1. Java Programming: Guided Learning with Early Objects
Chapter 12
Generics, Dynamic Representations, and Collections

2. Objectives Learn about generic methods and classes
Learn about the interface Comparable and how to implement it
Learn about the Java class LinkedList and how to use various operations of this class
Java Programming: Guided Learning with Early Objects

3. Objectives (continued)
Explore iterators and how they work
Learn about the interface Collection and its framework
Learn about various collection algorithms
Java Programming: Guided Learning with Early Objects

4. Generic Methods
Generic methods: write one method definition rather than multiple definitions
Defined using type parameters
Type parameter section precedes return type of the method
Type parameters separated by commas
Enclosed in angle brackets
Also called type variables
Java Programming: Guided Learning with Early Objects

5. Generic Methods (continued)
Type parameters used for:
Declaring return type of the method
Declaring formal parameters
Declaring local variables
Type parameters represent only reference parameters
Not primitives
modifiers <T> returnType methodName (formal parameter list) {
// Method body }
Java Programming: Guided Learning with Early Objects

6. Generic Classes Type parameters are enclosed in angle brackets
Placed after the name of the class
Type parameter declares variables and generic methods within the class
modifiers className<T> modifiers {
//class members }
Also known as parametric classes
Java Programming: Guided Learning with Early Objects

7. Generic Classes (continued)
Reference variables declared using type parameter T within definition of the class
Cannot instantiate objects using type parameter
Java Programming: Guided Learning with Early Objects

8. The interface Comparable
One method: compareTo
Used to require a class to provide definition for the method compareTo
Allows values of two objects to be compared
Make the class implement interface Comparable
Java Programming: Guided Learning with Early Objects

9. Generic Methods and Bounded Type Parameters
Recall generic method print
Type parameter T refers to any built-in Java class
No restriction on type parameter T
Type parameters restricted, for example, to classes that define compareTo
Example:
public static <T extends Comparable<T>> T
larger( T x, T y )
Java Programming: Guided Learning with Early Objects

10. Generic Methods and Bounded Type Parameters (continued)
Consider:
<T extends Comparable<T>>
T refers to any class that implements Comparable
Comparable is the upper bound of the type parameter T
By default, Object always an upper bound
Keyword extends used when type parameter declaration bounds a parameter
Java Programming: Guided Learning with Early Objects

11. Generic Search and Sort Algorithms (Optional)
Sort algorithms from earlier chapters work only on int arrays
Designing generic search and sort algorithms
Generic selection sort
Place definition of selection algorithm in a class
Java Programming: Guided Learning with Early Objects

12. Collections Vector known as a collection class
class Vector implements array-based lists
class LinkedList implements a linked list
Java Programming: Guided Learning with Early Objects

13. Linked Lists and the class LinkedList
Array also called a sequential list
Operations on sequential lists:
Insertion
Deletion
Searching
Searching unsorted data is time-consuming
Insertion and deletion is time-consuming on sorted lists
Array size is fixed
Java Programming: Guided Learning with Early Objects

14. Linked Lists Linked list: collection of components called nodes
Each node contains address of next node
Two parts:
One stores relevant information
One stores address
Address of first node is called head or first
class Node defines the node of a linked list
Two instance variables: info and link
Java Programming: Guided Learning with Early Objects

15. Figure 12-3 Linked list and values of the links
Java Programming: Guided Learning with Early Objects

16. Linked Lists: Some Properties
Keep a reference variable current to point to address of the current node in the list
Useful for traversing the list
Java Programming: Guided Learning with Early Objects

17. Figure 12-4 Linked list with four nodes
Java Programming: Guided Learning with Early Objects

18. Table 12-1 Values of head and Some of the Nodes of the Linked List in Figure 12-4
Java Programming: Guided Learning with Early Objects

19. Figure 12-5 Linked list after the statement current = current
Figure 12-5 Linked list after the statement current = current.link; executes
Java Programming: Guided Learning with Early Objects

20. Table 12-2 Values of current and Some of the Nodes of the Linked List in Figure 12-5
Java Programming: Guided Learning with Early Objects

21. Insertion Create a new node Store data in instance variable info
Set instance variable link to point to following node
Set previous node variable link to point to new node
Java Programming: Guided Learning with Early Objects

22. Figure 12-6 Linked list before item insertion
Java Programming: Guided Learning with Early Objects

23. Figure 12-7 Create newNode and store 50 in it
Java Programming: Guided Learning with Early Objects

24. Figure 12-8 List after the statement newNode.link = p.link; executes
Java Programming: Guided Learning with Early Objects

25. Figure 12-9 List after the statement p.link = newNode; executes
Java Programming: Guided Learning with Early Objects

26. Deletion
Set link variable of previous node to link to next node in list
Bypass the node to be deleted
Garbage collector runs if no reference variable points to the deleted node
Memory reclaimed by system
Java Programming: Guided Learning with Early Objects

27. Figure 12-10 Node to be deleted is with info 34
Java Programming: Guided Learning with Early Objects

28. Figure 12-11 List after the statement p.link = p.link.link; executes
Java Programming: Guided Learning with Early Objects

29. Doubly Linked Lists
Every node has a next pointer and a previous pointer
Can be traversed efficiently in either direction
Can traverse from first or last node
Inserting a node requires setting pointers in both directions
Deleting a node requires bypassing a node in both directions
Java Programming: Guided Learning with Early Objects

30. Figure 12-12 Doubly linked list
Java Programming: Guided Learning with Early Objects

31. The class LinkedList
class LinkedList implemented as a doubly linked list
Every element points to immediate predecessor and successor
Two constructors:
Collection<? extends E>
Type parameter ? represents unknown type
? called wildcard
Type E an upper bound of the wildcard
Java Programming: Guided Learning with Early Objects

32. Iterators Process elements of a collection one by one Use an iterator
Could use foreach loop
Use an iterator
Processes elements in collection one after the other
interface ListIterator implements interface Iterator
interface Iterator has only three methods
Java Programming: Guided Learning with Early Objects

33. Table 12-4 Methods of the interface Iterator
Java Programming: Guided Learning with Early Objects

34. Table 12-5 The interface ListIterator and its Methods
Java Programming: Guided Learning with Early Objects

35. Table 12-5 The interface ListIterator and its Methods (continued)
Java Programming: Guided Learning with Early Objects

36. Iterators (continued)
Typically, iterator moves in only one direction
Starts at first element, moves to last
class LinkedList implemented as doubly linked lists
Iterator should move in both directions
interface ListInterface extends interface Iterator
Has methods to move in both directions
Can also be used for insertion and deletion
Java Programming: Guided Learning with Early Objects

37. Collections and Collection Algorithms
Collection: data structure that holds references to other objects
Examples: vector, array
Collection class: a class whose objects are collections
Example: class Vector
Several interfaces and classes implement collections systematically
Hierarchical structure
Java Programming: Guided Learning with Early Objects

38. Figure 12-13 Some Java Collection classes and the inheritance hierarchy
Java Programming: Guided Learning with Early Objects

39. Table 12-6 Methods of the Collections class
Java Programming: Guided Learning with Early Objects

40. The Method addAll
Method addAll adds the elements of a collection into another collection
List to be added is a variable length parameter
Elements specified individually or as an array
Throws: UnsupportedOperationException, NullPointerException, IllegalArgumentException
Java Programming: Guided Learning with Early Objects

41. The Methods binarySearch, sort, and reverseOrder
binarySearch: search the list, specified as parameter for object
Efficiently searches a list for a given element
Requires a list to be sorted
List can be sorted in ascending or descending order using reverseOrder
sort: type parameter T bounded by interface Comparable
Java Programming: Guided Learning with Early Objects

42. Table 12-7 Methods of the interface Comparator
Java Programming: Guided Learning with Early Objects

43. The Method copy
Copies elements of one collection into another collection object
After copy operation, index of each copied element is identical in source and destination
Copies only references of the objects
Objects in destination list point to same objects as source
Objects in source list are mutable
Changing value of object by using source changes value in destination
Java Programming: Guided Learning with Early Objects

44. The Methods max and min
Methods max and min determine maximum and minimum elements
All elements in collection must be mutually comparable by the comparator
Throws exceptions:
ClassCastException
NoSuchElementException
Java Programming: Guided Learning with Early Objects

45. The Methods fill and frequency
Method fill replaces all elements of a given list with given element
Type parameter T specifies type of list elements as well as type of replacement element
Method frequency finds the number of times a specific object appears in a collection
If collection is null, throws NullPointerException
Java Programming: Guided Learning with Early Objects

46. The Method replaceAll
Replaces all occurrences of a given element with another
Type parameter T specifies type of list elements
Returns true if list contains one or more elements equal to replacement object
If list or list iterator does not support set method, throws exception
Java Programming: Guided Learning with Early Objects

47. The Methods shuffle and swap
Method shuffle randomly shuffles elements of a list
Two forms: with and without random seed
All permutations occur with approximately equal likelihood
Method swap swaps elements of list
Java Programming: Guided Learning with Early Objects

48. Summary Generic methods are defined using type parameters
Every generic method has a type parameter section preceding the return type of the method
Type parameters separated by commas
Enclosed in angle brackets
Type parameters specify generic type names
Within generic method, declare reference variables using type parameter T
Java Programming: Guided Learning with Early Objects

49. Summary (continued) Type parameter may be bounded or unbounded
Cannot instantiate objects using type parameter
class LinkedList implemented as a doubly linked list
Contained in package java.util
The foreach loop iterates over LinkedList
Iterator iterates over elements of a collection
Java Programming: Guided Learning with Early Objects

50. Summary (continued)
Collection is a data structure that holds references to objects
Collection class is a class whose objects are collections
interface Collection is the superclass of all Java collection classes
Generic algorithms designed as static methods of class Collections
Java Programming: Guided Learning with Early Objects