how to conveniently get first element or last element from LinkedHashMap?

Question

I hava a structure Map :

Map<String, Double> map = new LinkedHashMap<>();

I don't know the key, but I want to pick up the first element and the last element, how can I achieve conveniently.

http://stackoverflow.com/questions/1936462/java-linkedhashmap-get-first-or-last-entry — Matthias, Nov 27 '15 at 14:37
have a look at it . http://stackoverflow.com/questions/1936462/java-linkedhashmap-get-first-or-last-entry — Kumaresan Perumal, Nov 27 '15 at 14:37

score 2 · Answer 1 · edited May 23 '17 at 11:47

2

Getting the first is easy - request an iterator and take it's next.

// Needs null checks etc.
String first = map.keySet().iterator().next();

Getting the last is covered in Java get last element of a collection.

edited May 23 '17 at 11:47

Community

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1

answered Nov 27 '15 at 14:49

OldCurmudgeon

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or [use reflection](http://stackoverflow.com/a/33960155/829571) :-) – assylias Nov 27 '15 at 15:06

score 1 · Accepted Answer · edited Jun 20 '20 at 09:12

one way to do this:

    Map<String, Double> map = new LinkedHashMap<>();
    map.put("one", 2.0);
    map.put("two", 12.0);
    map.put("three", 44.0);
    String lKeyFirst = null;
    String lKeyLast = null;
    if (!map.isEmpty()){
      lKeyFirst = map.keySet().iterator().next();
      for(String key : map.keySet()){
        lKeyLast = key;
      }
      System.out.println("First key: " +lKeyFirst);
      System.out.println("Last key: " +lKeyLast);
    }

Output:

First key: one

Last key: three

of course isEmpty is never false in this case.

EDIT:

@Test
public void testMapOneValue() {
Map<String, Double> map = new LinkedHashMap<>();
map.put("one", 2.0);
String lKeyFirst = null;
String lKeyLast = null;
if (!map.isEmpty()){
  lKeyFirst = map.keySet().iterator().next();
  for(String key : map.keySet()){
    lKeyLast = key;
  }
  System.out.println("First key: " +lKeyFirst);
  System.out.println("Last key: " +lKeyLast);
}
}

Output:

First key: one

Last key: one

how to conveniently get first element or last element from LinkedHashMap?

2 Answers2