Demonstrate totalMemory(), freeMemory() and gc(). : Runtime System « Development « Java Tutorial

1. Java Tutorial
2. Development
3. Runtime System

class MemoryDemo {
  public static void main(String args[]) {
    Runtime r = Runtime.getRuntime();
    long mem1, mem2;
    Integer someints[] = new Integer[1000];

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

    mem1 = r.freeMemory();
    System.out.println("Initial free memory: " + mem1);
    r.gc();
    mem1 = r.freeMemory();
    System.out.println("Free memory after garbage collection: " + mem1);

    for (int i = 0; i < 1000; i++)
      someints[i] = new Integer(i); // allocate integers

    mem2 = r.freeMemory();
    System.out.println("Free memory after allocation: " + mem2);
    System.out.println("Memory used by allocation: " + (mem1 - mem2));

    for (int i = 0; i < 1000; i++)
      someints[i] = null;

    r.gc(); // request garbage collection

    mem2 = r.freeMemory();
    System.out.println("Free memory after collecting" + " discarded Integers: " + mem2);

  }
}