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IteratorExample1/src/Alphabet.java
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193
IteratorExample1/src/Alphabet.java
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import java.util.NoSuchElementException;
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/**
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*
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* @author latimer
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* @version 1.00 03/03/16
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*
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* Example of an Iterator for the LinkedPositionalList class.
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*
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*/
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public class Alphabet {
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private LinkedPositionalList<Letter> alphabet = null;
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//
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// Constructor builds a LinkedPositionalList of Letters.
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//
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public Alphabet( ){
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alphabet = new LinkedPositionalList<>();
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String alphabetString = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
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Letter nextLetter;
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for ( int i = 0; i < alphabetString.length(); i++ )
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{
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nextLetter = new Letter( alphabetString.charAt(i) );
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alphabet.addLast( nextLetter );
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}
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}
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public boolean isVowel( String s )
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{
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return ( s.equals("A") || s.equals("E") || s.equals("I") || s.equals("O") || s.equals("U") );
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}
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//
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// This method uses an iterator to traverse the list.
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//
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// Note that here we are using the nested iterator classes from the
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// LinkedPositionalList class and not ones for the Alphabet class.
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//
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@Override
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public String toString( )
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{
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String returnString = "";
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Iterator<Letter> listIterator = alphabet.iterator();
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while ( listIterator.hasNext() )
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returnString += listIterator.next() + " ";
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return returnString;
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}
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//
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// The following classes are the nested Iterator classes from
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// Code Fragment 7.14
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//
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// Only the classes for the Position Itertor have bee included.
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//
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// These fragements have been modified so that they are specific to the
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// Alphabet class.
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//
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// It is necessary to put the iterator code here since we want to create
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// iterators specifically for the Alphabet class which is a concrete class
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// based on the generic ADT LinkedPositionalList.
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//
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// Our code needs to have knowledge of Letter.
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//
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// Generally the Generic placeholders <E> have been replaced with
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// concret references <Letter>
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// AND
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// Call to LinkedPositionalList methods have be replaced by calls using
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// the instance reference alphabet
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// e.g.
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// private Position<Letter> cursor = first();
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// became
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// private Position<Letter> cursor = alphabet.first();
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//
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//----- nested PositionIterator class -----
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private class PositionIterator implements Iterator<Position<Letter>>{
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private Position<Letter> cursor = alphabet.first(); // position of the next element to report
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private Position<Letter> recent = null; // position of last reported element
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/** Tests whether the iterator has a next object. */
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@Override
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public boolean hasNext( ) { return ( cursor != null ); }
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/** Returns the next position in the iterator. */
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@Override
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public Position<Letter> next( ) throws NoSuchElementException {
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if ( cursor == null ) throw new NoSuchElementException( "nothing left " );
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recent = cursor;
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cursor = alphabet.after( cursor );
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return recent;
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}
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/** Removes the element returned by most recent call to next. */
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@Override
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public void remove( ) throws IllegalStateException {
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if ( recent == null ) throw new IllegalStateException( "nothing to remove" );
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alphabet.remove( recent ); // remove from outer list
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recent = null; // do not allow remove again until next is called
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}
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} //----- end of nested PositionIterator class -----
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//----- nested PositionIterable class -----
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private class PositionIterable implements Iterable<Position<Letter>>{
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@Override
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public Iterator<Position<Letter>> iterator( ) { return new PositionIterator( ); }
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} //----- end of nested PositionIterable class -----
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/** Returns an iterable representation of the list's positions.
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* @return */
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public Iterable<Position<Letter>> positions( ) {
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return new PositionIterable( ); // create a new instace of the inner class
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}
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//
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// Below are the nested iterator classes modified to iterate over just the
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// vowels in a the alphabet list
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//
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// Aside from taking care of name conflicts the only real modification
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// that is necessary is in the next() method betweeen the lines:
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// recent = cursor;
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// << modification goes here
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// return recent;
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//
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// This is because cursor points to the Position that will be returned
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// the "next" time next() is called so:
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// after saving the value of cursor to recent
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// cursor is advanced to the next desired location
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// -- you customize where the cursor is advanced to.
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// then the value of recent is returned.
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//
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// You can create additional custom iterators by making additional copies
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// of the nested iterator classes, adjusting the names, and modifying
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// how the value of cursor is updated on each call to next().
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//
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//----- nested PositionIterator class -----
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private class VowelPositionIterator implements Iterator<Position<Letter>>{
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private Position<Letter> cursor = alphabet.first(); // position of the next element to report
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private Position<Letter> recent = null; // position of last reported element
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/** Tests whether the iterator has a next object. */
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@Override
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public boolean hasNext( ) { return ( cursor != null ); }
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/** Returns the next position in the iterator. */
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@Override
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public Position<Letter> next( ) throws NoSuchElementException {
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// On the first call to next (i.e. when recent == null) you need to //<<< new code
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// advance recent until it is pointing to a vowel element. //<<< new code
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if ( recent == null ) //<<< new code
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{ //<<< new code
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while ( cursor != null && !isVowel( cursor.getElement().letter) ) //<<< new code
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cursor = alphabet.after( cursor ); //<<< new code
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} //<<< new code
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if ( cursor == null ) throw new NoSuchElementException( "nothing left " );
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recent = cursor;
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cursor = alphabet.after( cursor );
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// advance cursor to the next vowel
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while ( cursor != null && !isVowel( cursor.getElement().letter) )
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cursor = alphabet.after( cursor );
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return recent;
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}
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/** Removes the element returned by most recent call to next. */
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@Override
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public void remove( ) throws IllegalStateException {
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if ( recent == null ) throw new IllegalStateException( "nothing to remove" );
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alphabet.remove( recent ); // remove from outer list
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recent = null; // do not allow remove again until next is called
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}
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} //----- end of nested PositionIterator class -----
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//----- nested PositionIterable class -----
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private class VowelPositionIterable implements Iterable<Position<Letter>>{
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@Override
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public Iterator<Position<Letter>> iterator( ) { return new VowelPositionIterator( ); }
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} //----- end of nested PositionIterable class -----
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/** Returns an iterable representation of the list's positions.
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* @return */
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public Iterable<Position<Letter>> vowelPositions( ) {
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return new VowelPositionIterable( ); // create a new instace of the inner class
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}
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}
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