Collections

how to create a HashSet using Collections in java
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In this example we shall see how can we create  a HashSet using collections class.

For creating a HashSet we have to import the java.util package in which the HashSet class is defined. In this example we have created a class name CollectionExample in which we created a HashSet and added various elements to it.
 In this example have used the default constructor of the HashSet for creating an object of the HashSet. This constructor have this following syntax,

HashSet()
This default constructor constructs a new, empty HashSet havint the initial capacity (16) and load factor (0.75).

For adding the objects to the HashSet we use the add() method defined in the java.util.Collections class.
The add() method has the following syntax:
boolean add(Object obj)

The above method adds the element  to the HashSet if the element is not already present in the HashSet. That means, a HashSet does not contains the duplicate elements, since it is a subclass of Set class.
 

In the following example we have created an object of the HashSet class. By using the generics we have created an Integer type HashSet whose object is set. Currently the set does not contains any elements in it. so we have added some elements to it by using the add(Object obj) method on the HashSet object i.e set. Finally, we have displayed the elements of the HashSet set.

The HashSet is created by the following statement in the given example,
HashSet<Integer> set=new HashSet<Integer>();

 
package r4r.co.in;
package r4r.co.in;
import java.util.*;


public class CollectionExample
{

/**
* @param args
*/
public static void main(String[] args)
{
// TODO Auto-generated method stub
HashSet<Integer> set=new HashSet<Integer>(); // creating a HashSet named set
set.add(1); // adding elements to the set
set.add(3);
set.add(4);
set.add(5);
set.add(7);
set.add(1);
set.add(4);
set.add(7);
System.out.println("The contents of the set are:");
System.out.println(set); // displaying the contents of the set

}


}
The output of the above code is as follows:

The contents of the set are:
[1, 3, 4, 5, 7]
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