What is the use of EnumMap in Java?
Methods of Java EnumMap class It is used to copy the mapped value of one map to another map. It is used to check whether a specified key is present in this map or not. It is used to check whether one or more key is associated with a given value or not.
Can we use enumeration with HashMap?
Enumeration enumeration = new IteratorEnumeration(hashMap. keySet(). It is easy – just make an implementation of Enumeration , pass the Iterator in a constructor, and whenever hasMoreElements() and nextElement() are called, you call the hasNext() and next() on the underlying Iterator .
Why do we use WeakHashMap in Java?
WeakHashMap is an implementation of the Map interface that stores only weak references to its keys. Storing only weak references allows a key-value pair to be garbage-collected when its key is no longer referenced outside of the WeakHashMap. This class provides the easiest way to harness the power of weak references.
What is EnumSet and EnumMap in Java?
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. EnumMap doesn’t allow to insert the null keys, however, null values can be inserted.
Is EnumMap ordered?
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 constant are declared inside enum type ) It’s a high-performance map implementation, much faster than HashMap.
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.
Can we use enum as key in HashMap Java?
In HashMap, there is no constraint. You can use Enum as well as any other Object as key.
What is the difference between HashMap and WeakHashMap in java?
A WeakHashMap has key-value pairs i.e. it is quite similar to a HashMap in Java. A difference is that the WeakHashMap object that is specified as a key is still eligible for garbage collection. This means that the garbage collector has dominance over the WeakHashMap.
Where is WeakHashMap used?
people use it to implement ‘cache memory’. If you have some objects that are reused often in your application, and their construction is expensive, and there are too many of them to keep them all in memory – – you use WeakHashMap.