LinkedHashSet Class in Collection

public class LinkedHashSet<E>
extends HashSet<E>
implements Set<E>, Cloneable, Serializable

Hash table and linked list implementation of the Set interface, with predictable iteration order. This implementation differs from HashSet in that it maintains a doubly-linked list running through all of its entries. This linked list defines the iteration ordering, which is the order in which elements were inserted into the set (insertion-order). Note that insertion order is not affected if an element is re-inserted into the set. (An element e is reinserted into a set s if s.add(e) is invoked when s.contains(e) would return true immediately prior to the invocation.)

This class provides all of the optional Set operations, and permits null elements. Like HashSet, it provides constant-time performance for the basic operations (add, contains and remove), assuming the hash function disperses elements properly among the buckets. Performance is likely to be just slightly below that of HashSet, due to the added expense of maintaining the linked list, with one exception: Iteration over a LinkedHashSet requires time proportional to the size of the set, regardless of its capacity. Iteration over a HashSet is likely to be more expensive, requiring time proportional to its capacity.

A linked hash set has two parameters that affect its performance: initial capacity and load factor. They are defined precisely as for HashSet. Note, however, that the penalty for choosing an excessively high value for initial capacity is less severe for this class than for HashSet, as iteration times for this class are unaffected by capacity.

Note that this implementation is not synchronized. If multiple threads access a linked hash set concurrently, and at least one of the threads modifies the set, it must be synchronized externally. This is typically accomplished by synchronizing on some object that naturally encapsulates the set. If no such object exists, the set should be “wrapped” using the Collections.synchronizedSet method. This is best done at creation time, to prevent accidental unsynchronized access to the set:

Set s = Collections.synchronizedSet(new LinkedHashSet(...));

Constructor Detail:
LinkedHashSet()
Constructs a new, empty linked hash set with the default initial capacity (16) and load factor (0.75).
LinkedHashSet(Collection c)
Constructs a new linked hash set with the same elements as the specified collection. Constructs a new linked hash set with the same elements as the specified collection. The linked hash set is created with an initial capacity sufficient to hold the elements in the specified collection and the default load factor (0.75).
LinkedHashSet(int initialCapacity)
Constructs a new, empty linked hash set with the specified initial capacity and the default load factor (0.75).
LinkedHashSet(int initialCapacity, float loadFactor)
Constructs a new, empty linked hash set with the specified initial capacity and load factor. Constructs a new, empty linked hash set with the specified initial capacity and load factor.
Parameters:
initialCapacity – the initial capacity of the linked hash set
loadFactor – the load factor of the linked hash set

Example:

import java.util.*;

public class LinkedHashSetDemo {

   public static void main(String args[]) {
      // create a hash set
      LinkedHashSet hs = new LinkedHashSet();
      // add elements to the hash set
      hs.add("B");
      hs.add("A");
      hs.add("D");
      hs.add("E");
      hs.add("C");
      hs.add("F");
      System.out.println(hs);
   }
}

output:

Example of LinkedHashSet class with duplicate value:

import java.util.*;

public class LinkedHashSetDemo {

   public static void main(String args[]) {
      // create a hash set
      LinkedHashSet hs = new LinkedHashSet();
      // add elements to the hash set
      hs.add("Dinesh");
      hs.add("Anamika");
      hs.add("Sweety");
      hs.add("Dinesh");
      hs.add("Sweety");
      hs.add("RAJ");
      System.out.println(hs);
   }
}

output: