The Set interface of the Java Collections framework provides the features of the mathematical set in Java. It extends the Collection interface.
Unlike the List interface, sets cannot contain duplicate elements.
Since Set is an interface, we cannot create objects from it.
In order to use functionalities of the Set interface, we can use these classes:
In Java, we must import java.util.Set package in order to use Set.
// Set implementation using HashSet Set<string> animals = new HashSet<>()
Here, we have created a Set called animals. We have used the HashSet class to implement the Set interface.
Methods of Set:
The Set interface includes all the methods of the Collection interface. It’s because Collection is a super interface of Set.
Some of the commonly used methods of the Collection interface that’s also available in the Set interface are:
To learn about more methods of the Setinterface, visit Java Set (official Java documentation).
The LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. When the iteration order is needed to be maintained this class is used. When iterating through a HashSet the order is unpredictable, while a LinkedHashSet lets us iterate through the elements in the order in which they were inserted. When cycling through LinkedHashSet using an iterator, the elements will be returned in the order in which they were inserted.
Given an integer array A you need to find the total number of unique elements in that array A.
1 <= |A| <= 105
1 <= A[i] <= 109
The first-line contain a single integer N denoting the size of the array A.
Next N lines each contain a single integer denoting the array A elements.
Print a single integer denoting the total number of unique elements in that array A.
5 1 1 3 1 2
Unique elements are : [1, 2, 3]