Eclipse – java.lang.OutOfMemoryError: Java heap space

By mkyong | Updated: June 28, 2021

Viewed: 25,087 (+146 pv/w)

Tags: eclipse heap size java error

This article shows how to solve the java.lang.OutOfMemoryError: Java heap space in Eclipse IDE.

Table of contents

• 1. Eclipse – OutOfMemoryError: Java heap space
• 2. Temporary fix – Increase the heap size
• 3. eclipse.ini
• 4. The solution, find the reason behind the heap size error.
• 5. References

1. Eclipse – OutOfMemoryError: Java heap space

In Eclipse IDE, if the Java code is consuming a lot of memory (loading big data at once time) like this :

  // loads a lot of data
  List<Domain> list = domainBo.findAllDomain(100000);

  for(Domain domain : list){
    process(domain.getDomainName());
  }

We hit java.lang.OutOfMemoryError: Java heap space :

Exception in thread "main" java.lang.OutOfMemoryError: Java heap space
  at java.util.HashMap.<init>(HashMap.java:209)
  at java.util.LinkedHashMap.<init>(LinkedHashMap.java:181)

2. Temporary fix – Increase the heap size

On the Eclipse menu, clicks Run -> Run Configurations.., select the Java application we want to run, click on the Arguments tab, VM arguments section, and adjust a better Java initial maximum heap size.

-Xms<size> - Set initial Java heap size
-Xmx<size> - Set maximum Java heap size

For example, -Xms512M -Xmx1024M

3. eclipse.ini

The memory settings in eclipse.ini are allocated to Eclipse IDE only, not the program we want to run. A common mistake is updated the heap size in eclipse.ini, and expects it will solve the heap size error in the program.

But, if no reason constantly crashes the Eclipse IDE, we can increase the heap size and perm gen in eclipse.ini.

  -startu
  openFile
  -showsplash
  //...
  -XX:MaxPermSize=512m
  -Xms512m
  -Xmx1024m
  //...
  -Xdock:icon=../Resources/Eclipse.icns
  -XstartOnFirstThread

P.S Find eclipse.ini in the Eclipse installation folder.

4. The solution, find the reason behind the heap size error.

We can increase the Java heap size to divert the problem temporarily, and the same heap size problem will come back to us later. The real solution is to determine the root cause of the Java heap size error and why we need so much heap size?

In the above code, why we need to load 100k of records at once time? Can we stream the data or process the data by batch?

  // Why? Can you stream it? Or process by batch?
  List<Domain> list = domainBo.findAllDomain(100000);

  for(Domain domain : list){
    process(domain.getDomainName());
  }

If we are not sure what is the root caused, try a profiling tool like Java Flight Recorder to dumps and analyze the JVM.

5. References

• FAQ How do I increase the permgen size available to Eclipse?
• Find Out Your Java Heap Memory Size
• How to simulate java.lang.OutOfMemoryError in Java
• Eclipse + Tomcat – Java.Lang.OutOfMemoryError: Java Heap Space