean that there is memory leakage somewhere.

What is heap memory?

The heap considers as a memory that is utilized by programming languages where the global variables store. By default, each global variable is stored within the heap memory space as it supports Dynamic memory allocation. It is known to all that heap is not managed automatically, but the CPU manages it.

What are memory leaks in Java?

The standard definition of a memory leak is a situation that happens while the application no longer utilizes objects. However, the GC cannot remove them from working memory as all are still taken as references.

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