1 Copyright © 2011 Tata Consultancy Services Limited COLLECTIONS By TEAM 5 Rajendhiran Sivan Christi Yashwanth Bijay Smruthi Satyajit

2 Introduction to Collections  Collections in java is a framework that provides an architecture to store and manipulate the group of objects.  Data Operations like:  Searching  Sorting  Insertion  Manipulation  Deletion

3 Hierarchy of Collection Framework

4 Benefits of the Java Collections Framework  Reduces programming effort.  Increases program speed and quality.  Fosters software reuse.

5 Some Functions Related To Map CLEAR- Removes all elements from map GET- Retrieve values of Requested key KEYSET- Returns set that contains all keys REMOVE- Removes requested Key and it’ values from Map SIZE- Returns number of key value pairs in the map EQUALS- Compares an object with Map for Equality

6 Iterator Interface  To retrieve the elements one by one from a collection object.  Three methods: -boolean hasNext () -element next () -void· remove ()

7 ListIteartor Interface  To retrieve the elements from a collection object, both in forward and reverse directions.  Important methods: -boolean hasNext () -boolean has Previous () -element next () -element previous () -void remove ()

8 Difference between Iterator and ListIterator IteratorListIterator Only forward directionForward and Backward direction Less preferredMore preferred

9 Example ArrayList al = new ArrayList(); // use iterator to display contents of al system.out.print("original contents of al: "); Iterator itr = al.Iterator(); while(itr.hasnext()) { object element = itr.next(); system.out.print(element + " "); } // Modify objects being iterated ListIterator litr = al.listIterator(); while(litr.hasNext()) { Object element = litr.next(); litr.set(element + "+"); } System.out.print("Modified contents of al: "); itr = al.iterator(); while(itr.hasNext()) { Object element = itr.next(); System.out.print(element + " "); } System.out.println();

10 List Interface  Ordering  Duplicate  Operation  Manages its own Size

11 Java's List interface Java also has an interface java.util.List to represent a list of objects. It adds the following methods to those in Collection : (a partial list) Some are: public void add(int index, Object o) public Object get(int index) public Object remove(int index) public Object set(int index, Object o)

12  ArrayList  LinkedList Array

13 Set Interface  Set is an group element arranged like an Array.  Grow dynamically.  Not allow duplicate elements.

14 Difference Bitween Set and Maps SetList Doesn’t allow duplicatesAllow duplicates Unordered collectionOrdered collection

15 Set Methods  add()  clear()  contains()  size()  isEmpty()  iterator()  Remove()

16 Various Implementaion of Set Interface  HashSet  TreeSet  LinkedHashSet

17 HashSet  Set of elements(objects).  Uses HashTable to store the elements.  Extends abstract class and implements Set interface.  Contains unique elements only.

18 HashSet Example HashSet al=new HashSet (); al.add("Ravi"); al.add("Vijay"); Iterator itr=al.iterator(); while(itr.hasNext()) { System.out.println(itr.next()); }

19 HashSet  Syntax: - HashSet al=new HashSet ();  Create hashset object:- -HashSet assetSet=new HashSet(); // HashSet insance without any element -HashSet from ArrayList=new HashSet(Arrayas.asList("Java","c++); //copying content -HashSet properSet=new HashSet(50); //HashSet with initial capacity

20 TreeSet  Contains unique elements.  Implements NavigableSet interface.  Extends SortedSet interface.  Maintains ascending order.

21 TreeSet  Syntax: -TreeSet al=new TreeSet ();  Example: TreeSet al=new TreeSet (); al.add("Ravi"); al.add("Vijay"); Iterator itr=al.iterator(); while(itr.hasNext()) { System.out.println(itr.next()); }

22 LinkedHashSet  Subclass of HashSet.  Generic class.  Declaration: -class LinkedHashSet  Internally uses a linked list to store the element.

23 Map Defination and Types  MAP is an object that maps keys to values.  Restrictions: -No duplicate keys are allowed in map. -Each key can map to at most one value.  TYPES- 1.HashMap 2.TreeMap 3.Linked HashMap

24 TreeSet  Syntax: -TreeSet al=new TreeSet ();  Example: TreeSet al=new TreeSet (); al.add("Ravi"); al.add("Vijay"); Iterator itr=al.iterator(); while(itr.hasNext()) { System.out.println(itr.next()); }

25 Diferences Bitween Different Maps  HashMap has no guarantee about it’s Iteration Order.  TreeMap Iterates according to their natural ordering of the keys.  Linked HashMap Iterates according to the order in which the entries were put into the map.

26 TreeSet  Syntax: - TreeSet al=new TreeSet ();  Example: TreeSet al=new TreeSet (); al.add("Ravi"); al.add("Vijay"); Iterator itr=al.iterator(); while(itr.hasNext()) { System.out.println(itr.next()); }

27 How to use Map in Java

28 Some Functions Related To Map CLEAR- Removes all elements from map GET- Retrieve values of Requested key KEYSET- Returns set that contains all keys REMOVE- Removes requested Key and it’ values from Map SIZE- Returns number of key value pairs in the map EQUALS- Compares an object with Map for Equality

29 Comparable Interface  To order the objects.  java.lang package.  compareTo(Object).  Single sorting sequence.

30 Comparable Interface  public int compareTo(Object obj)  public void sort(List list)

31 Comparable Interface class Student implements Comparable{ int rollno; String name; int age; Student(int rollno,String name,int age) { this.rollno=rollno; this.name=name; this.age=age; } public int compareTo(Object obj){ Student st=(Student)obj; if(age==st.age) return 0; else if(age>st.age) return 1; else return -1; } S Student.java AgeComparator.java Collections.sort(al);

32 Comparator Interface  To order the objects.  compare(Object obj1,Object obj2).  equals(Object element).  Multiple sorting sequence.

33 Comparator Interface  public int compare(Object obj1,Object obj2)  public void sort(List list,Comparator c)

34 Comparator Interface SStudent.javaAgeComparator.jav a class AgeComparator implements Comparator{ public int Compare(Object o1,Object o2){ Student s1=(Student)o1; Student s2=(Student)o2; if(s1.age==s2.age) return 0; else if(s1.age>s2.age) return 1; else return -1; a } Collections.sort(al,new AgeComparator()); Collections.sort(al,new NameComparator()); class Student{ int rollno; String name; int age; Student(int rollno,String name,int age) { this.rollno=rollno; this.name=name; this.age=age; }

35 Difference between Comparable and Comparator ComparableComparator Single sorting sequenceMultiple sorting sequence Affects the original classDoesn't affect the original class compareTo()compare() java.langjava.util Collections.sort(List)Collections.sort(List,Comparator)

36 Introduced in J2SE-5 Deals with type-safe objects Syntax : ClassOrInterface Eg. ArrayList JAVA GENERICS

37 ADVATAGES OF JAVA GENERICS 1. Type -safety 2. Type -casting Not Required 3. Compile time checking

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