How Does Java Determine its Default Heap Size?

Discovering the Factors Determining Default Java Heap Size

In Java, omitting the -Xmx option during command line execution prompts the Java Virtual Machine (JVM) to assign a default heap size. The documentation suggests that this value is determined dynamically based on the system configuration.

To unravel the specific system configurations affecting the default heap size, let's explore the methods of retrieving these settings on Windows and Unix/Linux systems:

Windows:

1. Run the following command:

   java -XX:+PrintFlagsFinal -version | findstr HeapSize

2. Identify the values for MaxHeapSize (-Xmx) and InitialHeapSize (-Xms)

Unix/Linux:

1. Execute the command:

   java -XX:+PrintFlagsFinal -version | grep HeapSize

The resulting output should display the default heap sizes, typically in bytes.

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