How is the default max Java heap size determined?

The default maximum heap size for the Java heap is determined by the amount of physical memory available on the system. The Java Virtual Machine (JVM) uses a formula to calculate the default maximum heap size based on the amount of physical memory detected on the system.

Here is the formula used by the JVM to calculate the default maximum heap size:

• For systems with less than 1 GB of physical memory, the default maximum heap size is set to 256 MB.
• For systems with 1 GB or more of physical memory, the default maximum heap size is set to 1/4 of the physical memory up to a maximum of 1 GB.

For example, on a system with 4 GB of physical memory, the default maximum heap size would be calculated as follows:

1/4 * 4 GB = 1 GB

Since 1 GB is less than the maximum of 1 GB, the default maximum heap size would be set to 1 GB.

You can override the default maximum heap size by specifying the -Xmx command-line option when starting the JVM. For example, to set the maximum heap size to 2 GB, you would use the following command:

java -Xmx2g MyClass

I hope this helps! Let me know if you have any other questions.