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Iterators Chapter 8 Slides by Steve Armstrong LeTourneau University Longview, TX  2007,  Prentice Hall.

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Presentation on theme: "Iterators Chapter 8 Slides by Steve Armstrong LeTourneau University Longview, TX  2007,  Prentice Hall."— Presentation transcript:

1 Iterators Chapter 8 Slides by Steve Armstrong LeTourneau University Longview, TX  2007,  Prentice Hall

2 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Chapter Contents What is an Iterator ? The Interface Iterator  Using the Interface Iterator An Inner Class Iterator  A Linked Implementation  An Array-Based Implementation Why Are Iterator Methods in Their Own Class?

3 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Chapter Contents The Interface ListIterator  Using the Interface ListIterator An Array-Based Implementation of the Interface ListIterator  The Inner Class Java Class Library: The Interface Iterable Iterable and for-each Loops The Interface List Revisited

4 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X What Is an Iterator? 1 A program component  Enables you to step through, traverse a collection of data  Can tell whether next entry exists Iterator may be manipulated  Asked to advance to next entry  Give a reference to current entry  Modify the list as you traverse it

5 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface Iterator 3 Found in java.util in Java Class Library One of two iterator classes View source code of interface IteratorView source code  Specifies a generic type for entries Note three methods  Method hasNext  Method next  Method remove

6 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface Iterator 4 Position of an iterator is not at an entry  Positioned either before first entry  Or between two entries Fig 8-1 The effect of a call to next on a list iterator

7 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface Iterator 6 Consider a list of names created with the code below (from chap 6) Then create a separate class iterator

8 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface Iterator Fig. 8-2 The effect of iterator methods on a list.

9 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface Iterator Now execute several commands for illustration

10 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface Iterator 7 Fig. 8-3 The effect of the iterator methods next and remove on a list

11 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Multiple Iterators 10 Possible to have several iterators of the same list View sample codeView sample code Fig 8-4 Counting the number of times that Jane appears in a list of names

12 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Class SeparateIterator 12 Used to connect an iterator with a list  Invoke SeparateIterator constructor View source code of SeparateIteratorView source code  Note data field that references list  Note the class is independent of how the list is implemented – use ListInterface Note methods  hasNext hasNext  next next  remove remove

13 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Class SeparateIterator Fig. 8-6 A list and nextPosition (a) just before the call to next ;

14 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Class SeparateIterator Fig. 8-6 A list and nextPosition (b) just after the call to next but before the call to remove ;

15 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Class SeparateIterator Fig. 8-6 A list and nextPosition (c) after the call to remove

16 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Inner Class Iterator 16 An alternative to separate class iterators Define the iterator class as an inner class of the ADT  Multiple iterations possible  Has direct access to ADT's data fields as inner class Required interface – Listing 8-3

17 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Inner Class Iterator 17 View class LinkedListWithIteratorView class Note methods declared in interface Iteratormethods declared in interface  Found within inner class IteratorForLinkedList  This inner class has data field nextNode to track an iteration  nextNode references the node that method next must access

18 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Inner Class Iterator 20 Fig. 8-7 An inner class iterator with direct access to the linked chain that implements the ADT

19 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Array-Based Implementation 24 View outline of ArrayListWithIteratorView outline Note methods required for the inner classinner class  hasNext  next  remove

20 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Array-Based Implementation 28 Fig 8-8 The array of list entries and nextIndex (a) just before to the call to next

21 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Array-Based Implementation Fig 8-8 The array of list entries and nextIndex (b) just after the call to next but before the call to remove

22 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X An Array-Based Implementation Fig 8-8 The array of list entries and nextIndex (c) after the call to remove

23 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Why are Iterator Methods in Their Own Class? 29 Consider modification of linked implementations of list  Include the methods specified in Java interface Iterator  Method remove not included for simplicity View outline of ListWithTraversalListWithTraversal  Note similarities and differences with Listing 8-4 Listing 8-4

24 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Why are Iterator Methods in Their Own Class? 30 Note that traversal methods do execute quickly  Direct access to underlying data structure But …  Only one traversal can be in progress at a time  Resulting ADT requires too many operations (interface bloat)

25 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface ListIterator 32 An alternative interface for iterators in Java Class Library Enables traversal in either direction Allows modification of list during iteration View interface java.util.ListIteratorView interface Note methods  hasPrevious  previous  add  set

26 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface ListIterator 35 Fig. 8-9 The effect of a call to previous on a list

27 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface ListIterator 36 Fig. 8-10 The indices returned by the methods nextIndex and previousIndex

28 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface ListIterator 37 Assuming  The interface ListIterator implemented as an inner class which implements ADT list  Iterator includes methods add, remove, set  Method getIterator added to ADT list  List called nameList, contains 3 names  Iterator traverse

29 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Using the Interface ListIterator 37 Note sample commands and output

30 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator 41 First define an interface withdefine an interface  Operations from ADT list  Method getIterator Now define the class that implements the ADT listdefine the class  Same data fields and methods as version of AList from chapter 5 AList  Note inner class IteratorForArrayList implements ListIterator

31 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator 43 Fig. 8-11 Possible contexts in which the method remove throws an exception when called by the iterator traverse

32 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator Fig. 8-11 Possible contexts in which the method remove throws an exception when called by the iterator traverse

33 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator 48 Fig. 8-12 The array of list entries and nextIndex (a) just before the call to add ; (b) just after the call to add

34 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator 49 Fig. 8-13 The array of list entries and nextIndex (a) just before the call to previous

35 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator Fig. 8-13 The array of list entries and nextIndex (b) just after the call to previous but before the call to remove

36 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Array-Based Implementation of ListIterator Fig. 8-13 The array of list entries and nextIndex (c) after the call to remove

37 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Java Class Library: The Interface Iterable 51 Consider Listing 8-10 The interface java.lang.Iterable Method has same purpose as previous method getIterator Method has same purpose as previous method getIterator

38 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Java Class Library: The Interface Iterable Listing 8-11 The interface ListWithIteratorInterface modified to extend Iterable

39 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X Iterable and for-each Loops 52 Class which implements Iterable has distinct advantage Able to use a for-each loop to traverse objects in an instance of the class

40 Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved. 0-13-237045-X The Interface List Revisited 53 Recall interface java.util.List from segment 4.19 of Chapter 4 It extends Iterable  Thus has method iterator Also has methods

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