How to get data (key,value) from ListArray

Question

I use the code to Sort the data in the map.

 Map<Integer, Integer> map = new HashMap<>();
    List list = new ArrayList(map.entrySet());
    Collections.sort(list, new Comparator<Map.Entry<Integer, Integer>>() {
        @Override
        public int compare(Map.Entry<Integer, Integer> a, Map.Entry<Integer, Integer> b) {
            return a.getValue() - b.getValue();
        }
    });

I just copy the data from map to List and sort it. How can I get the data from the List? The method get() of list returns just the object, not my 2 integers

Don't use raw types. Your list should be of type List<Map.Entry<Integer, Integer>>. You already seem to know what a Map.Entry is, since you're sorting the list and accessing its value. So what's the problem? Have you read the javadoc of Map.Entry? — JB Nizet
– JB Nizet, Commented Dec 24, 2016 at 10:11

davidxxx · Accepted Answer · 2016-12-24 10:13:40Z

1

You do that :

 List list = new ArrayList(map.entrySet());

You could use generics in your list and then iterate on the Entry of the list after your sorted it:

List<Entry<Integer, Integer>> list = new ArrayList(map.entrySet());
...
// your sort the list
..
// you iterate on key-value
for (Entry<Integer, Integer> entry : list){
  Integer key =  entry.getKey();
  Integer value =  entry.getValue();
}

answered Dec 24, 2016 at 10:13

davidxxx

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2 Comments

Mikhail Nono Over a year ago

Exception in thread "main" java.lang.Error: Unresolved compilation problems: The method values() is undefined for the type List Syntax error, insert ")" to complete EnhancedForStatementHeader at packS.SecondProject.SecondProject.main(SecondProject.java:85)

davidxxx Over a year ago

refresh the page I think. And don't forget to declare the List with the generic type. For the imports, specify those in java.util.

Vasu · Accepted Answer · 2016-12-24 10:41:52Z

1

Your list actually contains elements of type Map.Entry<Integer, Integer>, so you can retrieve the each Entry as shown below:

Map<Integer, Integer> map = new HashMap<>();
//add the values to map here

//Always prefer to use generic types shown below (instead of raw List)
List<Map.Entry<Integer, Integer>> list = new ArrayList<>(map.entrySet());

Collections.sort(list, new Comparator<Map.Entry<Integer, Integer>>() {
  @Override
  public int compare(Map.Entry<Integer, Integer> a,
                  Map.Entry<Integer, Integer> b){
                       return a.getValue() - b.getValue();
    }
  });

  //loop over the list to retrieve the list elements
  for(Map.Entry<Integer, Integer> entry : list) {
        System.out.println(entry.getValue());
  }

edited Dec 24, 2016 at 10:41

answered Dec 24, 2016 at 10:11

Vasu

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2 Comments

Mikhail Nono Over a year ago

My Eclipse can not convert from element type Object to Map.Entry<Integer, Integer>.

JB Nizet Over a year ago

@MikhailNono that's precisely because you declared your list as List, rather than List<Map.Entry<Integer, Integer>>. Read all the answers and comments you got instead of ignoring them. If you didn't ignore them and still have a problem, then edit your question, post your new code, and post the exact and complete error message you get from the compiler.

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