Java LinkedHashMap get first or last entry

The semantics of LinkedHashMap are still those of a Map, rather than that of a LinkedList. It retains insertion order, yes, but that's an implementation detail, rather than an aspect of its interface.

The quickest way to get the "first" entry is still entrySet().iterator().next(). Getting the "last" entry is possible, but will entail iterating over the whole entry set by calling .next() until you reach the last. while (iterator.hasNext()) { lastElement = iterator.next() }

edit: However, if you're willing to go beyond the JavaSE API, Apache Commons Collections has its own LinkedMap implementation, which has methods like firstKey and lastKey, which do what you're looking for. The interface is considerably richer.

Can you try doing something like (to get the last entry):

linkedHashMap.entrySet().toArray()[linkedHashMap.size() -1];

I know that I came too late but I would like to offer some alternatives, not something extraordinary but some cases that none mentioned here. In case that someone doesn't care so much for efficiency but he wants something with more simplicity(perhaps find the last entry value with one line of code), all this will get quite simplified with the arrival of Java 8 . I provide some useful scenarios.

For the sake of the completeness, I compare these alternatives with the solution of arrays that already mentioned in this post by others users. I sum up all the cases and i think they would be useful(when performance does matter or no) especially for new developers, always depends on the matter of each problem

Possible Alternatives

Usage of Array Method

I took it from the previous answer to to make the follow comparisons. This solution belongs @feresr.

  public static String FindLasstEntryWithArrayMethod() {        return String.valueOf(linkedmap.entrySet().toArray()[linkedmap.size() - 1]);    }

Usage of ArrayList Method

Similar to the first solution with a little bit different performance

public static String FindLasstEntryWithArrayListMethod() {        List<Entry<Integer, String>> entryList = new ArrayList<Map.Entry<Integer, String>>(linkedmap.entrySet());        return entryList.get(entryList.size() - 1).getValue();    }

Reduce Method

This method will reduce the set of elements until getting the last element of stream. In addition, it will return only deterministic results

public static String FindLasstEntryWithReduceMethod() {        return linkedmap.entrySet().stream().reduce((first, second) -> second).orElse(null).getValue();    }

SkipFunction Method

This method will get the last element of the stream by simply skipping all the elements before it

public static String FindLasstEntryWithSkipFunctionMethod() {        final long count = linkedmap.entrySet().stream().count();        return linkedmap.entrySet().stream().skip(count - 1).findFirst().get().getValue();    }

Iterable Alternative

Iterables.getLast from Google Guava. It has some optimization for Lists and SortedSets too

public static String FindLasstEntryWithGuavaIterable() {        return Iterables.getLast(linkedmap.entrySet()).getValue();    }

Here is the full source code

import com.google.common.collect.Iterables;import java.math.BigDecimal;import java.math.RoundingMode;import java.util.ArrayList;import java.util.LinkedHashMap;import java.util.List;import java.util.Map;import java.util.Map.Entry;public class PerformanceTest {    private static long startTime;    private static long endTime;    private static LinkedHashMap<Integer, String> linkedmap;    public static void main(String[] args) {        linkedmap = new LinkedHashMap<Integer, String>();        linkedmap.put(12, "Chaitanya");        linkedmap.put(2, "Rahul");        linkedmap.put(7, "Singh");        linkedmap.put(49, "Ajeet");        linkedmap.put(76, "Anuj");        //call a useless action  so that the caching occurs before the jobs starts.        linkedmap.entrySet().forEach(x -> {});        startTime = System.nanoTime();        FindLasstEntryWithArrayListMethod();        endTime = System.nanoTime();        System.out.println("FindLasstEntryWithArrayListMethod : " + "took " + new BigDecimal((endTime - startTime) / 1000000.000).setScale(3, RoundingMode.CEILING) + " milliseconds");         startTime = System.nanoTime();        FindLasstEntryWithArrayMethod();        endTime = System.nanoTime();        System.out.println("FindLasstEntryWithArrayMethod : " + "took " + new BigDecimal((endTime - startTime) / 1000000.000).setScale(3, RoundingMode.CEILING) + " milliseconds");        startTime = System.nanoTime();        FindLasstEntryWithReduceMethod();        endTime = System.nanoTime();        System.out.println("FindLasstEntryWithReduceMethod : " + "took " + new BigDecimal((endTime - startTime) / 1000000.000).setScale(3, RoundingMode.CEILING) + " milliseconds");        startTime = System.nanoTime();        FindLasstEntryWithSkipFunctionMethod();        endTime = System.nanoTime();        System.out.println("FindLasstEntryWithSkipFunctionMethod : " + "took " + new BigDecimal((endTime - startTime) / 1000000.000).setScale(3, RoundingMode.CEILING) + " milliseconds");        startTime = System.currentTimeMillis();        FindLasstEntryWithGuavaIterable();        endTime = System.currentTimeMillis();        System.out.println("FindLasstEntryWithGuavaIterable : " + "took " + (endTime - startTime) + " milliseconds");    }    public static String FindLasstEntryWithReduceMethod() {        return linkedmap.entrySet().stream().reduce((first, second) -> second).orElse(null).getValue();    }    public static String FindLasstEntryWithSkipFunctionMethod() {        final long count = linkedmap.entrySet().stream().count();        return linkedmap.entrySet().stream().skip(count - 1).findFirst().get().getValue();    }    public static String FindLasstEntryWithGuavaIterable() {        return Iterables.getLast(linkedmap.entrySet()).getValue();    }    public static String FindLasstEntryWithArrayListMethod() {        List<Entry<Integer, String>> entryList = new ArrayList<Map.Entry<Integer, String>>(linkedmap.entrySet());        return entryList.get(entryList.size() - 1).getValue();    }    public static String FindLasstEntryWithArrayMethod() {        return String.valueOf(linkedmap.entrySet().toArray()[linkedmap.size() - 1]);    }}

Here is the output with performance of each method

FindLasstEntryWithArrayListMethod : took 0.162 millisecondsFindLasstEntryWithArrayMethod : took 0.025 millisecondsFindLasstEntryWithReduceMethod : took 2.776 millisecondsFindLasstEntryWithSkipFunctionMethod : took 3.396 millisecondsFindLasstEntryWithGuavaIterable : took 11 milliseconds