maxMemory refers to the maximum possible current virtual machine memory use, xmx configuration parameters for jvm
totalMemory refers to the current virtual machine runtime memory used, when you start the virtual machine, equipped with xms parameters, then the memory is configured value, then the project will be run as a virtual machine initial increase in current use, the maximum possible increased to maxMemory
freeMemory refers to the current virtual machine has been applied for but not used in the memory, the memory is not used to produce the situation in two ways:
1, equipped with xms parameters, such as the configuration of the xms 1G, when there jvm start, had applied for a 1G of memory, while the program is running, if only a 0.5G memory, then freeMemory is 1-0.5 = 0.5G
2, the program is running, it will need to gradually along with the application from the operating system memory, and the amount of application will be more than the required amount, it will produce freeMemory, this value is generally small