The document discusses Java collections and the collection framework. It provides an overview of different collection interfaces like List, Set, Queue and their implementations like ArrayList, LinkedList, Stack. It describes how the collection framework was designed to be high-performance and allow different collection types to work similarly. It also discusses accessing elements in a collection using iterators.

1. Collections

2. Collection
 Prior to Java 2, Java provided ad hoc classes such
as Dictionary, Vector, Stack, and Properties to
store and manipulate groups of objects.
 Although these classes were quite useful, they
lacked a central, unifying theme.
 Thus, the way that you used Vector was different
from the way that you used Properties.
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3. Collection Framework
 The Collection in Java is a framework that
provides an architecture to store and manipulate
the group of objects.
 Java Collections can achieve all the operations
that you perform on a data such as searching,
sorting, insertion, manipulation, and deletion.
 Java Collection means a single unit of objects.
Java Collection framework provides many
interfaces (Set, List, Queue, Deque) and classes
(ArrayList, Vector, LinkedList, PriorityQueue,
HashSet, LinkedHashSet, TreeSet).
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4. Collection Framework
 The collections framework was designed to meet
several goals, such as −
The framework had to be high-performance.
The implementations for the fundamental
collections (dynamic arrays, linked lists, trees,
and hashtables) were to be highly efficient.
The framework had to allow different types of
collections to work in a similar manner and with
a high degree of interoperability.
The framework had to extend and/or adapt a
collection easily.
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5. What is a framework in Java?
 It provides readymade architecture.
 It represents a set of classes and interfaces.
 It is optional.
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6. Collection Hierarchy
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7. Collection Hierarchy
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 A collections framework is a unified architecture
for representing and manipulating collections. All
collections frameworks contain the following −
Interfaces
Implementations, i.e., Classes
Algorithms

8. Interfaces
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 Iterable
 Collection
 List
 Queue
 Deque
 Set

9. List Interface
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 The List interface extends Collection and declares
the behavior of a collection that stores a sequence of
elements.
 Elements can be inserted or accessed by their position in the
list, using a zero-based index.
 A list may contain duplicate elements.
 In addition to the methods defined by Collection, List
defines some of its own, which are summarized in the
following table.
 Several of the list methods will throw an
UnsupportedOperationException if the collection cannot be
modified, and a ClassCastException is generated when one
object is incompatible with another.

10. List Interface Implementations
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 Stack
 LinkedList
 ArrayList

11. Stack
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 Stack is a subclass of Vector that implements a
standard last-in, first-out stack.
 Both Stack and Vector classes are available from
Java 1.0.
 These two classes are called Legacy Classes.
 Both are ThreadSafe with Synchronized Methods.
 Stack only defines the default constructor, which
creates an empty stack. Stack includes all the
methods defined by Vector, and adds several of
its own.
Stack()

12. Methods in Stack
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Method Description
boolean empty() Tests if this stack is empty. Returns true
if the stack is empty, and returns false if
the stack contains elements.
Object peek( ) Returns the element on the top of the
stack, but does not remove it.
Object pop( ) Returns the element on the top of the
stack, removing it in the process.
Object push(Object element) Pushes the element onto the stack.
Element is also returned.
int search(Object element) Searches for element in the stack. If
found, its offset from the top of the
stack is returned. Otherwise, -1 is
returned.

13. Example
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StackDemo.java

14. LinkedList
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 Java LinkedList class uses a doubly linked list to
store the elements. It provides a linked-list data
structure. It inherits the AbstractList class and
implements List and Deque interfaces.
 The important points about Java LinkedList are:
 Java LinkedList class can contain duplicate elements.
 Java LinkedList class maintains insertion order.
 Java LinkedList class is non synchronized.
 In Java LinkedList class, manipulation is fast because no
shifting needs to occur.
 Java LinkedList class can be used as a list, stack or
queue.

15. LinkedList
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 Java LinkedList class uses a doubly linked list to
store the elements. It provides a linked-list data
structure. It inherits the AbstractList class and
implements List and Deque interfaces.
 The important points about Java LinkedList are:
 Java LinkedList class can contain duplicate elements.
 Java LinkedList class maintains insertion order.
 Java LinkedList class is non synchronized.
 In Java LinkedList class, manipulation is fast because no
shifting needs to occur.
 Java LinkedList class can be used as a list, stack or
queue.

16. Methods of LinkedList
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Method Description
boolean add(E e)
It is used to append the specified
element to the end of a list.
void add(int index, E element)
It is used to insert the specified
element at the specified position
index in a list.
void addFirst(E e)
It is used to insert the given
element at the beginning of a list.
void addLast(E e)
It is used to append the given
element to the end of a list.
boolean contains(Object o)
It is used to return true if a list
contains a specified element.
E element()
It is used to retrieve the first
element of a list.
E get(int index)
It is used to return the element
at the specified position in a list.

17. Methods of LinkedList
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Method Description
E get(int index)
It is used to return the element at the specified
position in a list
E getFirst() It is used to return the first element in a list.
E getLast() It is used to return the last element in a list.
int indexOf(Object o)
It is used to return the index in a list of the first
occurrence of the specified element, or -1 if the
list does not contain any element.
int lastIndexOf(Object o)
It is used to return the index in a list of the last
occurrence of the specified element, or -1 if the
list does not contain any element.
E peek() It retrieves the first element of a list
E remove()
It is used to retrieve and removes the first
element of a list.
E removeFirst()
It removes and returns the first element from a
list.

18. Example
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LLDemo.java

19. Arrays
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 The java.util.Arrays class contains a static
factory that allows arrays to be viewed as lists.
 Following are the important points about Arrays −
This class contains various methods for
manipulating arrays (such as sorting and
searching).
The methods in this class throw a
NullPointerException if the specified array
reference is null.

20. Example
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ArraysDemo.java

21. ArrayList
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 Java ArrayList class uses a dynamic array for storing
the elements. It inherits AbstractList class and
implements List interface.
 The important points about Java ArrayList class are:
 Java ArrayList class can contain duplicate elements.
 Java ArrayList class maintains insertion order.
 Java ArrayList class is non synchronized.
 Java ArrayList allows random access because array works at
the index basis.
 In Java ArrayList class, manipulation is slow because a lot of
shifting needs to occur if any element is removed from the
array list.

22. ArrayList
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 The ArrayList contains the following Constructors
to initialize.
ArrayList()
ArrayList(int capacity)

23. Example
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ALDemo.java

24. Accessing a Collection
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 To access any Collection, We can use the Iterator
interface.
 An iterator is an interface that is used in place of
Enumerations in the Java Collection Framework.
Moreover, an iterator differs from the
enumerations in two ways:
 Iterator permits the caller to remove the given
elements from the specified collection during the
iteration of the elements.
 Method names have been enhanced.
 Iterator interface is a member connected with
Java Collections Framework.

25. Methods of Iterator
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Methods Description
forEachRemaining(Consumer<? super
E>action)
Performs the given action on each of
the element until and unless all the
elements have been processed or
unless an exception is thrown by the
action.
hasNext()
Returns a true value if the more
number of elements are encountered
during iteration.
next()
Returns the next specified element
during the iteration.
remove()
Removes the last element from the
collection as provided by the iterator.