1. Iterators (short version)
Chapter 15
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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?
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Objectives
Describe concept of iterator
Use iterator to traverse, manipulate a list
Implement in Java inner class iterator for list
Describe pros of inner class iterators
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What Is an Iterator?
Program component
Enables you to step through, or
Traverse, a collection of data
During a traversal
Each data item considered once
When we write loops
They traverse, iterate through whole list
Consider interface Iterator, Listing 15-1
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5. Using the Interface Iterator
Implement iterator methods within their own class
Can be private, separate from ADT class
Or private, inner class of ADT
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6. Using iterators nameList nameIterator Maha Nadia Rehab
ListWithIteratorInterface <String> nameList = new ArrayListWithIterator <String>(); nameList.add(“Maha”); nameList.add(“Nadia”); nameList.add(“Rehab”); Iterator < String > nameIterator = nameList.getIterator(); nameIterator.remove(); if(nameIterator.hasNext();) nameIterator.next(); System.out.println (nameIterator.next());
nameList
nameIterator
Maha
Nadia
Rehab
IllegalStateException
As we go through this example, ask the students to look at the interface for iterators.
Q - At the first remove, ask students they can predict what will happen.
A - exception
Q - Then ask them why it happened
A - we did not call next() yet.
At the second remove statement, point out that a call to next should give us “Rehab”, we have to make sure in our implementation that that will be the case.
Ask the students where they think the arrow will be after removal? Only then click for next slide!!
Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved X

7. Using iterators nameList nameIterator Maha Rehab
ListWithIteratorInterface <String> nameList = new LinkedListWithIterator <String>(); nameList.add(“Maha”); nameList.add(“Nadia”); nameList.add(“Rehab”); Iterator < String > nameIterator = nameList.getIterator(); nameIterator.remove(); if(nameIterator.hasNext();) nameIterator.next(); System.out.println (nameIterator.next()); nameList.display();
nameList
nameIterator
Maha
Rehab
Carrano, Data Structures and Abstractions with Java, Second Edition, (c) 2007 Pearson Education, Inc. All rights reserved X

8. Copyright ©2012 by Pearson Education, Inc. All rights reserved
End
Chapter 15
Copyright ©2012 by Pearson Education, Inc. All rights reserved