无法按升序对列表进行排序

Question

Map<String, String> map ;
List<Map<String, String>> list = new ArrayList<Map<String, String>>();


/////OnCreate.............


function1(){
map = new TreeMap<String, String>();
map.put("id", "id");
map.put("amont", "amount");

list.add(map);

System.out.println(list);
}

input values for id=1,3,5,57,80

input values for amount=100,500,200,10,10000

Unable to sort the list by ascending order of amount. It still shows in the order it was inserted.

How do I fix this? I appreciate any help. Thanks in advance.

Expected output: Ascending order of amount:

amt=10 id=4  
amt=100 id=1  
amt=200 id=3  
amt=500 id=2  
amt=10000 id=5  

Answer 1

Assuming this is your input

  Map<String, String> map ;
  List<Map<String, String>> list = new ArrayList<Map<String, String>>();
  map = new TreeMap<String, String>();
  map.put("id","1");
  map.put("amount","100");
  list.add(map);
  map = new TreeMap<String, String>();
  map.put("id","2");
  map.put("amount","500");  
  list.add(map);
  map = new TreeMap<String, String>();
  map.put("id","3");
  map.put("amount","200");
  list.add(map);
  map = new TreeMap<String, String>();
  map.put("id","4");
  map.put("amount","10");
  list.add(map);
  map = new TreeMap<String, String>();
  map.put("id","5");
  map.put("amount","10000");
  list.add(map);

Here is your sorting code

  Collections.sort(list, new Comparator<Map<String, String>>() {

        @Override
        public int compare(Map<String, String> o1, Map<String, String> o2) {
            String value1 =  o1.get("amount");
            String value2 =  o2.get("amount");
            return Integer.parseInt(value1)-Integer.parseInt(value2);
        }
    });

    for (Map<String, String> map1 : list) {
        String id = map1.get("id");
        String amount = map1.get("amount");
        System.out.println("amount= "+amount + " , " +"id = "+id);
    }

Output

amount= 10 , id = 4
amount= 100 , id = 1
amount= 200 , id = 3
amount= 500 , id = 2
amount= 10000 , id = 5

update

Replace return Integer.parseInt(value1)-Integer.parseInt(value2); with the following code if the values are decimal.

return Double.valueOf(value1).compareTo(Double.valueOf(value2));

Answer 2

Use sort()

Ex:

list.add(map);
Collections.sort(list)

System.out.println(list)

it will now print the list in ascending order of the type of content it contains.

Answer 3

No.. You can't short any map according value using default sort method. You should write your custom method for sorting. see this link- TreeMap sort by value

and I suggest use treemap if you want sorted by key..

Thanks!

Answer 4

You have to use custom Comparator and pass it in Treemap's constructor. For example to sort it with amount use following comparator :

Refer the following link. It will definitely solve your problem

http://java2novice.com/java-collections-and-util/treemap/comparator-user-object/

Answer 5

By default the list is not sorted. You need Collections.sort() method that takes Comparator . So looks like you want to sort by amount , you should implement the comparator like below.

Collections.sort(list, new Comparator<Map<String, String>>() {
    @Override
    public int compare(Map<String, String> o1, Map<String, String> o2) {
        String amount1 = o1.get("amount");
        String amount2 = o2.get("amount");
        return new Integer(amount1).compareTo(new Integer(amount2));
    }
});

Here is the full working copy,

List<Map<String, String>> list = new ArrayList<Map<String, String>>();

Map<String, String> map1 = new TreeMap<String, String>();
map1.put("id", "2");
map1.put("amount", "200");

Map<String, String> map2 = new TreeMap<String, String>();
map2.put("id", "1");
map2.put("amount", "100");

Map<String, String> map3 = new TreeMap<String, String>();
map3.put("id", "3");
map3.put("amount", "300");

list.add(map1);
list.add(map2);
list.add(map3);

Collections.sort(list, new Comparator<Map<String, String>>() {
    @Override
    public int compare(Map<String, String> o1, Map<String, String> o2) {
        String amount1 = o1.get("amount");
        String amount2 = o2.get("amount");
        return amount1.compareTo(amount2);
    }
});

System.out.println(list);

It should print,

[{amount=100, id=1}, {amount=200, id=2}, {amount=300, id=3}]