The document discusses Java collection framework. It defines a collection as an object that groups multiple elements into a single unit. The main collections covered are ArrayList, LinkedList, HashSet, TreeSet, and HashMap. ArrayList uses a dynamic array and allows duplicates. LinkedList uses doubly linked lists and maintains insertion order but has no random access. HashSet and TreeSet contain unique elements only, with TreeSet maintaining ascending sort order. HashMap maps keys to values and may have one null key but multiple null values, with no defined ordering. Commonly thrown exceptions for collections include IndexOutOfBounds, ClassCast, NullPointer, IllegalArgument and IllegalState exceptions. Iterators and for-each loops can be used to traverse collection

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Collection Framework

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Reduces programming effort
>Increases program speed and quality
>Reduce effort to learn and use new APIs
 Is simply an object that groups multiple elements
into a single unit.
 Sometimes called a container
 Collections are used to store, retrieve, manipulate,
and communicate aggregate data
Benefits of Collection Framework
What is a Collection?

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The Collections Hierarchy

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Collection Framework
 ArrayList Class
 LinkedList Class
 HashSet Class
 LinkedHaseSet Class
 TreeSet Class
 Map Interface
 LinkedHashMap Class
 TreeMap Class
 Hashtable Class
 Comparable Interface
 Comparator Interface
 HashMap Class

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Commonly thrown Exceptions in Collection Framework
 UnSupportedOperationException
 occurs if a Collection cannot be modified.
 ClassCastException
 occurs when one object is incompatible with another.
 NullPointerException
 occurs when you try to store null object in Collection.
 IllegalArgumentException
 thrown if an invalid argument is used.
 IllegalStateException
 thrown if you try to add an element to an already full Collection.

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Hierarchy of ArrayList class:
ArrayList<Integer> list = new ArrayList<Integer>(0);
list.add(1001);
list.add(1002);
System.out.println(list.get(5));
Exception:
java.lang.IndexOutOfBoundsException:
Index: 4, Size: 2
IndexOutOfBoundsException

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ArrayList class:
 Uses a dynamic array for storing the elements.It extends
AbstractList class and implements List interface.
 Can contain duplicate elements.
 It Maintains insertion order.
 Not synchronized.
 Random access because array works at the index basis.
 Manipulation slow because a lot of shifting needs to be
occurred.

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Methods of Collection interface
public boolean equals(Object element) : matches two collection.

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Example of addAll(Collection) method:

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Example of removeAll() method:

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Example of retainAll() method:

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By Iterator interface.
package Collection;
import java.util.ArrayList;
import java.util.Iterator;
public class Array1 {
public static void main(String[] args) {
ArrayList alist=new ArrayList();
alist.add("Ravi");
alist.add("Vijay");
alist.add("Ravi");
Iterator itr=alist.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
} }}
Output:
Ravi
Vijay
Ravi

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ArrayList: By for-each loop.

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LinkedList class:
 Uses doubly linked list to store the elements. It extends the
AbstractList class and implements List and Deque
interfaces.
 Can contain duplicate elements.
 Maintains insertion order.
 Not synchronized.
 No random access.
 Manipulation fast because no shifting needs to be occurred.

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Difference between List and Set:
List can contain duplicate elements
whereas
Set contains unique elements only.

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Linked List

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HashSet class:
 Uses hashtable to store the elements.It extends
AbstractSet class and implements Set interface.
 contains unique elements only.
HashSet hs=new HashSet();
hs.add("Ravi");
hs.add("Vijay");
Iterator itr=hs.iterator();
while(itr.hasNext()){
System.out.println(itr.next());
Output:
Ravi
Vijay

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TreeSet class:
1. Contains unique elements
only like HashSet.
2. The TreeSet class
implements NavigableSet
interface that extends the
SortedSet interface.
3. Maintains ascending order.

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Treeset
Output:
Ravi
vijay

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HashMap
 A HashMap contains values based on the key. It implements
the Map interface and extends AbstractMap class.
 It contains only unique elements.
 It may have one null key and multiple null values.
 It maintains no order.

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HashMap class:
Hierarchy of HashMap
 What is difference
between HashSet and
HashMap?
HashSet contains only
values whereas HashMap
contains entry(key and
value).

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HashMap

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