I have the below Java code excert. I am expecting to see the keys printed in a sorted manner (since I am using a TreeMap), but it is not sorting the keys. What I am missing?
CODE:
public class TreeMapTest {
static TreeMap<String,String> li=new TreeMap<String,String>();
static void readAndPrint(){
for (Map.Entry<String, String> entry:li.entrySet() ){
System.out.println(entry);
}
}
public static void main(String[] args) {
for (int i=0;i<10;i++){
String key = String.valueOf(new Random().nextInt(100));
String item = UUID.randomUUID().toString().substring(30);
li.put(key,item);
System.out.println(MessageFormat.format("inserting ({0},{1})",key,item));
}
readAndPrint();
}
}
Sample output:
inserting (7,f4b66a) inserting (2,5f417d) inserting (51,90bb9f) inserting (99,4bfb73) inserting (41,a4e9d5) inserting (14,9286d6) inserting (44,ec4fbd) inserting (58,e7dd3a) inserting (69,c54e66) inserting (0,d1fbfe) 0=d1fbfe 14=9286d6 2=5f417d 41=a4e9d5 44=ec4fbd 51=90bb9f 58=e7dd3a 69=c54e66 7=f4b66a 99=4bfb73
As you see I am not getting the elements sorted ( I sometimes have the output sorted and sometime have it not sorted as above!). What I am missing or misunderstanding?
Answer
They are sorted, by the default sort order of Strings. Strings are ordered lexicographically, so "14" is considered less than "2".
If you want numerical sort order, you should have made the keys Integers instead of Strings.