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EnumMap in Java




Java Java Map

EnumMap in Java

EnumMap in Java is a specialized class that implements the Map interface for enum data types. It belongs to the java.util package. It maintains natural sorting order on the basis of the keys in the map.

Features of EnumMap

  • It is an ordered collection of elements of enum data type
  • Not synchronized
  • Performance is higher than HashMap
  • All keys are an instance of elements in the Enum data type
  • We cannot store null keys in an EnumMap class.
  • EnumMap stores data internally in the form of arrays hence it is more efficient.

Java EnumMap hierarchy

EnumMap in Java

EnumMap Constructors

ConstructorDescription
EnumMap(Class keyType)Creates an EnumMap with the specified keytype
EnumMap(EnumMap m)Creates an EnumMap with the specified keys in the enummap
EnumMap(Map m)Create an EnumMap with the specified map

Methods

MethodDescriptionParameter
void clear()Removes all the mappings in this map which means map will be empty
Boolean containsKey(Object key)Returns true if there is a mapping value for the specified keykey - the key for which we need to retrieve the value
Boolean containsValue(Object value)Returns true if there is mapping of key for the specified valuevalue - the value for which specified key is mapped
Set<Entry> entrySet()Returns a set view of the mapping of the map
Boolean equals(Object o)Returns true if the object has the same mapping of the mapo - the object to be compared
Integer get(Object key)Returns the value of the specified key in the map. It returns null if there is no mappingkey - the key for which value mapping has to be retrieved
Integer getOrDefault(Object key, Integer defaultvalue)Returns the value of the specified key if mapped, else returns the defaultvalue if there is no mappingkey - the key for which we value has to be returned
defaultvalue - the default value to be returned when there is no mapping
int hashCode()Returns the hashcode value of the map
Boolean isEmpty()Returns true is the map does not have any key-value pairs
Set keySet()Returns the set view of the keys present in the map
Integer put(String key, int value)Associates the key with value. If the key is already present, it replaces the old value with new valuekey - key for mapping
value - value for the specified key
void putAll(Map m)Associates all key - value mappings of m to the current mapm - the copies of the mapping to be added to the current map
Integer putIfAbsent(String key,Integer value)Associates the value if already not mapped to the key else returns the current valuekey - key for mapping
value - value to be associated
Integer remove(Object key)Removes the mapping for the specified key in the mapkey - the key in the map for which mapping has to be removed
Boolean remove(Object key, Object value)Removes the entry of the specified key only if it is mapped with the specified valuekey - key in map
value - value mapped to the key
Integer replace(String key, Integer value)Replaces the value of the specified key with the value only if it currently mapped with some valuekey - key in map
value - value to be replaced
Boolean replace(String key, integer oldvalue, Integer newvalue)Replaces the entry of the specified key with new value only if it already mapped with the specified oldvaluekey - key in the map
oldvalue - oldvalue mapped to key
newvalue - newvalue to be mapped to the key
int size()Returns the size of the map
String toString()Returns a string representation of the map
Collection values()Returns a collection view of values present in the map
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Example: Add elements to EnumMap

Below is an example of adding enum elements to the Java EnumMap using the put() and putAll() methods.

import java.util.EnumMap;

enum Weight {
  UNDERWEIGHT, NORMAL, OVERWEIGHT
}
public class EnumMapDemo {

  public static void main(String[] args) {
    EnumMap<Weight, Integer> e = new EnumMap<Weight, Integer>(Weight.class);
    e.put(Weight.UNDERWEIGHT, 10);
    e.put(Weight.NORMAL, 50);
    
    System.out.println("Size of EnumMap: " + e.size());
    System.out.println("Values in EnumMap" + e);
    
    EnumMap<Weight, Integer> e2 = new EnumMap<Weight, Integer>(Weight.class);
    e2.put(Weight.OVERWEIGHT, 100);
    
    e.putAll(e2);
    System.out.println("Values in EnumMap after putAll: " + e);
    
  }

}
Size of EnumMap: 2
Values in EnumMap{UNDERWEIGHT=10, NORMAL=50}
Values in EnumMap after putAll: {UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=100}

Example: Replace elements

The below example illustrates how to replace values in an EnumMap using the replace() method.

import java.util.EnumMap;

enum Weight {
  UNDERWEIGHT, NORMAL, OVERWEIGHT
}
public class EnumMapDemo {

  public static void main(String[] args) {
    EnumMap<Weight, Integer> e = new EnumMap<Weight, Integer>(Weight.class);
    e.put(Weight.UNDERWEIGHT, 10);
    e.put(Weight.NORMAL, 50);
    e.put(Weight.OVERWEIGHT, 80);
    
    System.out.println("Values in EnumMap" + e);
        
    e.replace(Weight.UNDERWEIGHT, 30);
    e.replace(Weight.NORMAL, 50, 55);
    
    System.out.println("Values after replace method: " + e);
  }

}
Values in EnumMap{UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=80}
Values after replace method: {UNDERWEIGHT=30, NORMAL=55, OVERWEIGHT=80}

Example: Delete elements

We can delete the elements in a Java EnumMap using the remove() method. The below example shows how to delete a specific element.

import java.util.EnumMap;

enum Weight {
  UNDERWEIGHT, NORMAL, OVERWEIGHT
}
public class EnumMapDemo {

  public static void main(String[] args) {
    EnumMap<Weight, Integer> e = new EnumMap<Weight, Integer>(Weight.class);
    e.put(Weight.UNDERWEIGHT, 10);
    e.put(Weight.NORMAL, 50);
    e.put(Weight.OVERWEIGHT, 80);
    
    System.out.println("Values in EnumMap" + e);		
    
    e.remove(Weight.NORMAL);
    e.remove(Weight.UNDERWEIGHT, 10);
    
    System.out.println("Values in EnumMap" + e);
    
  }

}
Values in EnumMap{UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=80}
Values in EnumMap{OVERWEIGHT=80}

Example: Access elements of Java EnumMap

Below is an example to access the data in the EnumMap using the get method. We can also check if the map contains a specific key or value using the containsKey or containsValue method.

import java.util.EnumMap;

enum Weight {
  UNDERWEIGHT, NORMAL, OVERWEIGHT
}
public class EnumMapDemo {

  public static void main(String[] args) {
    EnumMap<Weight, Integer> e = new EnumMap<Weight, Integer>(Weight.class);
    e.put(Weight.UNDERWEIGHT, 10);
    e.put(Weight.NORMAL, 50);
    e.put(Weight.OVERWEIGHT, 80);
    
    System.out.println("Values in EnumMap" + e);
        
    System.out.println(e.get(Weight.UNDERWEIGHT));
    System.out.println(e.containsKey(Weight.OVERWEIGHT));
    System.out.println(e.containsValue(50));
    
  }

}
Values in EnumMap{UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=80}
10
true
true

Example: Iterate through EnumMap elements

Similar to Map, we can iterate through an EnumMap using the entrySet method. To retrieve only keys, we can use the keySet method, and to retrieve only the values, we can use the Values method of the Collection.

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The below example illustrates how to iterate using all three methods.

import java.util.EnumMap;

enum Weight {
  UNDERWEIGHT, NORMAL, OVERWEIGHT
}
public class EnumMapDemo {

  public static void main(String[] args) {
    EnumMap<Weight, Integer> e = new EnumMap<Weight, Integer>(Weight.class);
    e.put(Weight.UNDERWEIGHT, 10);
    e.put(Weight.NORMAL, 50);
    e.put(Weight.OVERWEIGHT, 80);
    
    System.out.println("Values in EnumMap" + e);
    
    //Using entrySet
    System.out.println("Iterate using entrySet: " + e.entrySet());
    
    //Using keySet
    System.out.println("Iterate using keySet:");
    for(Weight str : e.keySet())
      System.out.println(str);
    
    //Using Values
    System.out.println("Iterate using Values:");
    for(Integer val: e.values())
      System.out.println(val);
    
  }

}
Values in EnumMap{UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=80}
Iterate using entrySet: [UNDERWEIGHT=10, NORMAL=50, OVERWEIGHT=80]
Iterate using keySet:
UNDERWEIGHT
NORMAL
OVERWEIGHT
Iterate using Values:
10
50
80

 

Reference

Array Interview Questions
Graph Interview Questions
LinkedList Interview Questions
String Interview Questions
Tree Interview Questions
Core Java Interview Questions

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