Collection Framework

Collection Framework

 Characteristics of CFW or Advantages?

1. CFW provides high performance to java applications

2. CFW provides adaptability

3. CFW provides Extendibility

4.CFC provides Some data structures like stacks, ques,linkedlist etc…………..

 What is 1D/Single CFW?

It organizes the data either row or column but not both. or data is not organizing in the form of (Key,Value)

1D/single CFW interfaces?

             1.java . util.Collection;

              2.java .util.List;

             3.java.util.Set;

             4.java.util.SortedSet;  

In which package CFW API is available?

                Java.util.*;

What is CFW variable?

 The objects of Collection, List ,Set and SortedSet knowns as CFW variable

What is the diff b/w collection and Collections?

Collection is an interface.Collections is a class.

Which of collection class will not allow duplicate values?

Set of collection class will not allow duplicate values and also SortedSet of collection class

But Collection of collection class and List of collection class allows duplicate values

What are the Limitations of Arrays?

 An array is an indexed collection of fixed number of homogeneous data elements.

The main limitations of Object Arrays are

1) Arrays are fixed in size i.e once we created an array there is no chance of increasing or

decreasing it’s size based on our requirement.

2) Arrays can hold only homogeneous data elements.

Ex:-

Student [] s = new Student [600];

s[0] = new Student;----------valid

s[1] = new Integer(10); X

s[2] = "raju"; X

We can resolve this problem by using object Arrays.

Object [] o = new Object [600];

o[0] = new Student;----------------valid

o[1] = new Integer(10);--------------valid

o[2] = "raju";-----------------valid

i.e By using Object Arrays we can hold heterogeneous data elements.

To resolve the above problems of arrays, Sun people has introduced ‘collections concept’

Collections are grow able in nature i.e based on requirement we can increase or decrease the size.

Collections can hold heterogeneous data elements also.

Every collection class has implemented based on some data structure

Hence for every requirement ready made method support is possible.

We can represent all the elements in some sorting order. We can prevent duplicate object insertion

by default.

 What is difference b/w Arrays and Cs?

Arrays                                                         Cs

1.Arrays are in fixed size                         1.Collections are not fixed in size

2.memoery allocations are not good        2.memory allocations are good                                                    

3.Arrays can only  hold homogeneous            3.Collections can hold heterogeneous data elements                                                      data elements

4.Arrays doesn’t having any data             4.Every collection class has built by using

Strcture implementation                                     some data structure

5.Arrays can hold objects and                    5.collections can hold only objects but

Primitives                                                   not primitives

 What is Collections Frame Work?

It defines group of classes and interfaces which can be used for representing a collection of Objects as single entity.

Java:       Collection Frame Work

                                                                                collection

 

C++:         STL(standard Template Library)                  container

 What are the 7 key Interfaces of collection Frame work?

1.      Collection

2.      List

3.      Set

4.      SortedSet

5.      Queue

6.      Map

7.      Sorted Map

What is a Collection interface?

Ø This interface is the root interface for entire collection framework.

Ø This interface can be used for representing a group of objects as single entity.

Ø This interface defines the most common general methods which can be applicable for any collection object.

Ø There is no concrete class which implements collection interface directly

Ø It allows ordered set of objects.

Ø It displays the data Random order

Ø Retrieve the data only in forward direction

What is  the Difference Between Collection and Collections?

Collection is an interface available in java.util package for representing a group of objects as single entity.

Collections is an utility class available in java.util package and defines several utility methods for collection implemented class object

What is the List interface?

Ø This can be used for representing a group of individual objects as a single entity where insertion order is preserved and duplicate objects allowed.

Ø This is child interface of collection.

Ø The following classes implemented List interface directly.

Array List, Linked List, Vector and Stack

Ø It displays the data sequential order

       

Ø Retrieve the data in forward direction and backsword direction

 What is set interface?   

Ø This can be used for representing a group of individual objects where duplicate objects are not allowed and insertion operation is not preserved.

Ø This is the child interface of collection

Ø  hashset and linkedHashSet are the classes which implements Set interface directly.

Ø It displays the data Random order

Ø Retrieve the data only in forward direction

What is Sorted Set interface?

Ø This can be used for representing a group of individual and unique objects. Where all the objects are inserted in some sorting order.

Ø  It is the child interface of Set interface

Ø TreeSet is the implemented class of SortedSet

Ø Retrieve the data only in forward direction and backward direction

What is  Queue interface?

Ø It is the child interface of collection it has introduced in 1.5 versions this interface can be used for representing a group of individual objects prior to processing.

Ø All the above interfaces(collection, List, Set, SortedSet, Queue) can be used for representing a group of individual objects.

Ø If u want to represent a group of objects as key value pair than we can’t use above interfaces.

Ø To handle this requirement sun people has introduced map interface.

What is Map Interface?

Ø This can be used for representing a group of objects as key value pairs. Both key and value are Objects only.

          Student Name     StudentRollNo

          PhoneNumber     contactdetails

          Word                    meaning                    

           IP Address          Domain-name

Ø Map interface is not child interface of collection

What is SortedMap interface?

Ø This can be used for representing a group of objects as key value pairs where all the entries are arranged in some sorting order of keys.

Ø TreeMap is the class which implements SortedMap interface.

Ø The following are legacy Characters in collection Frame Work.

          1) vector.-----------concrete class

          2) stack------------concrete class

          3) Hashtable-----concrete class

          4) properties------concreet class

          5) Dictionary--------abstract class

6) Enumeration-------interface

What is unidirectional and bidirectional objects?

Collection and Set organizes data only forward direction but not backward direction so these are called unidirectional objects

List and SortedSet organizes data both forward direction backward direction so these are called bidirectional objects

How do you add an element 60 at the end of List interface object?

List l=new List();

l.add(l.size(),newInteger(60));

          Collection Interface methods

This can be used for representing a group of individual objects as a single entity. This interface defines the

most common general methods. Which can be applicable for any collection implemented class

1)boolean add(Object obj)

This method is used to add any type of value(like int ,string….)  to the collection

2) boolean addAll(Collection c)

It is used to add the content of one collection variable to the another collection variable.It returns true doesn’t add the content of another variable.It returns false adds the content of one collection to another collection

3) boolean remove(Object obj)

4) boolean removeAll(Collection c)

(Removes particular group of objects.)

5) boolean retainAll(Collection c)

(Removes all the elements except those present in ‘c’)

6) void clear()

(Removies all objects.)

7) boolean contains(Object obj)

Checks object is there or not.It returns true the element is found in the collection.It returns false the element is not present in Collection

8) boolean contains (Collection c)

9) boolean isEmpty()

 

This is used to find a collection variable having entries or not.It returns true any  collection doesn’t have entries.It returns false any collection variable contains some entries

10) int size()

This is used to find the size of any collection

11) Object [] toArray()

 It is used to retrieve the data from the any collection framework variable in the form an array of objects of java.lang.Object

12) Iterator iterator()

This method is used to retrieve object one by one in any collection variable.It contains the next() and hasNext() methods

What is List interface?

This can be used for representing a group of individual objects where insertion order is preserved and duplicate objects are allowed. By means of index we can preserve insertion order and we can differentiate duplicate objects.

List Interface defines the following methods

1) Boolean add(Object obj)

Collection (1.2)

2) boolean add(int index, Object obj)

3) boolean addAll(Collection c)

4) boolean addAll(int index, Collection c)

5) boolean remove(Object obj)

6) Object remove(int index)

7) Object set(int index, Object new)

Old object. It replaces with the existing objected located at specified index with the new

object. And it returns object.

8) Object get(int index)

9) int indexOf(Object obj)

10) int lastIndexOf(Object obj)

11) ListIterator listIterator()

What is ArrayList?

Ø The underlying data Structure for ArrayList() is resizable Array or “Growable Array”.

Ø Duplicate objects are allowed.

Ø Insertion order is preserved.

Ø Heterogeneous objects are allowed.

Ø ‘null’ insertion is possible.

Constructors of Array List

ArrayList l = new ArrayList()

Creates an empty ArrayList object with default intitial capacity 10.

When ever ArrayList reaches its max capacity a new ArrayList Object will be created with new capacity.

Capacity=(current capacity*3/2)+1;

ArrayList l = new ArrayList(int initial capacity)

Creates an empty ArrayList Object with the specified initial capacity.

ArrayList l = new ArrayList(Collection c)

For inter conversion between collection objects.

What is the default initial capacity of ArrayList?

The default initial capacity of ArrayList is 10.

What are the common interfaces implemented by every collection?

Usually the collection objects can be used for data transport purpose and hence every collection implemented class already implemented serializable and cloneable interfaces.

What is the limitation ArrayList?

ArrayList is not recommended if the frequent operation is insertion or deletion in the middle.

To handle this requirement we should go for linked list.

What is LinkedList?

         

Ø The underlying Data Structure for linked list is doubly linked list.

Ø Duplicate objects are allowed.

Ø Insertion order is preserved.

Ø Heterogeneous objects are allowed.

Ø ‘null’ insertion is possible.

Ø Implements List, Queue, serializable, clonealbe Interfaces But not RandomAccess.

What is the use of LinkedList compared to ArrayList?

Ø LinkedList is the best choice if our frequent operation is insertion or deletion in the middle(no shift operations are required)

Ø LinkedList is the worst choice if our frequent operation is retrieval operation.

Ø LinkedList class usually used for implementing stacks and Queues to provide support for this requirement,

Ø LinkedList class contains the following specific methods.

     1. void addFirst(Object obj)

     2. void addLast(Object obj)

     3. Object removeFirst()

     4. Object removeLast()

     5. Object getFirst()

     6. Object getLast()

What are the constructers of LinkedList?

                   1. LinkedList l = new LinkedList()

              2. LinkedList l = new LinkedList(Collection c)

What is Vector class?

Ø The underlying Data structure for the vector is resizable array or growable array.

Ø Insertion order is preserved.

Ø Duplicate objects are allowed.

Ø ‘null’ insertion is possible.

Ø Heterogeneous objects are allowed.

Ø Best choice if the frequent operation is retrieval.

Worst choice if the frequent operation is insertion or deletion in the middle.

Vector class implemented serializable, cloneable and RandomAccess Interfaces

What is the Difference between vector and ArrayList?

Vector

1) All methods of vector are synchronized

2) vector object is thread safe

3) performance is low

4) 1.0 version(Legacy)

5.)Worst choice if the frequent operation is insertion or deletion in the middle.

 ArrayList

1) no method is synchronized

2) ArrayList object is not thread safe by default

3) performance is High

4) 1.2 version(non Legacy)

5.)ArrayList is the worst choice if u want to perform insertion or deletion in the middle.

What are the methods in Vector class?

For adding objects.

add(Object obj)

add(int index, Object obj)

addElement(Object obj)

For removing Objects

remove(Object obj)

removeElement (Object obj)

remove(int index)

removeElementAt(int index)

clear()

removeAllElements ()

For Accessing Elements

Object get(int index)

Object elementAt(int index)

Object firstElement();

Object lastElement();

Other Methods

int size();

int capacity();

enumeration elements();

constructors

Vector v = new Vector();

Creates an empty vector object with default initial capacity 10, when ever vector reaches it’s max capacity a new vector object will be created with.

New capacity=current capacity*2;

What is mean by stack?

It is the child class of Vector contains only one constructor.

Stack s = new Stack();

Methods

Object push(Object obj);

For inserting an object to the stack

Object pop();

It removes and returns top of the stack.

Object peak();

Returns the top of the stack with out removal of object.

int search(Object obj);

If the specified object is available it returns its offset from top of the stack

If the object is not available then it returns -1.

boolean empty();

returns true if the stack is empty otherwise false.

What are the cursors available in collection framework?

          Or

How are the retrieval objects in collection framework?

From the collection object to retrieve object we can use the following 3 cursors.

1. Enumeration

2. Interator

3. ListIterator

What is Enumaration (1.0)?

It is a predefined interface the functionality of this interface to retrieve the data from only in legacy collection classes in forward direction only

It is similar to iterator interface. It contains two methods

          1.Boolean hasMoreElements()

          2. Object NextElement ()  

Limitations of Enumeration

1. It is applicable only for legacy classes and it is not a universal cursor.

2. While iterating the elements by using enumeration we can perform only read operation and we can’t perform any modify/removal operations.

To overcome these problems we should go for Iterator   

What is an Iterator(1.2)?

It is a predefined interface the functionality of this interface also to restive the data from any collection framework variable only in forward direction

That’s why it called universal cursor. it contains three methods. to overcome the problems of Enumaration interface we can use Iterator interface

Limitations of Iterator

1. Enumeration and Iterator are single directional cursors. They can always move to words forward direction only.

2. By using Iterator we can perform read and remove operations. And we can’t perform any replace or addition of new objects

To over come these limitations we should go for list Iterator interface ().

What is ListIterator(1.2)?

It is predefined interface the functionality of this interface is also to retrieve the data from any collection both forward and backward directions

To overcome the problems of Enumaration and Iterator we can use ListIterator.By using this we can add, remove, replace and read the data.it contains nine methods

1. boolean hasNext();

2. boolean hasPrevious();

3. Object next();

4. Object previous();

5. int nextIndex();

If there is no next element it returns the size of the list

6. int previousIndex();

If there is no previous element it returns -1

7. void remove();

8. void set(Object new)

9. void set(Object new)

What is the difference b/w Enuaration and Iterator?

Iterator

1. Iterator object is not synchronized

2. Iterator is applicable for any collection (legacy and non legacy)

3. By sing this we can read and remove the objects

4. It is a universal cursor object

Enumaration

1. Enumaration object is synchronized

2. It is applicable for any non legacy collection classes

3. By sing this we can read the objects

4. It is not a universal cursor object

What are the legacy collection classes and interfaces present in collection framework?

The following are the legacy collection classes present in collection framework.

          1. Vector

          2. Stack

          3. HashTable

          4. Dictionary

          5. Properties

The following is the legacy collection interfaces present in collection framework.

          1. Enumaration

What is the diff b/w new and legacy collection framework?         

The major difference b/w these two is new collection framework classes and interfaces belongs to non-synchronized (provides concurrency) where as legacy collection framework classes and interfaces are synchronized(provides sequential)

What is Set Interface?

Ø This can be used for representing a group of Individual objects where insertion order is not preserved and duplicate objects are not allowed.

Ø Set interface is child interface of Collection.

Ø This interface doesn’t contain any new method and we have to use only collection Interface methods.

What is HashSet?

Ø The underlying Data Structure for HashSet is Hashtable.

Ø Insertion order is not preserved and it is based on has code of the Object.

Ø Duplicate objects are not allowed. Violation leads to no CompileTimeError or RuntimeError, add method simply returns false.

Ø ‘null’ insertion is possible.

Ø Heterogeneous objects are allowed.

Ø HashSet is the best choice if the frequent operation is Search Operation

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)

If we are trying to insert duplicate values in Set what will happen?

Ø Duplicate objects are not allowed. Violation leads to no CompileTimeError or RuntimeError, add method simply returns false.

What is LinkedHashSet?

It is the child class of HashSet. It is Exactly similar to HashSet. Except the following differences.

HashSet

1. Its equivalent data structure is HashTable

2. Displays the data in random order

3. Introduced in 1.2 version

LinkedHashSet

1. Its equivalent data structure is HashTable and  LinkedList

2. Displays the data in order

3. Introduced in 1.4 version

What is SortedSet?

Ø This can be used for representing a group of individual objects where duplicate objects are not allowed.

Ø Insertion order is not preserved but all the elements are inserted according to some sorting order of elements. The sorting order may be default natural sorting order or customized sorting order.

SortedSet Interface contains the following more specific methods

1.     Object first()

Returns first element in the SortedSet

2.     Object last()

3.     SortedSet headSet(Object obj)

Returns the SortedSet contains the elements which are less than object obj.

4.     SortedSet tailSet(Object obj)

Returns the SortedSet whose elements are greater than or equal to object obj

5.     SortedSet subSet(Object obj1, Object obj2)

Returns the SortedSet whose elements are >= obj1 but < Obj2

6.     Comparator comparator();

Returns the comparator object describes the underlying sorting technique.

If you are using default(Assending) natural sorting order it returns null.

Observe the following Example.

Ex:

100 120 130 140 150 160

first()  100

last()  160

headSet(140)  {100,120,130}

tailSet(140)  {140,150,160}

subset (130,150){130,140}

comparator ()  null

What is TreeSet?

Ø The underlying Data structure for the TreeSet is Balanced tree.

Ø Duplicate objects are not allowed. If we are trying to insert duplicate object we won’t get any compile time error or Run time error, add method simply returns false.

Ø Insertion order is not preserved but all the elements are inserted according to some sorting order.

Ø Heterogeneous objects are not allowed, violation leads to Run time error saying class cast Exception

Constructors

1. TreeSet t = new TreeSet();

Creates an empty TreeSet Object where the sorting order is default natural sorting

order.

2. TreeSet t= new TreeSet(Comparator c)

Creates an empty TreeSet Object where the Sorting order is specified by comparator object.

3. TreeSet t= new TreeSet(Collection c)

4. TreeSet t= new TreeSet(SortedSet s)

Creates TressSet Object for a given SortedSet.

What is Comparable Interface?

It is available in java.lang package. This interface contains only one method compareTo()

public int compareTo(Object obj)

obj1.compareTo(obj2)

Note: while Inserting the objects into the TreeSet JVM internally uses compareTo() method if we are depending on natural sorting order.

Sometimes we have to define our own customized sorting order, then we should go for comparator Interface.

What is Comparator?

It is an interface present in java.lang.util. the purpose of this is it will sort the objects ascending and descending order

.

By using comparator object we can define our own customized sorting.

 This interface defines the following 2 methods.

1) public int compare(Object obj1, Object obj2)

returns –ve if obj1 has to come before obj2

+ve if obj1 has to come after obj2

0 if obj1 and obj2 are equal.

2) public boolean equals(Object obj)

When ever we are implementing comparator interface compulsory we should provide implementation for compare method. Implementing equals method is optional because it is already available from object class through inheritance

What is Map interface?

The Map interface provides three collection views, which allow a map's contents to be viewed as a set of keys, collection of values, or set of key-value mappings.

 The order of a map is defined as the order in which the iterators on the map's collection views return their elements.

Map implemented by HashMap and TreeMap

What are the classes we have to implement the map interface?

A number of classes implement the Map interface, including HashMap, TreeMap, LinkedHashMap,WeakHashMap, ConcurrentHashMap, and Properties. The most generally useful class is HashMap.

Map interface methods

Here are some of the most useful Map methods.

Adding key-value pairs to a map

 Object obj = m.put(key, val) Creates mapping from key to val. It returns the previous value (or null)associated with the key.

m.putAll(map2) adds all key-value entries from another map, map2.

Removing key-value pairs from a map

m.clear() Removes all elements from a Map

 Object obj = m.remove(key) Deletes mapping from key to anything. Returns previous value (or null) associated with the key.

Retrieving information from the map

 Boolean b = m.containsKey(key) Returns true if m contains a key key

Boolean b = m.containsValue (Val) Returns true if m contains Val as one of the values

Object obj = m.get(key) Returns value corresponding to key, or null if there is no mapping. If null has been stored as a value, use containsKey to see if there is a mapping.

Boolean b = m.isEmpty() Returns true if m contains no mappings.

Integer i = m.size() Returns number of mappings in m.

Retrieving all keys, values, or key-value pairs (necessary for iteration)

Set set = m.entrySet () Returns set of Map.Entry values for all mappings.

Set set = m.keySet () Returns Set of keys.

col = m.values() Returns a Collection view of the values in m.

Map.Entry interface methods

Each element is a map has a key and value. Each key-value pair is saved in a java.util.Map.Entry object.

A set of these map entries can be obtained by calling a map's entrySet() method. Iterating over a map is done by iterating over this set.

Assume in the following table that me is a Map. Entry object.

Object obj = me.getKey() Returns the key from the pair.

Object obj = me.getValue (key) Returns the value from the Map pair.

Object obj = me.setValue (val) This is an optional operation and may not be supported by all Map.Entry objects. Sets the value of the pair, which modifies the Map which it belongs to. Returns the orginal value.

The interface methods can be broken down into three sets of operations: altering, querying and providing Alternative views

The alteration operation allows you to add and remove key-value pairs from the map. Both the key and Value can be null. However you should not add a Map to itself as a key or value.

Object put (Object key, Object value)

Object remove(Object key)

void putAll(Map t)

void clear()

The query operations allow you to check on the contents of the map

Object get(Object key)

boolean containsKey(Object key)

boolean containsValue(Object value)

int size()

Boolean isEmpty()    

The set methods allow you to work with the group of keys or values as a collection

Set keySet()

Collection values()

Set entrySet()

What is HashMap?

HashMap is not sorted or ordered. If you just need a Map, and you don’t care about the order of the elements while iterating through it, you can use a HashMap. That keeps it simple.

The values can be null. But the key should ne unique, so you can have one null value for key. (Allows only one null key).

HashMap class constructors

In addition to implemented the Map interface methods, HashMap has the following constructors.

HashMap map= new HashMap ()

 Creates a new HashMap with default initial capacity 16 and load factor 0.75.

HashMap map= new HashMap (initialCapacity)

Creates a new HashMap with the specified initial int capacity.

HashMap map  = new HashMap(initialCapacity,loadFactor)

Creates a new HashMap with the specified capacity which will not exceed a specified (float) load factor.

HashMap map = new HashMap(mp)

 Creates a new HashMap with elements from the Map mp

HashMap is implemented with a hash table. Access time is O(1). Entries are unsorted

What is LinkedHashMap?

LinkedHashMap will keep the order in which the elements are inserted into it. If you will be adding and removing elements a lot, it will be better to use HashMap, because LinkedHashMap will be slower to dothose operations. But, you can iterate faster using LinkedHashMap. So, if you will be iterating heavily, it may be a good idea to use this.

What is WeakHashMap?

A map of weak keys that allow objects referred to by the map to be released; designed to solve certain types of problems. If no references outside the map are held to a particular key, it may be garbage collected.

What is IdentityHashMap?

A hash map that uses == instead of equals ( ) to compare keys. Only for solving special types of problems not for general use.

What is Hashtable?

Hashtable is almost the same as HashMap. The main differences are:

1. Hashtable does not let you have null value for key.

2. The key methods of Hashtable are synchronized. So, they may take a longer time to execute, compared to HashMap’s methods.

What is SortedMap?

If you have a SortedMap (of which TreeMap is the only one available), the keys are guaranteed to be in sorted order, which allows additional functionality to be provided with these methods in the SortedMap interface: 

Comparator comparator( ): Produces the comparator used for this Map, or null for natural ordering.

Object firstKey( ): Produces the lowest key.

Object lastKey( ): Produces the highest key.

SortedMap subMap(fromKey, toKey): Produces a view of this Map with keys from fromKey, inclusive,to toKey, exclusive.

SortedMap headMap (toKey): Produces a view of this Map with keys less than toKey.SortedMap tailMap(fromKey): Produces a view of this Map with keys greater than or equal to fromKey.

SortedMap interface methods

The SortedMap interface is used by TreeMap and adds additional methods to reflect that a TreeMap is sorted.

comp = comparator() Returns Comparator used to compare keys. null if natural ordering used(eg, String).

obj = firstKey() Key of first (in sorted order) element.

obj = lastKey() Key of last (in sorted order) element.

smp = headMap(obj) Returns SortedMap of all elements less than obj.

smp = tailMap(obj) Returns SortedMap of all elements greater than or equal to obj.

smp = subMap(fromKey,toKey)

Returns SortedMap of all elements greater than or equal to fromKey and

less than toKey.

What is TreeMap?

TreeMap is a sorted Map and will be sorted by the natural order of the elements. If you want, you can define a custom sort order by means of a Comparator passed to the constructor. So, when you need a custom sort order, it is clear which class you should be using!

TreeMap class constructors

TreeMap implements the Map and SortedMap interface methods. In constrast to HashMap, TreeMap keeps the balanced binary tree in sorted order by key.

 If the key has a natural order (eg, String) this is ok, but often you will supply a Comparator object that tells how two keys compare. It has the following constructors.

SortedMap tmap = new TreeMap()

Creates new TreeMap. Keys sorted by natural order.

SortedMap tmap = new TreeMap (comp)

 Creates new TreeMap using Comparator comp to sort keys.

SortedMap tmap = new TreeMap (mp)

new TreeMap from Map mp using natural ordering.

SortedMap tmap = new TreeMap(smp)

Creates new TreeMap from SortedMap smp using key ordering from smp.

j

 .TreeMap is implemented as a balanced binary tree. Access time is O(log N). Entries are

sorted.

           

What is the internal concept of ArrayList?

                             Arrays, type single dimensional

What is the internal design of HashMap?

                                      Arrays

what is the internal design of Hash Set

HashMap