What is EnumSet in Java?
An EnumSet is a specialized Set collection to work with enum classes. It implements the Set interface and extends from AbstractSet: Even though AbstractSet and AbstractCollection provide implementations for almost all the methods of the Set and Collection interfaces, EnumSet overrides most of them.
How do you declare an EnumSet?
It extends AbstractSet class and implements Set Interface in Java. EnumSet class is a member of the Java Collections Framework & is not synchronized….Methods of EnumSet.
Method | Action Performed |
---|---|
of(E e1, E e2) | Creates an enum set initially containing the specified elements. |
How do you create an empty EnumSet in Java?
Use EnumSet. noneOf(Class) to create an empty EnumSet.
What is enum map?
EnumMap is a specialized implementation of the Map interface for enumeration types. It extends AbstractMap and implements the Map interface in Java. It belongs to java. util package.
How and when would you use the enum collection?
You should use enum types any time you need to represent a fixed set of constants. That includes natural enum types such as the planets in our solar system and data sets where you know all possible values at compile time—for example, the choices on a menu, command line flags, and so on.
What is EnumSet noneOf?
noneOf(Class elementType) method creates an empty enum set with the specified element type.
What is EnumMap and EnumSet?
EnumMap is a specialized implementation of the Map interface for the enumeration types. EnumSet is a specialized implementation of the Set interface for the enumeration types. EnumMap is internally represented as an array. EnumSet is internally represented as a BitVector.
What is the use of EnumMap?
Can we use enum as map?
EnumMap is an ordered collection and they are maintained in the natural order of their keys(the natural order of keys means the order on which enum constants are declared inside enum type ) It’s a high-performance map implementation, much faster than HashMap.
Can we use enum as map key?
In HashMap, there is no constraint. You can use Enum as well as any other Object as key.
Why enums are used in Java?
Enums are used when we know all possible values at compile-time, such as choices on a menu, rounding modes, command-line flags, etc. It is not necessary that the set of constants in an enum type stay fixed for all time. In Java (from 1.5), enums are represented using enum data type.
Is EnumSet ordered?
By default Enums declaration order defines the natural ordering of the Enums. From javadoc of compareTo: Enum constants are only comparable to other enum constants of the same enum type. The natural order implemented by this method is the order in which the constants are declared.
Why is EnumMap faster than HashMap?
EnumMap is much faster than HashMap. All keys of each EnumMap instance must be keys of the same enum type. EnumMap doesn’t allow inserting null key if we try to insert the null key, it will throw NullPointerException. EnumMap is internally represented as arrays therefore it gives the better performance.
Can we use enum in map key?
How do I create an enum map?
Constructors of EnumMap
- EnumMap(Class keyType): The constructor is used to create an empty EnumMap with the specified keyType.
- EnumMap(EnumMap m): The constructor is used to create an enum map with the same keyType as the specified enum map, with initial mappings being the same as the EnumMap.
Can you map an enum?
To use the map() method with enums: Use the Object. keys() method to get an array of the enum’s keys. Use the map() method to iterate over the array.
Can enum be used in HashMap?
In HashMap, we can use Enum as well as any other object as a key. It doesn’t allow storing null key. It allows to store the null keys as well values, but there should be only one null key object and there can be any number of null values. HashMap internally uses the HashTable.
Why is enum required?
Enums are lists of constants. When you need a predefined list of values which do represent some kind of numeric or textual data, you should use an enum. You should always use enums when a variable (especially a method parameter) can only take one out of a small set of possible values.
Should you use enums in Java?
What is difference between map and EnumMap?
EnumMap: EnumMap is a specialized implementation of the Map interface for enumeration types. It extends AbstractMap and implements the Map interface in Java….Difference between EnumMap and HashMap.
EnumMap | HashMap |
---|---|
EnumMap is a specialized map implementation that uses only Enum type key. | In HashMap, we can use Enum as well as any other object as a key. |