HashMap - getting First Key value

Question

Below are the values contain in the HashMap  statusName  Active 33  Renewals Completed 3  Application 15    Java code to getting the first Key  i e Active   Object myKey   statusName keySet   toArray   0     How can we collect the first Key  Value   i e 33   I want to store both the  Key  and  Value  in separate variable

User · Answer

Improving whoami s answer  Since findFirst   returns an Optional  it is  a good practice to check if there is a value    var optional   pair keySet   stream   findFirst      if   optional isPresent          return       var key   optional get      Also  some commented that finding first key of a HashSet is unreliable  But sometimes we have HashMap pairs  i e  in each map we have one key and one value  In such cases finding the first key of such a pair quickly is convenient

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You can also try below     Map Entry lt String  Integer gt  entry   myMap firstEntry    System out println  First Value       entry

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To get the  first  value   map values   toArray   0    To get the value of the  first  key   map get map keySet   toArray   0     Note  Above code tested and works   I say  first  because HashMap entries are not ordered   However  a LinkedHashMap iterates its entries in the same order as they were inserted - you could use that for your map implementation if insertion order is important

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Remember that the insertion order isn t respected in a map generally speaking  Try this                   Get the first element of a map  A map doesn t guarantee the insertion order         param map         param  lt E gt          param  lt K gt          return             public static  lt E K gt  K getFirstKeyValue Map lt E K gt  map           K value   null          if map    null  amp  amp  map size    gt  0               Map Entry lt E K gt  entry    map entrySet   iterator   next                if entry    null                  value   entry getValue                      return  value          I use this only when I am sure that that map size      1

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Note that you should note that your logic flow must never rely on accessing the HashMap elements in some order  simply put because HashMaps are not ordered Collections and that is not what they are aimed to do   You can read more about odered and sorter collections in this post    Back to the post  you already did half the job by loading the first element key   Object myKey   statusName keySet   toArray   0     Just call map get key  to get the respective value   Object myValue   statusName get myKey

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You may also try the following in order to get the entire first entry  Map Entry lt String  String gt  entry   map entrySet   stream   findFirst   get    String key   entry getKey    String value   entry getValue     The following shows how you may get the key of the first entry  String key   map entrySet   stream   map Map Entry  getKey  findFirst   get       or better String key   map keySet   stream   findFirst   get     The following shows how you may get the value of the first entry  String value   map entrySet   stream   map Map Entry  getValue  findFirst   get       or better String value   map values   stream   findFirst   get     Moreover  in case wish to get the second  same for third etc  item of a map and you have validated that this map contains at least 2 entries  you may use the following  Map Entry lt String  String gt  entry   map entrySet   stream   skip 1  findFirst   get    String key   map keySet   stream   skip 1  findFirst   get    String value   map values   stream   skip 1  findFirst   get

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Java 8 way of doing   String firstKey   map keySet   stream   findFirst   get

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Also a nice way of doing this     Map lt Integer JsonObject gt  requestOutput   getRequestOutput client post   int statusCode   requestOutput keySet   stream   findFirst   orElseThrow    - gt  new RuntimeException  Empty

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how can we collect the first Key  Value   i e 33    By using youMap get keyYouHave   you can get the value of it      want to store the Both  Key  and  Value  in separate variable   Yes  you can assign that to a variable   Wait          it s not over    If you business logic  are depending on the order of insertions and retrieving  you are going to see weird results  Map is not ordered they won t store in an order  Please be aware of that fact  Use some alternative to preserve your order  Probably a LinkedHashMap

User · Answer

You can try this    Map lt String String gt  map   new HashMap lt  gt      Map Entry lt String String gt  entry   map entrySet   iterator   next     String key   entry getKey     String value   entry getValue      Keep in mind  HashMap does not guarantee the insertion order  Use a LinkedHashMap to keep the order intact   Eg    Map lt String String gt  map   new LinkedHashMap lt  gt      map put  Active   33     map put  Renewals Completed   3     map put  Application   15     Map Entry lt String String gt  entry   map entrySet   iterator   next     String key  entry getKey     String value entry getValue     System out println key    System out println value     Output    Active  33

[java] HashMap - getting First Key value

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