Java objects reside in an area called the heap, while metadata such as class objects and method objects reside in the permanent generation or Perm Gen area. The permanent generation is not part of the heap.
The heap is created when the JVM starts up and may increase or decrease in size while the application runs. When the heap becomes full, garbage is collected. During the garbage collection objects that are no longer used are cleared, thus making space for new objects.
-Xmssize Specifies the initial heap size.
-Xmxsize Specifies the maximum heap size.
-XX:MaxPermSize=size Sets the maximum permanent generation space size. This option was deprecated in JDK 8, and superseded by the -XX:MaxMetaspaceSize option.
Sizes are expressed in bytes. Append the letter k or K to indicate kilobytes, m or M to indicate megabytes, g or G to indicate gigabytes.
How is the java memory pool divided?
Java (JVM) Memory Model – Memory Management in Java