Printing HashMap In Java

Question

I have a HashMap   private HashMap lt TypeKey  TypeValue gt  example   new HashMap lt TypeKey  TypeValue gt       Now I would like to run through all the values and print them   I wrote this   for  TypeValue name   this example keySet          System out println name       It doesn t seem to work   What is the problem   EDIT  Another question  Is this collection zero based  I mean if it has 1 key and value will the size be 0 or 1

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Useful to quickly print entries in a HashMap  System out println Arrays toString map entrySet   toArray

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Assuming you have a Map lt KeyType  ValueType gt   you can print it like this   for  Map Entry lt KeyType  ValueType gt  entry   map entrySet          System out println entry getKey         entry getValue

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You want the value set  not the key set   for  TypeValue name  this example values              System out println name       The code you give wouldn t even compile  which may be worth mentioning in future questions -  doesn t seem to work  is a bit vague

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A simple way to see the key value pairs   Map lt String  Integer gt  map   new HashMap lt  gt     map put  a   1   map put  b   2   System out println Arrays asList map       method 1 System out println Collections singletonList map       method 2   Both method 1 and method 2 output this     b 2  a 1

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You can use Entry class to read HashMap easily   for Map Entry lt TypeKey  TypeKey gt  temp   example entrySet         System out println temp getValue        Or something as per temp defination  can be used

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For me this simple one line worked well   Arrays toString map entrySet   toArray

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map forEach  key  value  - gt  System out println key         value      Using java 8 features

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I did it using String map  if you re working with String Map    for  Object obj   dados entrySet          Map Entry lt String  String gt  entry    Map Entry  obj      System out print  Key      entry getKey         System out println    Value      entry getValue

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Worth mentioning Java 8 approach  using BiConsumer and lambda functions   BiConsumer lt TypeKey  TypeValue gt  consumer    o1  o2  - gt              System out println o1          o2    example forEach consumer     Assuming that you ve overridden toString method of the two types if needed

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You have several options   Get map values     which gets the values  not the keys Get the map entrySet   which has both Get the keySet   and for each key call map get key

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If the map holds a collection as value  the other answers require additional effort to convert them as strings  such as Arrays deepToString value toArray     if its a map of list values   etc   I faced these issues quite often and came across the generic function to print all objects using ObjectMappers  This is quite handy at all the places  especially during experimenting things  and I would recommend you to choose this way   import com fasterxml jackson databind ObjectMapper  import com fasterxml jackson databind SerializationFeature   public static String convertObjectAsString Object object        String s           ObjectMapper om   new ObjectMapper        try           om enable SerializationFeature INDENT OUTPUT           s   om writeValueAsString object         catch  Exception e            log error  error converting object to string -     e             return s

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A simple print statement with the variable name which contains the reference of the Hash Map would do    HashMap lt K V gt  HM   new HashMap lt  gt       empty System out println HM     prints key value pairs enclosed in      This works because the toString  method is already over-ridden in the AbstractMap class which is extended by the HashMap Class More information from the documentation      Returns a string representation of this map  The string representation consists of a list of key-value mappings in the order returned by the map s entrySet view s iterator  enclosed in braces         Adjacent mappings are separated by the characters       comma and space   Each key-value mapping is rendered as the key followed by an equals sign       followed by the associated value  Keys and values are converted to strings as by String valueOf Object

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To print both key and value  use the following   for  Object objectName   example keySet         System out println objectName      System out println example get objectName

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Java 8 new feature forEach style   import java util HashMap   public class PrintMap       public static void main String   args            HashMap lt String  Integer gt  example   new HashMap lt  gt             example put  a   1           example put  b   2           example put  c   3           example put  d   5            example forEach  key  value  - gt  System out println key           value             Output          a   1         b   2         c   3         d   5

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keySet   only returns a set of keys from your hashmap  you should iterate this key set and the get the value from the hashmap using these keys   In your example   the type of the hashmap s key is TypeKey  but you specified TypeValue in your generic for-loop  so it cannot be compiled  You should change it to    for  TypeKey name  example keySet                 String key   name toString                String value   example get name  toString                  System out println key         value          Update for Java8    example entrySet   forEach entry- gt       System out println entry getKey           entry getValue                If you don t require to print key value and just need the hashmap value  you can use others  suggestions      Another question  Is this collection   is zero base  I mean if it has 1 key   and value will it size be 0 or 1    The collection returned from keySet   is a Set You cannot get the value from a Set using an index  so it is not a question of whether it is zero-based or one-based  If your hashmap has one key  the keySet   returned will have one entry inside  and its size will be 1

[java] Printing HashMap In Java

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