EnumMap class in Java with Example

2

EnumMap is specialized implementation of Map interface for enumeration types.
It extends AbstractMap and implements Map Interface in Java. It is a generic class declared as:
Syntax:

public class EnumMap<K extends Enum<K>,V>
K: specifies the keys
V: specifies values

K must extend Enum, which enforces the requirement that the keys must be of specified enum type.

Important points:

  • EnumMap class is a member of the Java Collections Framework & is not synchronized.
  • EnumMap is ordered collection and they are maintained in the natural order of their keys( natural order of keys means the order on which enum constant are declared inside enum type )
  • It’s a high performance map implementation, much faster than HashMap.
  • All keys of each EnumMap instance must be keys of a single enum type.
  • EnumMap doesn’t allow null key and throw NullPointerException, at same time null values are permitted.
// Java program to illustrate working of EnumMap and
// its functions.
import java.util.EnumMap;

public class Example
{
    public enum GFG
    {
        CODE, CONTRIBUTE, QUIZ, MCQ;
    }

    public static void main(String args[]) 
    {    
        // Java EnumMap Example 1: creating EnumMap in java with key 
        //as enum type STATE
        EnumMap<GFG, String> gfgMap = new EnumMap<GFG, String>(GFG.class);

        // Java EnumMap Example 2:
        // putting values inside EnumMap in Java
        // we are inserting Enum keys on different order than their natural order
        gfgMap.put(GFG.CODE, "Start Coding with gfg");
        gfgMap.put(GFG.CONTRIBUTE, "Contribute for others");
        gfgMap.put(GFG.QUIZ, "Practice Quizes");
        gfgMap.put(GFG.MCQ, "Test Speed with Mcqs");
        
        // printing size of EnumMap in java
        System.out.println("Size of EnumMap in java: " + gfgMap.size());
     
        // printing Java EnumMap , should print EnumMap in natural order
        // of enum keys (order on which they are declared)
        System.out.println("EnumMap: " + gfgMap);
     
        // retrieving value from EnumMap in java
        System.out.println("Key : " + GFG.CODE +" Value: " 
                            + gfgMap.get(GFG.CODE));
     
        // checking if EnumMap contains a particular key
        System.out.println("Does gfgMap has :" + GFG.CONTRIBUTE + " : "
                            +  gfgMap.containsKey(GFG.CONTRIBUTE));
     
        // checking if EnumMap contains a particular value
        System.out.println("Does gfgMap has :" + GFG.QUIZ + " : " 
                            + gfgMap.containsValue("Practice Quizes"));
        System.out.println("Does gfgMap has :" + GFG.QUIZ + " : " 
                            + gfgMap.containsValue(null));
    }
}

Output:


Size of EnumMap in java: 4
EnumMap: {CODE=Start Coding with gfg, CONTRIBUTE=Contribute for others, QUIZ=Practice Quizes
,MCQ=Test Speed with Mcqs}
Key : CODE Value: Start Coding with gfg
Does gfgMap has :CONTRIBUTE : true
Does gfgMap has :QUIZ : true
Does gfgMap has :QUIZ : false

Methods

  • put(K key, V value) : Associates the specified value with the specified key in this map.
  • size() : Returns the number of key-value mappings in this map.
  • get(Object key) : Returns the value to which the specified key is mapped, or null if this map contains no mapping for the key.
  • containsKey(Object key) : Returns true if this map contains a mapping for the specified key.
  • containsValue(Object value) : Returns true if this map maps one or more keys to the specified value.

Please refer below reference for full list of methods of this class
https://docs.oracle.com/javase/7/docs/api/java/util/EnumMap.html

This article is contributed by Pratik Agarwal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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