Java Hashset class implements Set interface. It has the following properties.
1. HashSet does not allow duplicates, means it contains unique elements.
2. HashSet is unordered meaning it does not guarantee that the order will remain constant over time.
3. HashSet is backed by Hashtable (actually a HashMap instance).
4. HashSet permits the null elements.
5. HashSet implementation is not synchronized. It can be synchronized externally.
Set s = Collections.synchronizedSet(new HashSet(...));
6. Iterators returned by HashSet class is fail- fast.
HashSet Example
import java.util.*;
public class HashSetExample {
public static void main(String args[]) {
// Declare HashSet
HashSetString> hashset =
new HashSetString>();
// Adding elements to the HashSet
hashset.add("Apple");
hashset.add("Pear");
hashset.add("Mango");
hashset.add("Papaya");
hashset.add("Orange");
//Addition of duplicate elements
hashset.add("Apple");
hashset.add("Mango");
//Addition of null values
hashset.add(null);
hashset.add(null);
//Displaying HashSet elements
System.out.println(hashset);
}
}
Output :
[null, Apple, Pear, Papaya, Mango, Orange]
HashSet Methods
1. boolean add(Element e) : it adds the element e to the list.2. public void clear() : it removes all of the elements from the set.
3. public Object clone() : It returns the shallow copy of the HashSet instance.
4. public boolean contains(Object o) : it returns true if the set contains the specified element.
5. public boolean isEmpty() : This method returns true if the set contains no elements.
6. public boolean remove(Object o) : it removes the specified element from the set if it is present.
7. public int size() : it returns the number of elements in the set.
HashSet Tutorials
Basics
Conversions
Differences
More Interview Questions
References : HashSet Oracle docs
