Question

My List contains House objects with the following fields:

private Integer address;
private String street;
private double price;
private int rooms;

I would like to generate a report that lists the number rooms, how many house have that quantity of rooms, and then a listing of those houses. Similar to below.

houses with 2 rooms: 3

-Mainstreet, 1112, $45,000.00

-Mainstreet, 1456, $42,200.00

-Oak, 54, 43,600.00

houses with 3 rooms: 1

-Mainstreet, 1890, $52,000.00

I was thinking of a hashmap with room/quantity key pairs and then using the hashmap to build an array, but there has to be something easier than running a bunch of loops. Any suggestions?

Answer 1

This is what you need:

Map<Integer, List<House>> map = new HashMap<Integer, List<House>>();

Then iterate once over over your list to build the map.

for(House h: houses){
    List<House> l = map.get(h.rooms);
    if(l==null){ 
        l = new ArrayList<House>();
        map.put(h.rooms, l);
    }
    l.add(h);
}

map.get(3) will return list houses having 3 rooms;

Then you are done.