Java - get index of key in HashMap

Question

In java if I am looping over the keySet   of a HashMap  how do I  inside the loop   get the numerical index of that key   Basically  as I loop through the map  I want to be able to get 0 1 2   I figure this would be cleaner than declaring an int and incrementing with each iteration   Thanks

User · Answer

Simply put  hash-based collections aren t indexed so you have to do it manually

User · Answer

If all you are trying to do is get the value out of the hashmap itself  you can do something like the following   for  Object key   map keySet          Object value   map get key         TODO  this     Or  you can iterate over the entries of a map  if that is what you are interested in   for  Map Entry lt Object  Object gt  entry   map entrySet          Object key   entry getKey        Object value   entry getValue          TODO  other cool stuff     As a community  we might be able to give you better more appropriate answers if we had some idea why you needed the indexes or what you thought the indexes could do for you

User · Answer

I was recently learning the concepts behind Hashmap and it was clear that there was no definite ordering of the keys  To iterate you can use   Hashmap lt String Integer gt  hs new Hashmap    for Map Entry lt String  Integer gt  entry   hs entrySet           String key entry getKey          int val entry getValue            your code block

User · Answer

I don t know is this what you re looking for List keys   new ArrayList map keySet     int index   keys indexOf element

User · Answer

You can t - a set is unordered  so there s no index provided  You ll have to declare an int  as you say  Just remember that the next time you call keySet   you won t necessarily get the results in the same order

User · Answer

The HashMap has no defined ordering of keys

User · Answer

Posting this as an equally viable alternative to  Binil Thomas s answer - tried to add it as a comment  but was not convinced of the readability of it all   int index   0   for  Object key   map keySet         Object value   map get key        index      Probably doesn t help the original question poster since this is the literal situation they were trying to avoid  but may aid others searching for an easy answer

User · Answer

Not sure if this is any  cleaner   but   List keys   new ArrayList map keySet     for  int i   0  i  lt  keys size    i          Object obj   keys get i          do stuff here

User · Answer

Use LinkedHashMap instead of HashMap It will always return keys in same order  as insertion  when calling keySet    For more detail  see Class LinkedHashMap

[java] Java - get index of key in HashMap?

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