HashMap should be unsorted but still sorts according to key

Question

According to these:

1. http://docs.oracle.com/javase/6/docs/api/java/util/HashMap.html
2. Difference between HashMap, LinkedHashMap and TreeMap
3. jav

Answer 1

It's pure coincidence. Sometimes it appears to be sorted, but keep adding keys and the dream will shatter.

I wrote this little program:

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

class MapTest {

    public static void main(String[] args){
        int count = Integer.parseInt(args[0]);
        Map map = new HashMap();
        for (int i = 0; i < count; i++) map.put(i, i);
        System.out.println(map);
    }

}

When running java MapTest 20, I get the following output (line-wrapped for readability):

{0=0, 1=1, 2=2, 3=3, 4=4, 5=5, 6=6, 7=7, 8=8, 9=9, 10=10, 11=11, 12=12, 13=13, 
14=14, 15=15, 17=17, 16=16, 19=19, 18=18}

It's simply a property of the implementation of HashMap that Integers added sequentially (and starting at 0) at first seem to be ordered.