Print all key value pairs in a Java ConcurrentHashMap

Question

I am trying to simply print all key value pair s  in a ConcurrentHashMap    I found this code online that I thought would do it  but it seems to be getting information about the buckets hashcode  Actually to be honest the output it quite strange  its possible my program is incorrect  but I first want to make sure this part is what I want to be using   for  Entry lt StringBuilder  Integer gt  entry   wordCountMap entrySet          String key   entry getKey   toString        Integer value   entry getValue        System out println  key      key     value     value       This gives output for about 10 different keys  with counts that seem to be the sum of the number of total inserts into the map

User · Accepted Answer

I tested your code and works properly  I ve added a small demo with another way to print all the data in the map   ConcurrentHashMap lt String  Integer gt  map   new ConcurrentHashMap lt String  Integer gt     map put  A   1   map put  B   2   map put  C   3    for  String key   map keySet          System out println key         map get key       for  Map Entry lt String  Integer gt  entry   map entrySet          String key   entry getKey   toString        Integer value   entry getValue        System out println  key      key     value     value

User · Answer

The HashMap has forEach as part of its structure  You can use that with a lambda expression to print out the contents in a one liner such as    map forEach  k v - gt  System out println k      v     or  map forEach  k v - gt  System out println  key    k    value    v

User · Answer

Work 100  sure try this code for the get all hashmap key and value   static HashMap lt String  String gt  map   new HashMap lt  gt      map put  one     a      map put  two     b      map put  three     c      map put  four     d        just call this method whenever you want to show the HashMap value   private void ShowHashMapValue                             get the Set Of keys from HashMap                     Set setOfKeys   map keySet            get the Iterator instance from Set             Iterator iterator   setOfKeys iterator            Loop the iterator until we reach the last element of the HashMap             while  iterator hasNext             next   method returns the next key from Iterator instance     return type of next   method is Object so we need to do DownCasting to String                 String key    String  iterator next            once we know the  key   we can get the value from the HashMap    by calling get   method                 String value   map get key                System out println  Key      key      Value      value

User · Answer

The ConcurrentHashMap is very similar to the HashMap class  except that ConcurrentHashMap offers internally maintained concurrency  It means you do not need to have synchronized blocks when accessing ConcurrentHashMap in multithreaded application   To get all key-value pairs in ConcurrentHashMap  below code which is similar to your code works perfectly     Initialize ConcurrentHashMap instance ConcurrentHashMap lt String  Integer gt  m   new ConcurrentHashMap lt String  Integer gt        Print all values stored in ConcurrentHashMap instance for each  Entry lt String  Integer gt  e   m entrySet        System out println e getKey       e getValue         Above code is reasonably valid in multi-threaded environment in your application  The reason  I am saying  reasonably valid  is that  above code yet provides thread safety  still it can decrease the performance of application   Hope this helps you

User · Answer

You can do something like  Iterator iterator   map keySet   iterator     while  iterator hasNext         String key   iterator next   toString       Integer value   map get key       System out println key         value       Here  map  is your concurrent HashMap

User · Answer

best and simple way to show keys and values        initialize map     Map lt Integer  String gt  map   new HashMap lt Integer  String gt           Add some values     map put 1   Hi        map put 2   Hello            iterate map using entryset in for loop     for Entry lt Integer  String gt  entry   map entrySet              print keys and values          System out println entry getKey            entry getValue                 Result        1   Hi     2   Hello

[java] Print all key/value pairs in a Java ConcurrentHashMap

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