how to get the one entry from hashmap without iterating

Question

Is there a elegant way of obtaining only one Entry lt K V gt  from HashMap  without iterating  if key is not known   As order of entry of entry is not important  can we say something like  hashMapObject get zeroth index     Although I am aware that there exist no such get by index method   If I tried approach mentioned below  it would still have to get all the entry set of the hashmap   for Map Entry lt String  String gt  entry   MapObj entrySet          return entry      Suggestions are welcome   EDIT  Please suggest any other Data Structure to suffice requirement

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for getting Hash map first element you can use bellow code in kotlin  val data   Float   hashMap  get hashMap  keys  first

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The answer by Jesper is good  An other solution is to use TreeMap  you asked for other data structures    TreeMap lt String  String gt  myMap   new TreeMap lt String  String gt     String first   myMap firstEntry   getValue    String firstOther   myMap get myMap firstKey       TreeMap has an overhead so HashMap is faster  but just as an example of an alternative solution

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import java util     public class Friday       public static void main String   args            Map lt String  Integer gt  map   new HashMap lt String  Integer gt              map put  code   10           map put  to   11           map put  joy   12            if    map isEmpty                  Map Entry lt String  Integer gt  entry   map entrySet   iterator   next                System out println entry                       This approach doesn t work because you used HashMap  I assume using LinkedHashMap will be right solution in this case

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This would get a single entry from the map  which about as close as one can get  given  first  doesn t really apply   import java util     public class Friday       public static void main String   args            Map lt String  Integer gt  map   new HashMap lt String  Integer gt              map put  code   10           map put  to   11           map put  joy   12            if    map isEmpty                  Map Entry lt String  Integer gt  entry   map entrySet   iterator   next                System out println entry

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Stumbled here looking for the same thing   I then remembered the Iterables class from the Guava library   To get the  first  element  Iterables getFirst  someMap values    null      Essentially does the same as Map values   iterator   next    but also allows you to specify a default  in this case null  should there be nothing in the Map   Iterables getLast  someMap values    null    returns the last element in the Map   Iterables get  someMap values    7  null    returns the 7th element in the Map if exists  otherwise a default value  in this case null    Remember though that HashMaps are not ordered   so don t expect Iterables getFirst to return the first item you tossed in there   likewise with Iterables getLast   Perhaps useful to get a mapped value though   It may not be worth adding the Guava library for just that  but if you happen to be using some of the other cool utilities within that library

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I got the answer  It s simple    Take a ArrayList then cast it and find the size of the arraylist   Here   it is        ArrayList count   new ArrayList        count  ArrayList  maptabcolname get  k1      here  k1  is Key     System out println  number of elements   count size       It will show the size   Give suggestion   It s working

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I guess the iterator may be the simplest solution   return hashMapObject entrySet   iterator   next      Another solution  not pretty    return new ArrayList hashMapObject entrySet    get 0     Or yet  not better    return hashMapObject entrySet   toArray   0

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Why do you want to avoid calling entrySet   it does not generally create an entirely new object with its own context  but instead just provide a facade object  Simply speaking entrySet   is a pretty cheap operation

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If you are using Java 8  it is as simple as findFirst     Quick example   Optional lt Car gt  theCarFoundOpt   carMap values   stream   findFirst     if theCarFoundOpt isPresent          return theCarFoundOpt get   startEngine

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map lt string string gt m  auto it m begin     get iterator to the first element of map m  return m- gt first   return first string 1st string in map lt string string gt m    Incase you want the second string    you can use return m- gt second 2st string in map lt string string gt m    if you want to iterate the whole map you can use loop for auto it m   m is a map    cout lt  lt it- gt first lt  lt endl

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Following your EDIT  here s my suggestion    If you have only one entry  you might replace the Map by a dual object  Depending on the types  and your preferences    an array  of 2 values  key and value  a simple object with two properties

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What do you mean with  without iterating    You can use map entrySet   iterator   next   and you wouldn t iterate through map  in the meaning of  touching each object    You can t get hold of an Entry lt K  V gt  without using an iterator though  The Javadoc of Map Entry says      The Map entrySet method returns a   collection-view of the map  whose   elements are of this class  The only   way to obtain a reference to a map   entry is from the iterator of this   collection-view  These Map Entry   objects are valid only for the   duration of the iteration    Can you explain in more detail  what you are trying to accomplish  If you want to handle objects first  that match a specific criterion  like  have a particular key   and fall back to the remaining objects otherwise  then look at a PriorityQueue  It will order your objects based on natural order or a custom-defined Comparator that you provide

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Maps are not ordered  so there is no such thing as  the first entry   and that s also why there is no get-by-index method on Map  or HashMap    You could do this   Map lt String  String gt  map            wherever you get this from     Get the first entry that the iterator returns Map Entry lt String  String gt  entry   map entrySet   iterator   next       Note  Checking for an empty map omitted    Your code doesn t get all the entries in the map  it returns immediately  and breaks out of the loop  with the first entry that s found   To print the key and value of this first element   System out println  Key    entry getKey      Value    entry getValue       Note  Calling iterator   does not mean that you are iterating over the whole map

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If you really want the API you suggested  you could subclass HashMap and keep track of the keys in a List for example  Don t see the point in this really  but it gives you what you want  If you explain the intended use case  maybe we can come up with a better solution   import java util ArrayList  import java util HashMap  import java util List  import java util Map    SuppressWarnings  unchecked   public class IndexedMap extends HashMap        private List lt Object gt  keyIndex       public IndexedMap             keyIndex   new ArrayList lt Object gt                           Returns the key at the specified position in this Map s keyIndex                  param index                   index of the element to return         return the element at the specified position in this list         throws IndexOutOfBoundsException                    if the index is out of range  index  lt  0    index  gt   size                public Object get int index            return keyIndex get index               Override     public Object put Object key  Object value             addKeyToIndex key           return super put key  value               Override     public void putAll Map source             for  Object key   source keySet                  addKeyToIndex key                     super putAll source              private void addKeyToIndex Object key             if   keyIndex contains key                 keyIndex add key                         Override     public Object remove Object key             keyIndex remove key           return super remove key             EDIT  I deliberately did not delve into the generics side of this

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Get values  convert it to an array  get array s first element   map values   toArray   0    W

[java] how to get the one entry from hashmap without iterating

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