How to get Java Memory Heap Size

// Get current size of heap in bytes

long heapSize = Runtime.getRuntime().totalMemory();

// Get maximum size of heap in bytes. The heap cannot grow beyond this size.
// Any attempt will result in an OutOfMemoryException.

long heapMaxSize = Runtime.getRuntime().maxMemory();

// Get amount of free memory within the heap in bytes. This size will increase
// after garbage collection and decrease as new objects are created.

long heapFreeSize = Runtime.getRuntime().freeMemory();