无法按升序对列表进行排序

时间:2013-10-09 06:01:02

标签: java android sorting arraylist treemap

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);
}

id = 1,3,5,57,80

的输入值

金额的输入值= 100,500,200,10,10000

无法按金额的升序对列表进行排序。它仍按插入顺序显示。

我该如何解决这个问题?我感谢任何帮助。提前谢谢。

预期产出:金额升序:

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

5 个答案:

答案 0 :(得分:2)

假设这是你的输入

  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);

这是您的分类代码

  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);
    }

<强>输出

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

<强>更新

如果值为十进制,则使用以下代码替换return Integer.parseInt(value1)-Integer.parseInt(value2);

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

答案 1 :(得分:1)

使用sort()

例如:

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

System.out.println(list)

现在它将按照其包含的内容类型的升序打印列表。

答案 2 :(得分:1)

否..您不能使用默认排序方法根据值缩短任何地图。 您应该编写自定义方法进行排序。 看到这个链接 - TreeMap sort by value

如果你想按键排序,我建议使用treemap。

谢谢!

答案 3 :(得分:1)

您必须使用自定义Comparator并在Treemap的构造函数中传递它。例如,在比较器之后使用金额进行排序:

请参阅以下链接。它肯定会解决你的问题

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

答案 4 :(得分:1)

默认情况下,列表未排序。您需要Collections.sort()方法Comparator。所以看起来你想按amount排序,你应该像下面这样实现比较器。

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));
    }
});

这是完整的工作副本,

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);

它应该打印,

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