Java Runtime get total memory and free memory

public class Main {
  public static void main(String args[]) {
    Runtime r = Runtime.getRuntime();
    long m1, m2;//from w  ww  . j  a va 2s  .c o m
    Integer someints[] = new Integer[1000];

    System.out.println("Total memory is: " + r.totalMemory());

    m1 = r.freeMemory();
    System.out.println("Initial free memory: " + m1);
    r.gc();
    m1 = r.freeMemory();
    System.out.println("Free memory after garbage collection: " + m1);

    for (int i = 0; i < 1000; i++) {
      someints[i] = new Integer(i); // allocate integers
    }
    m2 = r.freeMemory();
    System.out.println("Free memory after allocation: " + m2);
    System.out.println("Memory used by allocation: " + (m1 - m2));

    // discard Integers
    for (int i = 0; i < 1000; i++) {
      someints[i] = null;
    }
    r.gc(); // request garbage collection

    m2 = r.freeMemory();
    System.out.println("Free memory: " + m2);

  }
}