Question

I’m trying to sort a bunch of data such that that the size of data input to the program can be larger than the memory available to the JVM, and handling that requires external sort which is much slower than Quicksort.

Is there any way of obtaining memory available to the JVM at runtime such that I could use in place sorting as much as possible, and only switch to Mergesort when data input is too large?

Answer 1

Check out these methods on the java.lang.Runtime class:

freeMemory

totalMemory

maxMemory

Example

Runtime rt = Runtime.getRuntime();
System.err.println(String.format("Free: %d bytes, Total: %d bytes, Max: %d bytes",
  rt.freeMemory(), rt.totalMemory(), rt.maxMemory()));

Also note that if the total amount of memory is being exhausted you can always start the JVM with a larger amount of heap allocated using the -Xmx JVM argument; e.g.

java -Xmx256M MyClass