linkedhashset

Consider the following SSCCE: public static void main(String[] args) { LinkedHashSet<String> set1 = new LinkedHashSet<>(); set1.add("Bob"); set1.add("Tom"); set1.add("Sam"); LinkedHashSet<String> set2 = new LinkedHashSet<>(); set2.add("Sam"); set2.add("Bob"); set2.add("Tom"); System.out.println(set1); System.out.println(set2); System.out.println(set1.equals(set2)); } This prints: [Bob, Tom, Sam] [Sam, Bob, Tom] true Yet if you change LinkedHashSet to LinkedList : public static void main(String[] args) { LinkedList<String> set1 = new LinkedList<>(); set1.add("Bob"); set1.add("Tom"); set1.add(

I need a collection that keeps insertion order and has unique values. LinkedHashSet looks like the way to go, but there's one problem - when two items are equal, it removes the newest one (which makes sense), here's an example: set.add("one"); set.add("two"); set.add("three"); set.add("two"); The LinkedHashSet will print: one , two , three But what I need is: one , three , two What would be the best solution here? Is there any collection/collections method that can do this or should I implement it manually? Most of the Java Collections can be extended for tweaking. Subclass LinkedHashSet ,

I just understand that LinkedHashSet does not allows duplicate elements when it is inserting. But, I dont understand how does Hashset works in Hava? I know a bit that Hashtable is used in Hashset so the hashtable used to store the elements and here also does not allow the duplicate elements. Then, Treeset is also similar to Hashset it also does not allows duplicate entries so unique elements will be seen and it follows ascending order. I have one more doubt regarding HashMap - Hashmap does not maintains order. It may have one null key and multiple null values. I just dont understand this and

How can I iterate through items of a LinkedHashSet from the last item to the first one? Jeffrey If you want to continue to use collections, you could use the following: LinkedHashSet<T> set = ... LinkedList<T> list = new LinkedList<>(set); Iterator<T> itr = list.descendingIterator(); while(itr.hasNext()) { T item = itr.next(); // do something } If you're fine with using an array instead, you could take a look at hvgotcodes' answer . hvgotcodes er, assuming you mean LinkedHashSet... I would use toArray and just use a reverse for loop. There might be a better way to do it, but that should work.

Why do the second and third sets preserve order: Integer[] j = new Integer[]{3,4,5,6,7,8,9}; LinkedHashSet<Integer> i = new LinkedHashSet<Integer>(); Collections.addAll(i,j); System.out.println(i); HashSet<Integer> hi = new HashSet<Integer>(i); System.out.println(hi); LinkedHashSet<Integer> o = new LinkedHashSet<Integer>(hi); System.out.println(o); Here's the output I get: 3,4,5,6,7,8,9 3,4,5,6,7,8,9 3,4,5,6,7,8,9 Behrang The second one (just using HashSet ) is only a coincidence. From the JavaDocs : This class implements the Set interface, backed by a hash table (actually a HashMap instance).

What is the difference between them? I know that A LinkedHashSet is an ordered version of HashSet that maintains a doubly-linked List across all elements. Use this class instead of HashSet when you care about the iteration order. When you iterate through a HashSet the order is unpredictable, while a LinkedHashSet lets you iterate through the elements in the order in which they were inserted. But in sourcecode of LinkedHashSet there are only calling constructors of HashSet. So where is double-linked List and insertion order? The answer lies in which constructors the LinkedHashSet uses to