How Do I Determine the Default Maximum Java Heap Size?

Determining the Default Max Java Heap Size

When the '-Xmxn' option is not specified in the Java command line, a default maximum heap size is used. As per Java documentation, this value "is chosen at runtime based on system configuration." This article aims to delve into the specific system configuration settings that influence the default max heap size.

Windows System

To obtain the default heap size on a Windows system where the Java application is running, execute the following command:

java -XX:+PrintFlagsFinal -version | findstr HeapSize

This command will display the options 'MaxHeapSize' (for -Xmx) and 'InitialHeapSize' (for -Xms) and provide you with the respective default values.

Unix/Linux System

On a Unix or Linux system, issue the command below to determine the default heap size:

java -XX:+PrintFlagsFinal -version | grep HeapSize

The output will include the options 'MaxHeapSize' and 'InitialHeapSize', along with their default values expressed in bytes.

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