public class test {
  public static void main(String[] args) {
    long start = System.nanoTime();
    final int size = 1024*1024*1024;
    byte[] buffer = new byte[size];
    for (int i = 0; i < size - 1; i += 4096) buffer[i] = (byte) 255;
    System.out.println("Total time: " + (System.nanoTime() - start + 512*1024) / (1024*1024) + " ms.");
  }
}

Total time: 395 ms.

public class test {
  public static void main(String[] args) {
    int size = 512;
    if (args.length > 0) {
      try { size = Integer.parseInt(args[0]); }
      finally {}
    }
    if (size < 0) size = 512;
    if (size > 1024) size = 512;
    Runtime rt = Runtime.getRuntime();
    System.out.print("Memory: " + (rt.totalMemory() + 512*1024)/1024/1024 + " Mb total / ");
    System.out.println((rt.freeMemory() + 512/1024)/1024/1024 + " Mb free");
    long start = System.nanoTime();
    size *= 1024*1024;
    int[] buffer = new int[size];
    for (int i = 0; i < size - 1; i += 4096) buffer[i] = -1;
    System.out.print("  Time: " + (System.nanoTime() - start + 512*1024) / (1024*1024) + " ms total (");
    System.out.println((size * 4L + 512*1024)/1024/1024 + " Mb buffer)");
    System.out.print("Memory: " + (rt.totalMemory() + 512*1024)/1024/1024 + " Mb total / ");
    System.out.println((rt.freeMemory() + 512/1024)/1024/1024 + " Mb free.");
  }
}

java -Xms5000m test 833
Memory: 4792 Mb total / 4741 Mb free
  Time: 1220 ms total (3332 Mb buffer)
Memory: 4792 Mb total / 1409 Mb free.

public class test {
  public static void main(String[] args) {
    int size = 512;
    if (args.length > 0) {
      try { size = Integer.parseInt(args[0]); }
      catch (NumberFormatException e) {}
      finally {}
    }
    if (size < 1) size = 512;
    if (size > 1024) size = 512;
    size *= 1024*1024;

    int[] buffer = new int[0]; buffer = null;

    Runtime rt = Runtime.getRuntime();
    System.out.print("Memory: " + (rt.totalMemory() + 512*1024)/1024/1024 + " Mb total / ");
    System.out.println((rt.freeMemory() + 512/1024)/1024/1024 + " Mb free");

    long start = System.nanoTime();
    buffer = new int[size]; buffer[buffer.length - 1] = -1;
    System.out.print("  Time: " + (System.nanoTime() - start + 512*1024)/1024/1024 + " ms total (");
    System.out.println((4L * buffer.length + 512*1024)/1024/1024 + " Mb buffer)");

    buffer = null; System.gc();

    start = System.nanoTime();
    buffer = new int[size]; buffer[buffer.length - 1] = -1;
    System.out.print("  Time: " + (System.nanoTime() - start + 512*1024)/1024/1024 + " ms total (");
    System.out.println((4L * buffer.length + 512*1024)/1024/1024 + " Mb buffer)");
    System.out.print("Memory: " + (rt.totalMemory() + 512*1024)/1024/1024 + " Mb total / ");
    System.out.println((rt.freeMemory() + 512/1024)/1024/1024 + " Mb free.");
  }
}

Memory: 4907 Mb total / 4855 Mb free
  Time: 2 ms total (4 Mb buffer)
  Time: 1 ms total (4 Mb buffer)
Memory: 4907 Mb total / 4851 Mb free.
 
Memory: 4907 Mb total / 4855 Mb free
  Time: 6 ms total (16 Mb buffer)
  Time: 2 ms total (16 Mb buffer)
Memory: 4907 Mb total / 4839 Mb free.
 
Memory: 4907 Mb total / 4855 Mb free
  Time: 23 ms total (64 Mb buffer)
  Time: 20 ms total (64 Mb buffer)
Memory: 4907 Mb total / 4791 Mb free.
 
Memory: 4907 Mb total / 4855 Mb free
  Time: 92 ms total (256 Mb buffer)
  Time: 44 ms total (256 Mb buffer)
Memory: 4907 Mb total / 4599 Mb free.
 
Memory: 4907 Mb total / 4855 Mb free
  Time: 369 ms total (1024 Mb buffer)
  Time: 146 ms total (1024 Mb buffer)
Memory: 4907 Mb total / 3832 Mb free.
 
Memory: 4907 Mb total / 4855 Mb free
  Time: 1211 ms total (3332 Mb buffer)
  Time: 451 ms total (3332 Mb buffer)
Memory: 4907 Mb total / 1523 Mb free.