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HashSet Example

In this section we are discussing HashSet with example code that shows the methods to add, remove and iterate the values of collection.

HashSet Example


In this section we are discussing HashSet with example code that shows the methods to add, remove and iterate the values of collection. A HashSet is a collection set that neither allows duplicate elements nor order or position its elements.

Description of program:

In the following code segment we are performing various operations on HashSet collection. We have explained the steps to add, remove, and test the elements of the collection. Keys are used to put and get values. We can also execute this code on a Vector by changing the HashSet declaration and constructor to a Vector as it supports the collection interface.  

To insert an element in the HashSet collection add() method is used. The size() method helps you in getting the size of the collection. If you want to delete any element, use the remove() method which takes index as parameter. In order to remove all data from the HashSet use clear() method. When the HashSet is empty, our program checks for it and displays a message "Collection is empty". If the collection is not empty then program displays the size of HashSet.

Here is the code of program:

import java.util.*;

public class CollectionTest {
  public static void main(String [] args) { 
  System.out.println"Collection Example!\n" )
  int size;
  // Create a collection  
  HashSet <String>collection = new HashSet <String>();
  String str1 = "Yellow", str2 = "White", str3 = "Green", str4 = "Blue";  
  Iterator iterator;
  //Adding data in the collection
  System.out.print("Collection data: ");  
  //Create a iterator
  iterator = collection.iterator()
  while (iterator.hasNext()){
  System.out.print( " ");  
  // Get size of a collection
  size = collection.size();
  if (collection.isEmpty()){
  System.out.println("Collection is empty");
  System.out.println"Collection size: " + size);
  // Remove specific data  
  System.out.println("After removing [" + str2 + "]\n");
  System.out.print("Now collection data: ");
  iterator = collection.iterator()
  while (iterator.hasNext()){
  System.out.print( " ");  
  size = collection.size();
  System.out.println("Collection size: " + size + "\n");
  //Collection empty
  size = collection.size();
  if (collection.isEmpty()){
  System.out.println("Collection is empty");
  System.out.println"Collection size: " + size);

Download this example.

Output of this program:


C:\vinod\collection>java CollectionTest
Collection Example!

Collection data: Blue White Green Yellow
Collection size: 4

After removing [White]

Now collection data: Blue Green Yellow
Collection size: 3

Collection is empty



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  Reload Image
April 9, 2011

eay to understand
September 23, 2011

very nice example
October 18, 2011
Program to the interface

You should always program to the interface. This is wrong: HashSet <String>collection = new HashSet <String>(); It should be this: Set <String> collection = new HashSet <String>();
Ali Harb
December 13, 2011
return value of the add method

The add method specifies that a boolean should be returned but in the code we do not assign "collection.add(str1)" to anything. Why is this allowed?
May 6, 2012
Doubt regarding the above code...

can any one tell after inserting blue,green,yellow etc how can i retreive only green from the hashset..???
M a Hossan
June 16, 2012
Want to know the exPlation

You did use very good exmple could you explain it that how the blue is printed frist if you know place. Send the answer in my email