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Difference between EnumMap and HashMap in Java
EnumMap is introduced in JDK5. It is designed to use Enum as key in the Map. It is also the implementation of the Map interface. All of the key in the EnumMap should be of the same enum type. In EnumMap , key can’t be null and any it will throw NullPointerException.
As per java docs −
EnumMap internally using as arrays, this representation is extremely compact and efficient.
HashMap is also the implementation of the Map interface. It is used to store the data in Key and Value form. It can contain one null key and multiple null values . In HashMap, keys can’t be a primitive type. Java HashMap implementation provides constant-time performance for the basic operations (get and put), assuming the hash function disperses the elements properly among the buckets.
| Sr. No. | Key | EnumMap | HashMap |
|---|---|---|---|
1 | Basic | A specialized Map implementation for use with enum type keys | HashMap is also the implementation of the Map interface. |
2 | Null Key | It can’t have null key. | It can have one null key and multiple null values |
3 | Performance | All operations execute in constant time therefore it is faster than HashMap | It is slower than HashMap |
4. | Internal Implementation | It uses Array internally | It uses Hashtable internally |
5. | Ordering | EnumMap stores keys in the natural order of their keys | HashMap is not ordered |
Example of EnumMap
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.List;
import java.util.Map;
public class EnumMapExample {
public enum LaptopEnum {
HCL, DELL, IBM
};
public static void main(String[] args) {
// create enum map
EnumMap map = new EnumMap(LaptopEnum.class);
map.put(LaptopEnum.HCL, "100");
map.put(LaptopEnum.DELL, "200");
map.put(LaptopEnum.IBM, "300");
// print the map
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
}
}Example of HashMap
import java.util.ArrayList;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
public class HashMapExample {
public static void main(String[] args) {
// create Hash map
Map map = new HashMap();
map.put("HCL", "100");
map.put("DELL", "200");
map.put("IBM", "300");
// print the map
for (Map.Entry m : map.entrySet()) {
System.out.println(m.getKey() + " " + m.getValue());
}
}
}
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