Are they AVL trees, red-black trees, or something else?
Red-black trees as described in the first line of the javadoc.
Tree Map
Tree Set
From the java.util.TreeMap<K,V> documentation:
A Red-Black tree based NavigableMap implementation.
For questions like these, you should always first consult the documentation. The API shouldn't describe ALL of the inner-workings of a class, but elementary informations such as general data structures and algorithms used are usually documented.
Other Java Collections Framework trivias
These are all little trivias that are also clearly documented:
TreeSet is implemented with a TreeMap
HashSet is implemented with a HashMap
Collections.sort uses modified mergesort
Map<K,V> is not a Collection<?>
ArrayList doesn't specify exact growth policy (unlike, say, Vector)
Related questions
Why does java.util.Arrays.sort(Object[]) use 2 kinds of sorting algorithms?
Why does the Java Collections Framework offer two different ways to sort?
Why doesn't Java Map extends Collection?
The first sentence of the TreeMap Javadoc states:
A Red-Black tree based NavigableMap implementation.
It is a red-black tree in the Oracle desktop Java implementation, but an AVL-tree in Android.
TreeSet is based on TreeMap.
And they uses red-black tree, red-black tree is a kind of AVL.
Related
I came across the below in the JAVA docs related to the LinkedHashSet:
Hash table and linked list implementation of the Set interface, with predictable iteration order.
But If I see the source of LinkedHashSet I am not able to find any implements/extends related to HashTable or LinkedList. Then how does it inhibits the features of both these data structures?
It does not inherit from those classes, or use them in any way.
But you could write your own linked list class, and it would still be a linked list, even if it had no relationship to java.util.LinkedList. That's how LinkedHashSet works: it does not use java.util.Hashtable, nor java.util.LinkedList, but it has an implementation of the data structures nonetheless.
Does the standard Java SDK have a class that represents a Self Balancing Binary Search Trees out of the box?
TreeMap and TreeSet (suppose it just uses TreeMap under the hood)
TreeMap implements NavigableMap interface and bases it’s internal working on the principles of red-black trees
I want to keep the ordering and allow duplicates. Should I build one for myself? Or is there some way that I can tweak Comparator (which I think remove() and insert() are using the same)? Thanks.
I want remove() to be in O(log n) and add() to be O(log n) as well.
PriorityQueue is one way but its remove() method takes O(n). If possible, how could I tweak this?
Can you see TreeBag of Apache Commons-Collections? This use a TreeMap to provide the data storage, which provides provides guaranteed log(n) time cost for the containsKey, get, put and remove operations.
A Bag stores each object in the collection together with a count of occurrences.
Guava's TreeMultiset, perhaps? Unlike Apache Commons, TreeMultiset and the other Multisets get along with generics and properly obey the Collection contract, which makes it somewhat friendlier to use.
(Disclosure: I contribute to Guava.)
I am using the Java Tree from collection but what will be the actual use of Tree.
As in CS language, a B-tree can have a max of 2 childs , leaf , height of the tree and other.
But in java how these interpretation can be observed and what is the implementation of Tree in java.
I am talking about TreeMap and TreeSet only
If you are talking about the TreeSet and TreeMap classes, they are implementing the Set and Map interfaces respectively with an internal representation of a Tree structure. So the tree inside is not accessible to users (you cannot access the children directly)
Note: there is no standard Tree interface in java
There isn't a Tree - are you sure you don't mean either TreeSet or TreeMap?
Either way, both of these use Red-Black Trees as the underlying implementation.
Apart from having the performance characteristics of Red-Black trees ( O(log(n)) time for most common operations), they otherwise behave in pretty much the same way as HashSet and HashMap - in most cases you can use them interchangeably.
Can any one please guide me to look in depth about the Data Structures used and how is it implemented in the List, Set and Maps of Util Collection page.
In Interviews most of the questions will be on the Algorithms, but I never saw anywhere the implementation details, Can any one please share the information.
To learn how Java implements collections, the definitive place to go is the source code itself, freely available. Generally, Lists are implemented as either arrays (ArrayList) or linked lists (LinkedList); sets are either hashtables (HashSet) or trees (TreeSet); and maps are hashtables (HashMap).
Algorithms for manipulating arrays, linked lists, hashtables, and binary or n-ary trees (add, remove, search, sort) are complex enough in themselves that an entire course is necessary to cover them all. Anyone doing their own program design typically needs to understand these algorithms and their performance tradeoffs by heart. There's no substitute here for textbook study and/or practice.
The source code of the API is available, get a JDK and open up the src.zip file from the installation folder.
ArrayList: array
LinkedList: doubly linked list (Entry objects)
HashMap: array of Entry objects each Entry pointing to singly linked list
HashSet: internally uses HashMap, stores data as Key and dummy Object (of class Object) as Value in the map.
TreeMap: Red-Black tree implementation of Entry objects.
TreeSet: internally uses TreeMap. Key as data and dummy object as value.
*Entry: is an internal class in these collections and generally has Key, Value, references for other Entry objects etc.
You can always open the source files, it's all there, however, I wouldn't recommend it as usually they are quite hard to understand. Instead, I'd try finding the underlying data structure, and looking it up. Wikipedia contains most of the information you want to know on these subjects, and google contains the absolute rest.
List is just a dynamic array,
Set is a... set,
And maps are usually hash tables keyed by the key's hash, and stored as key-value pair.
If you're going to dive into the source code, I'd recommend familiarizing yourself with "how-it-probably-works", cause otherwise it will be hard to understand, especially the hash table.