In this article, we will discuss how to reverse the contents of LinkedHashSet
Key points about LinkedList:
- LinkedHashSet maintains insertion-order
- It uses doubly-linked list and hashtable to store element/objects
To reverse LinkedHashSet contents:
- We can iterate through LinkedHashSet in reverse order
- By converting LinkedHashSet into ArrayList and using Collections class’ reverse() method
- Method signature: public static void reverse(List list);
- This method is used to reverse the order of ArrayList contents i.e.; reverse-order of insertion-order
ReverseLinkedHashSetContents.java
package in.bench.resources.java.collections;
import java.util.ArrayList;
import java.util.LinkedHashSet;
import java.util.Collections;
public class ReverseLinkedHashSetContents {
public static void main(String[] args) {
// creating LinkedHashSet object of type String
LinkedHashSet<String> lhsCompanies =
new LinkedHashSet<String>();
// adding elements to LinkedHashSet object
lhsCompanies.add("LinkedIn");
lhsCompanies.add("Amazon");
lhsCompanies.add("Google");
lhsCompanies.add("Apple");
lhsCompanies.add("Facebook");
lhsCompanies.add("Oracle");
lhsCompanies.add("Microsoft");
// Iterating using enhanced for-loop
System.out.println("Insertion Order: Iterating LinkedHashSet\n");
for(String company : lhsCompanies) {
System.out.println(company);
}
// convert to ArrayList
ArrayList<String> alCompanies =
new ArrayList<String>(lhsCompanies);
// to reverse LinkedHashSet contents
Collections.reverse(alCompanies);
// reverse order of LinkedHashSet contents
System.out.println("\n\n\nReverse Order of LinkedHashSet\n");
for(String company : alCompanies) {
System.out.println(company);
}
}
}
Output:
Insertion Order: Iterating LinkedHashSet
LinkedIn
Amazon
Google
Apple
Facebook
Oracle
Microsoft
Reverse Order of LinkedHashSet
Microsoft
Oracle
Facebook
Apple
Google
Amazon
LinkedIn
From above example, LinkedHashSet
- doesn’t allow duplicate elements
- maximum of one null object is allowed
- while iterating, maintains insertion-order
References:
- https://docs.oracle.com/javase/tutorial/collections/intro/
- https://docs.oracle.com/javase/tutorial/collections/interfaces/collection.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Collection.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Iterator.html
- https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
- https://docs.oracle.com/javase/7/docs/api/java/util/Set.html
- https://docs.oracle.com/javase/7/docs/api/java/util/class-use/HashSet.html
- https://docs.oracle.com/javase/7/docs/api/java/util/HashSet.html
- https://docs.oracle.com/javase/7/docs/api/java/util/LinkedHashSet.html
- http://docs.oracle.com/javase/7/docs/api/index.html?java/util/class-use/LinkedHashSet.html
Happy Coding !!
Happy Learning !!
