get string value from HashMap depending on key name

Question

I have a HashMap with various keys and values  how can I get one value out   I have a key in the map called my code  it should contain a string  how can I just get that without having to iterate through the map   So far I ve got       HashMap newMap   new HashMap paramMap      String s   newMap get  my code   toString      I m expecting to see a String  such as  ABC  or  DEF  as that is what I put in there initially  but if I do a System out println   I get something like java lang string F0454  Sorry  I m not too familiar with maps as you can probably guess

User · Answer

If you are storing keys values as strings  then this will work   HashMap lt String  String gt  newMap   new HashMap lt String  String gt     newMap put  my code    shhh secret    String value   newMap get  my code      The question is what gets populated in the HashMap  key  amp  value

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An important point to be noted here is that if your key is an object of user-defined class in java then make it a point to override the equals method  Because the HashMap get Object key  method uses the equals method for matching the key value  If you do not override the equals method then it will try to find the value simply based on the reference of the key and not the actual value of key in which case it will always return a null

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Suppose you declared HashMap as  -   HashMap lt Character Integer gt  hs   new HashMap lt  gt       Then key in map is of type Character data type and value of int type Now to get value corresponding to key irrespective of type of key value type  syntax is  -      char temp    a       if hs containsKey temp            int val   hs get temp     val is the value corresponding to key temp         So  according to your question you want to get string value corresponding to a key For this  just declare HashMap as HashMap lt  datatype of key   datatype of value  hs   new HashMap lt      Using this will make your code cleaner and also you don t have to convert the result of hs get  my code   to string as by default it returns value of string if at entry time one has kept value as a string

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This is another example of how to use keySet    get    values   and entrySet   functions to obtain Keys and Values in a Map           Map lt Integer  String gt  testKeyset   new HashMap lt Integer  String gt              testKeyset put 1   first            testKeyset put 2   second            testKeyset put 3   third            testKeyset put 4   fourth                Print a single value relevant to a specified Key   uses keySet            for int mapKey  testKeyset keySet                System out println testKeyset get mapKey                Print all values regardless of the key          for String mapVal  testKeyset values                System out println mapVal trim                 Displays the Map in Key-Value pairs  e g   1 first  2 second  3 third  4 fourth           System out println testKeyset entrySet

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Just use Map get key     Object value   map get myCode     Here s a tutorial about maps  you may find it useful  http   java sun com docs books tutorial collections interfaces map html   Edit  you edited your question with the following      I m expecting to see a String  such as  ABC  or  DEF  as that is what I put in there initially  but if I do a System out println   I get something like java lang string F0454      Sorry  I m not too familiar with maps as you can probably guess      You re seeing the outcome of Object toString    But the java lang String should already have one implemented  unless you created a custom implementation with a lowercase s in the name  java lang string  If it is actually a custom object  then you need to override Object toString   to get a  human readable string  whenever you do a System out println   or toString   on the desired object  For example    Override public String toString         return  This is Object X with a property value     value

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HashMap lt Integer  String gt  hmap   new HashMap lt Integer  String gt      hmap put 4   DD      The Value mapped to Key 4 is DD

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You can use the get Object key  method from the HashMap  Be aware that i many cases your Key Class should override the equals method  to be a useful class for a Map key

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If you will use Generics and define your map as   Map lt String String gt  map   new HashMap lt String String gt       then fetching value as    String s   map get  keyStr       you wont be required to typecast the map get   or call toString method to get String value

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map get myCode

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Your question isn t at all clear I m afraid  A key doesn t have a  name   it s not  called  anything as far as the map is concerned - it s just a key  and will be compared with other keys  If you have lots of different kinds of keys  I strongly suggest you put them in different maps for the sake of sanity   If this doesn t help  please clarify the question - preferrably with some code to show what you mean

[java] get string value from HashMap depending on key name

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