What is the difference between a HashSet and HashMap?

HashMap Stores elements in form of key-value pair i.e each element has its corresponding key which is required for its retrieval during iteration. HashSet stores only objects no such key value pairs maintained. Put method of hash map is used to add element in hashmap.

What is the difference between HashSet HashMap and Hashtable?

HashMap and Hashtable stores values in key-value pair. HashSet contains unique elements and HashMap, HashTable contains unique keys.

What is difference between hash and Map?

HashMap is a non-synchronized class of the Java Collection Framework that contains null values and keys, whereas Map is a Java interface, which is used to map key-pair values.

Which is better HashMap or HashSet?

HashMap is faster than HashSet because the values are associated to a unique key. In HashSet , member object is used for calculating hashcode value which can be same for two objects so equals() method is used to check for equality. If it returns false , that means the two objects are different.

What is difference between Set and HashSet?

A Set is a generic set of values with no duplicate elements. A TreeSet is a set where the elements are sorted. A HashSet is a set where the elements are not sorted or ordered.

Is HashSet a hash table?

Hashtable, HashMap and HashSet are woking based on Hash Table data structure. You can use one null key and which kind of null values you want for HashMap but Hashtable does not allow null key or null values.

Why is hash better than Map?

Null Keys : STL Map allows one null key and multiple null values whereas hash table doesn’t allow any null key or value. Thread synchronization : Map is generally preferred over hash table if thread synchronization is not needed. Hash table is synchronized.

Why is HashMap faster?

The reason that HashMap is faster than HashSet is that the HashMap uses the unique keys to access the values. It stores each value with a corresponding key and we can retrieve these values faster using keys during iteration. While HashSet is completely based on objects and therefore retrieval of values is slower.

Why null key is allowed in HashMap?

For HashMap, it allows one null key and there is a null check for keys, if the key is null then that element will be stored in a zero location in Entry array. We cannot have more than one Null key in HashMap because Keys are unique therefor only one Null key and many Null values are allowed.

Can HashMap have duplicate keys?

HashMap stores key, value pairs and it does not allow duplicate keys. If the key is duplicate then the old key is replaced with the new value.