HashMap VS TreeMap memory footprint

Main.java

import org.openjdk.jol.info.GraphLayout;

import java.util.HashMap;
import java.util.Map;
import java.util.TreeMap;

public class Main {

  static final int SIZE = 1<<18;
  static final double LOAD_FACTOR = 0.75;

  public static void main(String[] args) {


    int elemCount = (int)(SIZE * LOAD_FACTOR) - 10;

    measureMapFootprint(new HashMap<String, String>(SIZE), elemCount);
    measureMapFootprint(new TreeMap<String, String>(), elemCount);
  }

  static void measureMapFootprint(Map<String, String> map, int elemCount) {
    for (int i = 0; i < elemCount; i++) {
      map.put(Integer.toString(i), Integer.toString(i));
    }

    System.out.println(GraphLayout.parseInstance(map).totalSize());
    System.out.println(GraphLayout.parseInstance(map).toFootprint());
  }
}

stdout.txt

29198752
java.util.HashMap instance footprint:
 COUNT       AVG   SUM      DESCRIPTION
 393196       31   12422272 [C
 393196       24    9436704 java.lang.String
     1        48         48 java.util.HashMap
     1   1048592    1048592 [Ljava.util.HashMap$Node;
 196598       32    6291136 java.util.HashMap$Node
 982992             29198752 (total)

29722944
java.util.TreeMap instance footprint:
 COUNT       AVG  SUM DESCRIPTION
 393196       31  12422272 [C
 393196       24   9436704 java.lang.String
     1        48        48 java.util.TreeMap
 196598       40   7863920 java.util.TreeMap$Entry
 982991           29722944 (total)