COMPUTER 2430 Object Oriented Programming and Data Structures I

Containers Bag Set Stack Queue Sorted List . . . Array Linked List

Iterators Step through a container Array Circular array Sorted Array Linked List Without knowing the details of the container For users to use

Why Iterators? public class StudentList { . . . public float avgGPA() . . } After the class is completed, the application wants to know the average score for the final exam of CS 2430 Modify class StudentList The application utilizes an Iterator if it’s implemented!

Java Iterator Interface // Only two methods public Interface Iterator { // The class implementing the interface should have // a pointer to the next object in the container // Returns true if next() can be successfully called public boolean hasNext(); // Returns the next object and // moves the pointer to the following object public Object next(); }

Different Types of Iterators External Internal Embedded

External Iterators import java.util.Iterator; public class List { . . . . . } public class MyIter implements Iterator Advantage Can have several iterators over the same container at the same time Disadvantage The iterator class needs to get at the details of the container class.

Internal Iterators import java.util.Iterator; public class List implements Iterator { . . . . . } Advantage Direct access to the container class. Disadvantage Can have only one iterator over the same container at one time

Embedded Iterators import java.util.Iterator; public class List { . . . . . public static class ListIterator implements Iterator } Combine the advantages of internal and external iterators Direct access to the container class. Can have several iterators over the same container at the same time

Embedded Iterators on Array public class List { private Object [] elements; private int num; public List ( int initialSize ) elements = new Object[ initialSize ]; num = 0; } .... All the other nice list methods .... could be growable public static class ListIterator implements Iterator . . . . .

private Object [] elements; // regular array, not circular public class List { private Object [] elements; // regular array, not circular private int num; public static class ListIterator implements Iterator private List theList; private int index; // index of the next object   public ListIterator ( List list ) theList = list; index = 0; } @Override public boolean hasNext() return index < theList.num; public Object next() return theList.elements[index ++];

Example List myList = new List(1000); ...... Iterator iter = new List.ListIterator(myList); while ( iter.hasNext() ) System.out.println ( iter.next() );

Generic Iterator Interface // Only two methods public Interface Iterator<E> { // The class implementing the interface should have // a pointer to the next object in the container // Returns true if next() can be successfully called public boolean hasNext(); // Returns the next object and // moves the pointer to the following object public E next(); }

Prog 3: FixedPointList public class FixedPointList { private static final int GROWBY = 3; private int num = 0; private FixedPoint[] list = new FixedPoint[GROWBY]; public FixedPoint min() public FixedPoint max() public FixedPoint sum(int q) . . . }

public class FixedPointList { private int num = 0; private FixedPoint[] list = new FixedPoint[GROWBY]; . . . public static class MyIterator implements Iterator<FixedPoint> private FixedPointList theList; private int index; public MyIterator(FixedPointList list) theList = list; index = 0; } @Override public boolean hasNext() return index < theList.num; public FixedPoint next() return theList.list[index ++];

public class Prog3 { private static FixedPointList list = new FixedPointList(); . . . private static void sumCmd() FixedPointList.MyIterator iterator = new FixedPointList.MyIterator(list); FixedPoint fp = new FixedPoint(0.0, curQ); while(iterator.hasNext()) fp = fp.plus(iterator.next(), curQ); System.out.println("The sum is: " + fp); }

private Object [] elements; public class Queue { private Object [] elements; private int front, rear, count; // circular array public static class QueueIterator implements Iterator private Queue theQueue; private int index; // index of the next object   public QueueIterator ( Queue queue ) theQueue = queue; index = ??? } @Override public boolean hasNext() return ??? public Object next()

public class Final { private static Queue myQueue = new Queue(1000); public class Final { private static Queue myQueue = new Queue(1000); . . . private static void sumCmd() Queue.QueueIterator iterator = new Queue.QueueIterator(myQueue); FixedPoint fp, sum = new FixedPoint(0.0, curQ); while(iterator.hasNext()) fp = (FixedPoint)iterator.next(); sum = sum.plus(fp, curQ); } System.out.println("The sum is: " + fp);

Test 3 Wednesday, Dec 12 Please Fill out the Course Outcome Survey! Schedule Test 3 Wednesday, Dec 12 Please Fill out the Course Outcome Survey!

Test 3 Big O Counting Sorting Hashing Binary Search LSP (Iterator will be on the final exam)

Prog 6