HashSet Class

HashSet

• The underlying data structure is Hashtable.
• Insertion order is not preserved and it is based on hash code of the objects.
• Duplicate objects are not allowed.
• If we are trying to insert duplicate objects we won’t get compile time error and runtime error add() method simply returns false.
• Heterogeneous objects are allowed.
• Null insertion is possible.(only once)
• Implements Serializable and Cloneable interfaces but not RandomAccess.
• HashSet is best suitable, if our frequent operation is “Search”.

Constructors

1. HashSet h = new HashSet()

Creates an empty HashSet object with default initial value 16 and default fill ratio 0.75

2. HashSet h = new HashSet(int initialcapacity)

3. HashSet h = new HashSet(int initialCapacity, float fillratio)

Here fillratio is 0 or 1.

4. HashSet h = new HashSet(Collection c)

Note

After filling how much ratio new HashSet object will be created , The ratio is called “FillRatio” or “LoadFactor“.

package com.ashok.collections.hashset;

import java.util.HashSet;
/**
 * 
 * @author ashok.mariyala
 *
 */
public class MyHashSet {
   public static void main(String args[]) {
      // HashSet declaration
      HashSet<string> hset = new HashSet<string>();
      // Adding elements to the HashSet
      hset.add("Ashok");
      hset.add("Vinod");
      hset.add("Dillesh");
      hset.add("Thiru");
      hset.add("Naresh");
      System.out.println(hset);
  
   // Addition of duplicate elements
      System.out.println(hset.add("Ashok"));

      System.out.println(hset);
  
      // Addition of null values
      hset.add(null);
      System.out.println(hset.add(null));
  
      // Displaying HashSet elements
      System.out.println(hset);
   }
}

Output

[Thiru, Ashok, Dillesh, Vinod, Naresh]
false
[Thiru, Ashok, Dillesh, Vinod, Naresh]
false
[null, Thiru, Ashok, Dillesh, Vinod, Naresh]