Question

I have a List of HashMap such as below

ArrayList l = new ArrayList ();
HashMap m = new HashMap ();
m.add("site_code","AL");
m.add("site_name","Apple");
l.add(m);
m = new HashMap();
m.add("site_code","JL");
m.add("site_name","Cat");
l.add(m);
m = new HashMap();
m.add("site_code","PL");
m.add("site_name","Banana");
l.add(m)

I’d like to sort the list based on site_name. So in the end it would be sorted as.

Apple, Banana, Cat

I was trying something like this:

Collections.sort(l, new Comparator(){
           public int compare(HashMap one, HashMap two) {
              //what goes here?
           }
});

Answer 1

If you make your collections generic, it will end up looking about like this:

Collections.sort(l, new Comparator<HashMap<String, String>>(){ 
        public int compare(HashMap<String, String> one, HashMap<String, String> two) { 
            return one.get("site_name").compareTo(two.get("site_name"));
        } 
});

If you can’t use generics because you’re stuck on a 1.4 or earlier platform, then you’ll have to cast the get‘s to String.

(Also, as a matter of style, I’d prefer declaring the variables as List and Map rather than ArrayList and HashMap. But that’s not relevant to the question.)