1. COP 3503 FALL 2012 Shayan Javed Lecture 8
Programming Fundamentals using Java

2. ArrayList and Java Generics

3. Collection
A container object that groups multiple objects

4. Collection A container object that groups multiple objects
Example: Arrays

5. Collection A container object that groups multiple objects
Example: Arrays
Java provides multiple classes/interfaces in the Java Collection Framework

6. Collection A container object that groups multiple objects
Example: Arrays
Java provides multiple classes/interfaces in the Java Collection Framework
Going to look at ArrayList

7. Arrays
Hold several elements (primitives/objects) of the same type

8. Arrays Hold several elements (primitives/objects) of the same type
Size = static.
Once set, cannot be changed

9. Arrays
Advantages:
Easy to access elements directly

10. Arrays
Advantages:
Easy to access elements directly
Easy to traverse

11. Arrays Advantages: Disadvantages: Easy to access elements directly
Easy to traverse
Disadvantages:
Have to decide on size before creating

12. Arrays Advantages: Disadvantages: Easy to access elements directly
Easy to traverse
Disadvantages:
Have to decide on size before creating
Inserting/removing elements is troublesome
Shifting elements

13. ArrayList (java.util.ArrayList)
Holds several objects in order (like Arrays)

14. ArrayList (java.util.ArrayList)
Holds several objects in order (like Arrays)
Unlike Arrays:
Size does not need to be specified at creation time

15. ArrayList (java.util.ArrayList)
Holds several objects in order (like Arrays)
Unlike Arrays:
Size does not need to be specified at creation time
Grows in size as items added

16. ArrayList (java.util.ArrayList)
Holds several objects in order (like Arrays)
Unlike Arrays:
Size does not need to be specified at creation time
Grows in size as items added
Provides useful methods for manipulating the list

17. ArrayList (java.util.ArrayList)
Constructors:
new ArrayList( ) - no need to pass in size (10)

18. ArrayList (java.util.ArrayList)
Constructors:
new ArrayList( ) - no need to pass in size (10)
new ArrayList(int) - initial capacity

19. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list

20. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index

21. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements

22. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list

23. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index

24. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list

25. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list
Object remove(int index): Removes the object at the index

26. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list
Object remove(int index): Removes the object at the index
int size(): Returns the no. of elements in the list

27. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list
Object remove(int index): Removes the object at the index
int size(): Returns the no. of elements in the list
int indexOf(Object o): Returns index of first matching element

28. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list
Object remove(int index): Removes the object at the index
int size(): Returns the no. of elements in the list
int indexOf(Object o): Returns index of first matching element
Object set(int index, Object o): Sets the object at the index

29. ArrayList (java.util.ArrayList)
Methods:
boolean add(Object o): Appends object at the end of the list
void add(int index, Object o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(Object o): Returns true if object is in the list
Object get(int index): Returns object at the index
boolean remove(Object o): Removes the object from the list
Object remove(int index): Removes the object at the index
int size(): Returns the no. of elements in the list
int indexOf(Object o): Returns index of first matching element
Object set(int index, Object o): Sets the object at the index
Object clone(): Returns a shallow copy

30. ArrayList Example
import java.util.ArrayList;

31. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially

32. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10));

33. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */

34. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ int sum = 0; // sum up all the numbers in the list int number = 0;

35. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { }

36. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = (Integer)numbers.get(i); // cast required – why? }

37. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = (Integer)numbers.get(i); // cast required – why? sum += number; // auto un-boxing: Integer converted to int }

38. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ numbers.add(“A String”); // will compile! int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = (Integer)numbers.get(i); // cast required – why? sum += number; // auto un-boxing: Integer converted to int }

39. ArrayList Example
import java.util.ArrayList; ArrayList numbers = new ArrayList(); // no size specified initially numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: converted to numbers.add(new Integer(3)); */ numbers.add(“A String”); // will compile! int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = (Integer)numbers.get(i); // run-time error when i = 2 sum += number; // auto un-boxing: Integer converted to int }

40. How do we make sure we are dealing with objects of only one type?
ArrayList
How do we make sure we are dealing with objects of only one type?

41. ArrayList
How do we make sure we are dealing with objects of only one type? Solution: Java Generics

42. Java Generics
Generics is the capability to parameterize types

43. Java Generics Generics is the capability to parameterize types
Can define class/interface/method with generic types – compiler replaces with concrete types.

44. Java Generics Generics is the capability to parameterize types
Can define class/interface/method with generic types – compiler replaces with concrete types.
Introduced in JDK 1.5

45. java.util.ArrayList<E>
Methods:
boolean add(E o): Appends object at the end of the list
void add(int index, E o): Inserts object at specified index
void clear(): Removes all elements
boolean contains(E o): Returns true if object is in the list
E get(int index): Returns object at the index
boolean remove(E o): Removes the object from the list
E remove(int index): Removes the object at the index
int size(): Returns the no. of elements in the list
int indexOf(E o): Returns index of first matching element
E set(int index, E o): Sets the object at the index
E clone(): Returns a shallow copy

46. Java Generics
Type of objects it can hold is specified at declaration

47. Java Generics Type of objects it can hold is specified at declaration
// will only hold Integer objects
ArrayList<Integer> numbers = new ArrayList<Integer>();

48. ArrayList Example
import java.util.ArrayList; ArrayList<Integer> numbers = new ArrayList<Integer>(); numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: */ numbers.add(“A String”); // WON’T COMPILE! int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = (Integer)numbers.get(i); // cast NOT required – why? sum += number; // auto un-boxing: Integer converted to int }

49. ArrayList Example
import java.util.ArrayList; ArrayList<Integer> numbers = new ArrayList<Integer>(); numbers.add(new Integer(10)); numbers.add(3); /* auto-boxing: */ numbers.add(“A String”); // WON’T COMPILE! int sum = 0; // sum up all the numbers in the list int number = 0; for(int i = 0; i < numbers.size(); i++) { number = numbers.get(i); // cast NOT required – why? sum += number; // auto un-boxing: Integer converted to int }

50. Java Generics
More strictness

51. Java Generics
More strictness
Fewer errors

52. Generic Classes
public class AClass<E> { // properties and methods can use the “E” type }

53. Generic Classes
public class AClass<E> { // properties and methods can use the “E” type ArrayList<E> numbers = new ArrayList<E>(); }

54. Generic Methods
public class GenericMethodDemo { public static void main(String[] args ) { Integer[] integers = {1, 2, 3, 4, 5}; String[] strings = {"London", "Paris", "New York”}; }

55. Generic Methods
public class GenericMethodDemo { public static void main(String[] args ) { Integer[] integers = {1, 2, 3, 4, 5}; String[] strings = {"London", "Paris", "New York”}; } public static <E> void print(E[] list) { for (int i = 0; i < list.length; i++) System.out.print(list[i] + " "); System.out.println(); }

56. Generic Methods
public class GenericMethodDemo { public static void main(String[] args ) { Integer[] integers = {1, 2, 3, 4, 5}; String[] strings = {"London", "Paris", "New York”}; GenericMethodDemo.<Integer>print(integers); GenericMethodDemo.<String>print(strings); } public static <E> void print(E[] list) { for (int i = 0; i < list.length; i++) System.out.print(list[i] + " "); System.out.println(); }

57. Generic Interfaces
public interface AnInterface<E> { // properties and methods can use the “E” type public void aMethod(E object); }

58. Generic Interfaces
public interface Comparable<E> { public int compareTo(E object); }

59. Generic Interfaces
public interface Comparable<E> { public int compareTo(E object); } public interface Comparator<E> { public int compare(E object1, E object2);

60. Generic Interfaces
public Book implements Comparable{ // comparison based on price public int compareTo(Object o) { Book b = (Book)o; if (price > b.getPrice()) return 1; else if (price < b.getPrice()) return -1; else return 0; }

61. Generic Interfaces
public Book implements Comparable{ // comparison based on price public int compareTo(Object o) { Book b = (Book)o; if (price > b.getPrice()) return 1; else if (price < b.getPrice()) return -1; else return 0; } } HOW WOULD YOU USE JAVA GENERICS?

62. Generic Interfaces
public Book implements Comparable<Book>{ // comparison based on price public int compareTo(Book b) { Book b = (Book)o; if (price > b.getPrice()) return 1; else if (price < b.getPrice()) return -1; else return 0; }

63. Generic Interfaces
public Book implements Comparable<Book>{ // comparison based on price public int compareTo(Book b) { Book b = (Book)o; // no more casting! if (price > b.getPrice()) return 1; else if (price < b.getPrice()) return -1; else return 0; }

64. Generic Interfaces
public Book implements Comparable<Book>{ // comparison based on price public int compareTo(Book b) { Book b = (Book)o; // no more casting! if (price > b.getPrice()) return 1; else if (price < b.getPrice()) return -1; else return 0; }

65. Generic Interfaces
public class ReviewComparison implements Comparator { public int compare (Object o1, Object o2) { Book b1 = (Book)o1; Book b2 = (Book)o2; if (b1.getACR() > b2.getACR()) return 1; if (b1.getACR() < b2.getACR()) return -1; else return 0; }

66. Generic Interfaces
public class ReviewComparison implements Comparator<Book> { public int compare (Book b1, Book b2) { Book b1 = (Book)o1; Book b2 = (Book)o2; if (b1.getACR() > b2.getACR()) return 1; if (b1.getACR() < b2.getACR()) return -1; else return 0; }

67. Generic Interfaces
public class ReviewComparison implements Comparator<Book> { public int compare (Book b1, Book b2) { Book b1 = (Book)o1; Book b2 = (Book)o2; if (b1.getACR() > b2.getACR()) return 1; if (b1.getACR() < b2.getACR()) return -1; else return 0; }

68. Java Generics - Summary
Allows you to create a “general” template
Classes/methods/interfaces
Versatile and strict

69. Back to ArrayList...
How does it work “behind the scenes”?

70. Back to ArrayList... How does it work “behind the scenes”?
Elements are stored inside an array
private array

71. Back to ArrayList... How does it work “behind the scenes”?
Elements are stored inside an array
private array
Array has an initial capacity

72. Back to ArrayList... How does it work “behind the scenes”?
Elements are stored inside an array
private array
Array has an initial capacity
Empty constructor [new ArrayList()]: capacity 10

73. Back to ArrayList... How does it work “behind the scenes”?
Elements are stored inside an array
private array
Array has an initial capacity
Empty constructor [new ArrayList()]: capacity 10
Otherwise specify capacity [new ArrayList(capacity)]

74. ArrayList
When number of elements exceeds capacity (the add/insert method):

75. ArrayList
When number of elements exceeds capacity (the add/insert method):
Internal array replaced by new one

76. ArrayList
When number of elements exceeds capacity (the add/insert method):
Internal array replaced by new one
Elements from the old array copied over

77. ArrayList
When number of elements exceeds capacity (the add/insert method):
Internal array replaced by new one
Elements from the old array copied over
Insert and remove require shifting of elements

78. ArrayList
When number of elements exceeds capacity (the add/insert method):
Internal array replaced by new one
Elements from the old array copied over
Insert and remove require shifting of elements
(Recall add/remove in Project1)

79. Efficiency of ArrayLists
Reallocation of underlying array = when capacity reached and need to add more elements

80. Efficiency of ArrayLists
Reallocation of underlying array = when capacity reached and need to add more elements
Add/Insert/Remove = costly because requires shifting of elements in array

81. Efficiency of ArrayLists
Reallocation of underlying array = when capacity reached and need to add more elements
Add/Insert/Remove = costly because requires shifting of elements in array
Accessing element (get) = fast just like an array

82. Efficiency of ArrayLists
Reallocation of underlying array = when capacity reached and need to add more elements
Add/Insert/Remove = costly because requires shifting of elements in array
Accessing element (get) = fast just like an array
Problems overcome with Linked Lists.

83. Other Java Collections
LinkedList
Stack
Queue
Will look at these later