How to Get Values From Object in Java

Quick recap: In Java, a Map object is used for mapping keys to values. Duplicate keys are not allowed and each key can have at most one value in a map.

Iterating over keys or values (or both) of a Map object is a pretty common use case and one that developers have to do every so often. Fortunately, the Map interface provides three collection views, which allow a map's contents to be viewed:

• as a set of keys
• collection of values, or,
• set of key-value mappings.

Let's walkthrough some examples and see how to get keys, values or both from a map.

1. Using forEach (Java 8+)

Starting from Java 8, forEach is easiest and most convenient way to iterate over all keys and values in a map.

                          map              .              forEach              ((              k              ,              v              )              ->              {              System              .              out              .              println              (              "key: "              +              k              +              ", value: "              +              v              )              });                      

2. Using Map.entrySet() method

Map.entrySet() method returns a Set whose entries are key,value pair of the mappings contained in the Map. This is equivalent to forEach method descried above.

                          // iterate over and get keys and values              for              (              Map              .              Entry              <              Integer              ,              String              >              entry              :              map              .              entrySet              ())              {              Integer              k              =              entry              .              getKey              ();              String              v              =              entry              .              getValue              ();              System              .              out              .              println              (              "key: "              +              k              +              ", value: "              +              v              );              }                      

3. Using map.keySet() method - Keys only

Map.keySet() method returns a Set of keys contained in the map. Use this if you want to obtain the keys only.

                          Set              <              Integer              >              keys              =              map              .              keySet              ();              for              (              Integer              k              :              keys              )              {              System              .              out              .              println              (              "key: "              +              k              );              }                      

4. Using map.values() method - Values only

Map.keySet() method returns a Collection view of the values contained in the map.

                          Collection              <              String              >              values              =              map              .              values              ();              for              (              String              v              :              values              )              {              System              .              out              .              println              (              "value: "              +              v              );              }                      

Complete Example

                          package              com.codeahoy.ex              ;              import              java.util.Collection              ;              import              java.util.HashMap              ;              import              java.util.Map              ;              import              java.util.Set              ;              public              class              MapExample              {              public              static              void              main              (              String              []              args              )              {              // new map              Map              <              Integer              ,              String              >              map              =              new              HashMap              <>();              // add data              map              .              put              (              1              ,              "V1"              );              map              .              put              (              5              ,              "V2"              );              map              .              put              (              10              ,              "V3"              );              System              .              out              .              println              (              "#1. Using forEach"              );              map              .              forEach              (              (              k              ,              v              )              ->              {              System              .              out              .              println              (              "key: "              +              k              +              ", value: "              +              v              );              });              System              .              out              .              println              (              "#2. Using Map.entrySet() method"              );              for              (              Map              .              Entry              <              Integer              ,              String              >              entry              :              map              .              entrySet              ())              {              Integer              k              =              entry              .              getKey              ();              String              v              =              entry              .              getValue              ();              System              .              out              .              println              (              "key: "              +              k              +              ", value: "              +              v              );              }              System              .              out              .              println              (              "#3. Using map.keySet() method - Keys only"              );              Set              <              Integer              >              keys              =              map              .              keySet              ();              for              (              Integer              k              :              keys              )              {              System              .              out              .              println              (              "key: "              +              k              );              }              System              .              out              .              println              (              "#4. Using map.values() method - Values only"              );              Collection              <              String              >              values              =              map              .              values              ();              for              (              String              v              :              values              )              {              System              .              out              .              println              (              "value: "              +              v              );              }              }              }                      

Output:

            #1. Using forEach key: 1, value: V1 key: 5, value: V2 key: 10, value: V3  #2. Using Map.entrySet() method key: 1, value: V1 key: 5, value: V2 key: 10, value: V3  #3. Using map.keySet() method - Keys only key: 1 key: 5 key: 10  #4. Using map.values() method - Values only value: V1 value: V2 value: V3                      

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How to Get Values From Object in Java

Source: https://codeahoy.com/java/How-To-Get-Keys-And-Values-From-Map/

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