Java/Design Pattern/Iterator Pattern

Iterator Pattern 3

   <source lang="java">

//[C] 2002 Sun Microsystems, Inc.--- import java.io.File; import java.io.FileInputStream; import java.io.FileOutputStream; import java.io.IOException; import java.io.ObjectInputStream; import java.io.ObjectOutputStream; import java.io.PrintStream; import java.io.Serializable; import java.util.ArrayList; import java.util.HashMap; import java.util.Iterator; import java.io.File; import java.io.IOException; public class RunIteratorPattern {

   public static void main(String [] arguments){
       System.out.println("Example for the Iterator pattern");
       System.out.println(" This code sample demonstrates how an Iterator can enforce");
       System.out.println(" uniformity of processing for different collection types.");
       System.out.println(" In this case, there are two classes, ToDoListImpl and");
       System.out.println(" ToDoListCollectionImpl, that have different storage needs.");
       System.out.println(" ToDoListImpl uses an ArrayList to store its elements in");
       System.out.println(" ordered form. The ToDoListCollectionImpl uses a HashMap,");
       System.out.println(" since it must differentiate between ToDoListImpl objects by");
       System.out.println(" their String identifiers.");
       System.out.println();
       System.out.println("Although the two classes use different underlying collections,");
       System.out.println(" the ListPrinter class can use the Iterator produced by each");
       System.out.println(" to print out a set of list contents.");
       System.out.println();
       
       if (!(new File("data.ser").exists())){
           DataCreator.serialize("data.ser");
       }
       ToDoListCollection lists = (ToDoListCollection)(DataRetriever.deserializeData("data.ser"));
       
       System.out.println("Lists retrieved. Printing out contents using the Iterator");
       System.out.println();
       ListPrinter.printToDoListCollection(lists, System.out);
   }

} interface Iterating extends Serializable {

 public Iterator getIterator();

} class ToDoListImpl implements ToDoList {

 private String listName;
 private ArrayList items = new ArrayList();
 public void add(String item) {
   if (!items.contains(item)) {
     items.add(item);
   }
 }
 public void add(String item, int position) {
   if (!items.contains(item)) {
     items.add(position, item);
   }
 }
 public void remove(String item) {
   if (items.contains(item)) {
     items.remove(items.indexOf(item));
   }
 }
 public int getNumberOfItems() {
   return items.size();
 }
 public Iterator getIterator() {
   return items.iterator();
 }
 public String getListName() {
   return listName;
 }
 public void setListName(String newListName) {
   listName = newListName;
 }
 public String toString() {
   return listName;
 }

} interface ToDoListCollection extends Iterating {

 public void add(ToDoList list);
 public void remove(ToDoList list);
 public int getNumberOfItems();

} interface ToDoList extends Iterating {

 public void add(String item);
 public void add(String item, int position);
 public void remove(String item);
 public int getNumberOfItems();
 public String getListName();
 public void setListName(String newListName);

} class ListPrinter {

 public static void printToDoList(ToDoList list, PrintStream output) {
   Iterator elements = list.getIterator();
   output.println("  List - " + list + ":");
   while (elements.hasNext()) {
     output.println("\t" + elements.next());
   }
 }
 public static void printToDoListCollection(ToDoListCollection lotsOfLists,
     PrintStream output) {
   Iterator elements = lotsOfLists.getIterator();
   output.println("\"To Do\" List Collection:");
   while (elements.hasNext()) {
     printToDoList((ToDoList) elements.next(), output);
   }
 }
 public static void printIteratingElement(Iterating element,
     PrintStream output) {
   output.println("Printing the element " + element);
   Iterator elements = element.getIterator();
   while (elements.hasNext()) {
     Object currentElement = elements.next();
     if (currentElement instanceof Iterating) {
       printIteratingElement((Iterating) currentElement, output);
       output.println();
     } else {
       output.println(currentElement);
     }
   }
 }

} class DataRetriever {

 public static Object deserializeData(String fileName) {
   Object returnValue = null;
   try {
     File inputFile = new File(fileName);
     if (inputFile.exists() && inputFile.isFile()) {
       ObjectInputStream readIn = new ObjectInputStream(
           new FileInputStream(fileName));
       returnValue = readIn.readObject();
       readIn.close();
     } else {
       System.err.println("Unable to locate the file " + fileName);
     }
   } catch (ClassNotFoundException exc) {
     exc.printStackTrace();
   } catch (IOException exc) {
     exc.printStackTrace();
   }
   return returnValue;
 }

} class ToDoListCollectionImpl implements ToDoListCollection {

 private HashMap lists = new HashMap();
 public void add(ToDoList list) {
   if (!lists.containsKey(list.getListName())) {
     lists.put(list.getListName(), list);
   }
 }
 public void remove(ToDoList list) {
   if (lists.containsKey(list.getListName())) {
     lists.remove(list.getListName());
   }
 }
 public int getNumberOfItems() {
   return lists.size();
 }
 public Iterator getIterator() {
   return lists.values().iterator();
 }
 public String toString() {
   return getClass().toString();
 }

} class DataCreator {

 private static final String DEFAULT_FILE = "data.ser";
 public static void main(String[] args) {
   String fileName;
   if (args.length == 1) {
     fileName = args[0];
   } else {
     fileName = DEFAULT_FILE;
   }
   serialize(fileName);
 }
 public static void serialize(String fileName) {
   try {
     serializeToFile(createData(), fileName);
   } catch (IOException exc) {
     exc.printStackTrace();
   }
 }
 private static Serializable createData() {
   ToDoListCollection data = new ToDoListCollectionImpl();
   ToDoList listOne = new ToDoListImpl();
   ToDoList listTwo = new ToDoListImpl();
   ToDoList listThree = new ToDoListImpl();
   listOne.setListName("Daily Routine");
   listTwo.setListName("Programmer hair washing procedure");
   listThree.setListName("Reading List");
   listOne.add("Get up (harder some days than others)");
   listOne.add("Brew cuppa Java");
   listOne.add("Read JVM Times");
   listTwo.add("Lather");
   listTwo.add("Rinse");
   listTwo.add("Repeat");
   listTwo.add("(eventually throw a TooMuchHairConditioner exception)");
   listThree.add("The complete annotated aphorisms of Duke");
   listThree.add("How green was my Java");
   listThree.add("URL, sweet URL");
   data.add(listOne);
   data.add(listTwo);
   data.add(listThree);
   return data;
 }
 private static void serializeToFile(Serializable data, String fileName)
     throws IOException {
   ObjectOutputStream serOut = new ObjectOutputStream(
       new FileOutputStream(fileName));
   serOut.writeObject(data);
   serOut.close();
 }

}

      </source>
   
  
 
  

Iterator pattern in Java

   <source lang="java">

/* The Design Patterns Java Companion Copyright (C) 1998, by James W. Cooper IBM Thomas J. Watson Research Center

• /

import java.awt.BorderLayout; import java.awt.Dimension; import java.awt.GridLayout; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.WindowAdapter; import java.awt.event.WindowEvent; import java.io.IOException; import java.io.RandomAccessFile; import java.util.Enumeration; import java.util.NoSuchElementException; import java.util.StringTokenizer; import java.util.Vector; import javax.swing.AbstractListModel; import javax.swing.JButton; import javax.swing.JFrame; import javax.swing.JList; import javax.swing.JPanel; import javax.swing.JScrollPane; import javax.swing.JTextField; import javax.swing.border.EmptyBorder; import javax.swing.event.ListSelectionEvent; import javax.swing.event.ListSelectionListener; public class IterDemo extends JFrame implements ActionListener {

 JawtList kidList, kidClubList;
 JTextField tx;
 JButton Get;
 KidData kdata;
 public IterDemo() {
   super("Enumeration demo");
   addWindowListener(new WindowAdapter() {
     public void windowClosing(WindowEvent e) {
       System.exit(0);
     }
   });
   JPanel jp = new JPanel();
   getContentPane().add(jp);
   jp.setLayout(new GridLayout(1, 2));
   JPanel left = new JPanel();
   JPanel right = new JPanel();
   jp.add(left);
   jp.add(right);
   left.setBorder(new EmptyBorder(5, 5, 5, 5));
   right.setBorder(new EmptyBorder(5, 5, 5, 5));
   kidList = new JawtList(20);
   left.setLayout(new BorderLayout());
   left.add("Center", kidList);
   right.setLayout(new BorderLayout());
   tx = new JTextField(10);
   Get = new JButton("Get");
   Get.addActionListener(this);
   JPanel rtop = new JPanel();
   right.add("North", rtop);
   rtop.add(tx);
   rtop.add(Get);
   kidClubList = new JawtList(20);
   right.add("Center", kidClubList);
   kdata = new KidData("50free.txt");
   fillKidList();
   setSize(new Dimension(400, 300));
   setVisible(true);
 }
 //---------------------------------------
 private void fillKidList() {
   Enumeration ekid = kdata.elements();
   while (ekid.hasMoreElements()) {
     Kid k = (Kid) ekid.nextElement();
     kidList.add(k.getFrname() + " " + k.getLname());
   }
 }
 //---------------------------------------
 public void actionPerformed(ActionEvent e) {
   String club = tx.getText();
   if (club.trim().length() > 0) {
     Enumeration eclub = kdata.kidsInClub(club);
     while (eclub.hasMoreElements()) {
       Kid k = (Kid) eclub.nextElement();
       kidClubList.add(k.getFrname() + " " + k.getLname());
     }
   }
 }
 //---------------------------------------
 static public void main(String argv[]) {
   new IterDemo();
 }

} interface awtList {

    public void add(String s);
    public void remove(String s);
    public String[] getSelectedItems();

}

class JawtList extends JScrollPane implements ListSelectionListener, awtList {

 private JList listWindow;
 private JListData listContents;
 //-----------------------------------------
 public JawtList(int rows) {
   listContents = new JListData();
   listWindow = new JList(listContents);
   listWindow.setPrototypeCellValue("Abcdefg Hijkmnop");
   getViewport().add(listWindow);
 }
 //-----------------------------------------
 public void add(String s) {
   listContents.addElement(s);
 }
 //-----------------------------------------
 public void remove(String s) {
   listContents.removeElement(s);
 }
 //-----------------------------------------
 public void clear() {
   listContents.clear();
 }
 //-----------------------------------------
 public String[] getSelectedItems() {
   Object[] obj = listWindow.getSelectedValues();
   String[] s = new String[obj.length];
   for (int i = 0; i < obj.length; i++)
     s[i] = obj[i].toString();
   return s;
 }
 //-----------------------------------------
 public void valueChanged(ListSelectionEvent e) {
 }

} //========================================= class JListData extends AbstractListModel {

 private Vector data;
 //-----------------------------------------
 public JListData() {
   data = new Vector();
 }
 //-----------------------------------------
 public int getSize() {
   return data.size();
 }
 //-----------------------------------------
 public Object getElementAt(int index) {
   return data.elementAt(index);
 }
 //-----------------------------------------
 public void addElement(String s) {
   data.addElement(s);
   fireIntervalAdded(this, data.size() - 1, data.size());
 }
 //-----------------------------------------
 public void removeElement(String s) {
   data.removeElement(s);
   fireIntervalRemoved(this, 0, data.size());
 }
 //-----------------------------------------
 public void clear() {
   int size = data.size();
   data = new Vector();
   fireIntervalRemoved(this, 0, size);
 }

} class KidData {

 Vector kids;
 //------------------------------------------
 public KidData(String filename) {
   kids = new Vector();
   InputFile f = new InputFile(filename);
   String s = f.readLine();
   while (s != null) {
     if (s.trim().length() > 0) {
       Kid k = new Kid(s);
       kids.addElement(k);
     }
     s = f.readLine();
   }
 }
 //--------------------------------
 public Kid[] getData() {
   Kid[] kd = new Kid[kids.size()];
   for (int i = 0; i < kids.size(); i++)
     kd[i] = (Kid) kids.elementAt(i);
   return kd;
 }
 //--------------------------------
 public Enumeration elements() {
   return kids.elements();
 }
 //-------------------------------
 public Enumeration kidsInClub(String club) {
   return new kidClub(this, club);
 }
 //--------------------------------
 public int size() {
   return kids.size();
 }
 //--------------------------------
 public Kid getKid(int i) {
   return (Kid) kids.elementAt(i);
 }
 //--------------------------------
 public Vector getKidData(int key) {
   Vector v = new Vector();
   for (int i = 0; i < kids.size(); i++)
     v.addElement(getKid(i).getData(key));
   return v;
 }
 //--------------------------------
 public int getTableKey(String tabName) {
   int key = -1;
   tabName = tabName.toLowerCase();
   if (tabName.equals("frname"))
     key = ParseVar.FRNAME;
   if (tabName.equals("lname"))
     key = ParseVar.LNAME;
   if (tabName.equals("age"))
     key = ParseVar.AGE;
   if (tabName.equals("club"))
     key = ParseVar.CLUB;
   if (tabName.equals("time"))
     key = ParseVar.TIME;
   return key;
 }
 //----------------------------
 public String getTableName(int i) {
   String name = "";
   switch (i) {
   case ParseVar.FRNAME:
     name = "frname";
   case ParseVar.LNAME:
     name = "lname";
   case ParseVar.AGE:
     name = "age";
   case ParseVar.CLUB:
     name = "club";
   case ParseVar.TIME:
     name = "time";
   }
   return name;
 }
 //----------------------------

} class ParseObject {

 public static final int VERB = 1000, VAR = 1010, MULTVAR = 1020;
 protected int value;
 protected int type;
 public int getValue() {
   return value;
 }
 public int getType() {
   return type;
 }

} class ParseVar extends ParseObject {

 static final int FRNAME = 0, LNAME = 1, AGE = 2, CLUB = 3, TIME = 4,
     tabMAX = 5;
 public ParseVar(String s) {
   s = s.toLowerCase();
   value = -1;
   type = VAR;
   if (s.equals("frname"))
     value = FRNAME;
   if (s.equals("lname"))
     value = LNAME;
   if (s.equals("age"))
     value = AGE;
   if (s.equals("club"))
     value = CLUB;
   if (s.equals("time"))
     value = TIME;
 }
 //--------------------------------------
 public boolean isLegal() {
   return (value >= 0);
 }

} class Kid {

 String frname, lname, club;
 int age;
 float time;
 //-------------------------------------
 public Kid(String line) {
   StringTokenizer tok = new StringTokenizer(line);
   String lnum = tok.nextToken();
   frname = tok.nextToken();
   lname = tok.nextToken();
   age = new Integer(tok.nextToken()).intValue();
   club = tok.nextToken();
   time = new Float(tok.nextToken()).floatValue();
 }
 //-------------------------------
 public Object getData(int key) {
   switch (key) {
   case ParseVar.FRNAME:
     return frname;
   case ParseVar.LNAME:
     return lname;
   case ParseVar.CLUB:
     return club;
   case ParseVar.AGE:
     return new Integer(age);
   case ParseVar.TIME:
     return new Float(time);
   }
   return null;
 }
 //--------------------------------
 public int getAge() {
   return age;
 }
 public float getTime() {
   return time;
 }
 public String getFrname() {
   return frname;
 }
 public String getLname() {
   return lname;
 }
 public String getClub() {
   return club;
 }

} class InputFile {

 RandomAccessFile f = null;
 boolean errflag;
 String s = null;
 public InputFile(String fname) {
   errflag = false;
   try {
     //open file
     f = new RandomAccessFile(fname, "r");
   } catch (IOException e) {
     //print error if not found
     System.out.println("no file found");
     errflag = true; //and set flag
   }
 }
 //-----------------------------------------
 public boolean checkErr() {
   return errflag;
 }
 //-----------------------------------------
 public String read() {
   //read a single field up to a comma or end of line
   String ret = "";
   if (s == null) //if no data in string
   {
     s = readLine(); //read next line
   }
   if (s != null) //if there is data
   {
     s.trim(); //trim off blanks
     int i = s.indexOf(","); //find next comma
     if (i <= 0) {
       ret = s.trim(); //if no commas go to end of line
       s = null; //and null out stored string
     } else {
       ret = s.substring(0, i).trim(); //return left of comma
       s = s.substring(i + 1); //save right of comma
     }
   } else
     ret = null;
   return ret; //return string
 }
 //-----------------------------------------
 public String readLine() {
   //read in a line from the file
   s = null;
   try {
     s = f.readLine(); //could throw error
   } catch (IOException e) {
     errflag = true;
     System.out.println("File read error");
   }
   return s;
 }
 //-----------------------------------------
 public void close() {
   try {
     f.close(); //close file
   } catch (IOException e) {
     System.out.println("File close error");
     errflag = true;
   }
 }
 //-----------------------------------------

} class kidClub implements Enumeration {

 String clubMask; //name of club
 Kid kid; //next kid to return
 Enumeration ke; //gets all kids
 KidData kdata; //class containing kids
 //----------------------------------------
 public kidClub(KidData kd, String club) {
   clubMask = club; //save the club
   kdata = kd; //copy the class
   kid = null; //default
   ke = kdata.elements(); //get Enumerator
 }
 //----------------------------------------
 public boolean hasMoreElements() {
   //return true if there are any more kids
   //belonging to the specified club
   boolean found = false;
   while (ke.hasMoreElements() && !found) {
     kid = (Kid) ke.nextElement();
     found = kid.getClub().equals(clubMask);
   }
   if (!found)
     kid = null; //set to null if none left
   return found;
 }
 //----------------------------------------
 public Object nextElement() {
   if (kid != null)
     return kid;
   else
     //throw exception if access past end
     throw new NoSuchElementException();
 }

} //50free.txt /* 1 Amanda McCarthy 12 WCA 29.28 2 Jamie Falco 12 HNHS 29.80 3 Meaghan O"Donnell 12 EDST 30.00 4 Greer Gibbs 12 CDEV 30.04 5 Rhiannon Jeffrey 11 WYW 30.04 6 Sophie Connolly 12 WAC 30.05 7 Dana Helyer 12 ARAC 30.18 8 Lindsay Marotto 12 OAK 30.23 9 Sarah Treichel 12 WYW 30.35 10 Ashley McEntee 12 RAC 30.47 11 Rachel Brookman 12 CAT 30.51 12 Michelle Ducharme 12 LEHY 30.51 13 Karleen Danais 12 NES 30.70 14 Megan Loock 12 WAC 30.90 15 Kaitlyn Ament 12 HNHS 30.93 16 Tara Schoen 12 WYW 31.01 17 Kate Olshefski 12 NCY 31.01 18 Emma Zuidema 12 HMST 31.07 19 Katie Persing 12 OAK 31.14 20 Christina Monsees 11 RAC 31.27 21 Kimberly Watcke 12 CDEV 31.50 22 Colleen Smith 12 AJSC 31.52 23 Chloe Osborne 12 GYWD 31.74 24 Natalia Fugate 12 WAC 31.75 25 Lisa McHale 11 RAC 31.76 26 Lindsay Cowles 11 NES 31.79 27 Jacquelyn Yavarone 12 HNHS 31.83 28 Molly Fenn 12 WRAT 31.84 29 Karin Brudvig 12 HMST 31.84 30 Annie Duffy 12 MGAT 31.90 31 Nicole Coia 11 WCA 31.94 32 Elizabeth Rice 12 WYW 31.96 33 Yvette Landwehr 12 WRAT 32.00 34 Ashley Recklet 12 SHEL 32.24 35 Lauren McKenna 11 PSDY 32.27 36 Kristen Fontaine 12 EDST 32.28 37 Diana Cooke 12 ZEUS 32.33 38 Kimberly Gambino 11 NES 32.43 39 Jenny Morgan 11 NES 32.49 40 Colleen Coelho 12 CDEV 32.50 41 Leigh Gordon 12 CDEV 32.62 42 Caitlin Gillen 12 WYW 32.75 43 Kristen Skroski 12 HNHS 32.91 44 Sarah Greenberg 11 CDEV 32.97 45 Kathy Collins 12 EHBB 33.11 46 Morgan Bullock 12 ICSC 33.33 47 Brittany Medlin 12 CAT 33.33 48 Haley Ottenbreit 12 HNHS 33.35 49 Laura Kunces 11 WAC 33.64 50 Hayley Wolfgruber 12 WYW 33.73 51 Katie Duffy 12 MGAT 34.24

• /

      </source>