HashSet in java

In this previous post, we have seen how to Iterate over a Vector. In this post, we will learn about HashSet in java.

HashSet has the following features.

• HashSet implements Set interface.
• It does not maintain any insertion order. Elements would be returned in any random order.
• Allows only unique value. If we try to add duplicate elements, then old value will be overwritten.
• HashSet is non-synchronized.
• HashSet allows null values however if you insert more than one nulls it would still return only one null value.

Syntax:

HashSet<ObjectType> name = new HashSet<ObjectType>();

Example:

import java.util.HashSet;

public class HashSetExample {

	public static void main(String[] args) {
		
		HashSet<String> cars = new HashSet<String>();
		cars.add("BMW");
		cars.add("Honda");
		cars.add("Ferrari");
		cars.add("Bugatti");
		cars.add("Mercedes");
		
		//Add duplicate elements
		cars.add("Ferrari");
		cars.add("BMW");
		
		//Addition of null values
		cars.add(null);
		cars.add(null);
		
		
		//Display the hashset
		System.out.println("HashSet : "+cars);
	}

}

Output:

HashSet : [null, Bugatti, BMW, Ferrari, Honda, Mercedes]

HashSet Methods:

• boolean add(Element  e): It adds the element e to the HashSet.
• void clear(): It removes all the elements from the Set.
• Object clone(): This method returns a shallow copy of the HashSet.
• boolean contains(Object o): It checks whether the specified Object o is present in the list or not. If the object has been found it returns true else false.
• boolean isEmpty(): Returns true if there is no element present in the Set.
• int size(): It gives the number of elements of a Set.
• boolean remove(Object o): It removes the specified Object o from the Set.