More Sophisticated Behaviour 2 Using library classes to implement more advanced functionality. Also...

More Sophisticated Behaviour 2

Using library classes to implement Using library classes to implement more advanced functionality.more advanced functionality.

Also … class (Also … class (staticstatic) fields.) fields.

class Notebook {

private ArrayList<String> notes;

public Notebook () { ArrayList<String> notes = new ArrayList<String> (); }

public void addNote (String note) { notes.add (note); }

}

What’s Wrong with This?

class Notebook {




}

What’s Wrong with This?class Notebook {




}

Delete !!!Delete !!!

Keep going to the classes!

Objects First with Java - A Practical Introduction using BlueJ, © David J. Barnes, Michael Kölling

Main Concepts to be Covered

• More library classesMore library classes– sets and maps (sets and maps (HashSetHashSet and and HashMapHashMap) )

• Information hidingInformation hiding– publicpublic versus versus privateprivate

• Class fieldsClass fields– staticstatic and and finalfinal

• Writing documentationWriting documentation


ArrayListArrayList<String> <String> myListmyList = new = new ArrayListArrayList<String> ();<String> ();

myListmyList.add ("one"); .add ("one"); myListmyList.add ("two"); .add ("two"); myListmyList.add ("one");.add ("one");

Iterator<String> it = Iterator<String> it = myListmyList.iterator ();.iterator ();while (it.hasNext ()) {while (it.hasNext ()) { String s = it.next (); String s = it.next (); ... do something with s... do something with s}}

Using listslists

import java.util.import java.util.ArrayListArrayList;;import java.util.Iterator;import java.util.Iterator;

Seen Seen beforebefore


Using setssets

import java.util.import java.util.HashSetHashSet;;import java.util.Iterator;import java.util.Iterator;

HashSetHashSet<String> <String> mySetmySet = new = new HashSetHashSet<String> ();<String> ();

mySetmySet.add ("one"); .add ("one"); mySetmySet.add ("two"); .add ("two"); mySetmySet.add ("one");.add ("one");

Iterator<String> it = Iterator<String> it = mySetmySet.iterator ();.iterator ();while (it.hasNext ()) {while (it.hasNext ()) { String s = it.next (); String s = it.next (); ... do something with s... do something with s}}

NewNew


Using sets sets and listslists

All varieties of All varieties of setset and and listlist are examples of are examples of collectioncollection classes. We can use classes. We can use for-eachfor-each loops and loops and IteratorsIterators on on them. Of course, we can also use them. Of course, we can also use get (index)get (index) methods methods on them as well (or instead).on them as well (or instead).

One difference is that a One difference is that a setset one holds one holds one instance one instance of of objects that are objects that are equalequal – i.e. if – i.e. if aa and and bb have both been have both been added to a added to a setset and and a.equals(b)a.equals(b), then only one of , then only one of them will be there. It is not guaranteed which one is them will be there. It is not guaranteed which one is kept. So, never search a kept. So, never search a setset using using ====..




A second difference is that A second difference is that the orderthe order in which elements in which elements are kept in a are kept in a setset is not defined. For example, the order is not defined. For example, the order of elements returned by a of elements returned by a for-eachfor-each loop or loop or Iterator Iterator is is not necessarilynot necessarily the same order in which they were the same order in which they were added. added.

All varieties of All varieties of setset and and listlist are examples of are examples of collectioncollection classes. We can use classes. We can use for-eachfor-each loops and loops and IteratorsIterators on on them. Of course, we can also use them. Of course, we can also use get (index)get (index) methods methods on them as well (or instead).on them as well (or instead).




Go look them up in the Java API documentation !!!



‘Eliza’ ProjectSeen Seen

beforebefore

InputReaderInputReader ResponderResponder

SupportSystemSupportSystem

See Chapter05, tech-support projectsSee Chapter05, tech-support projectsSee Chapter05, tech-support projectsSee Chapter05, tech-support projects


‘Eliza’ Main Loopboolean finished = false;boolean finished = false;

while while (!finished(!finished) {) {

String input = reader.getInput ();

if (if (input.startsWith ("bye")) {) { finished = true;finished = true; } } else { else { String response = responder.generateResponse (); System.out.println (response); } }

}}Chapter05, tech-support1, Chapter05, tech-support1, SupportSystem.start()SupportSystem.start()Chapter05, tech-support1, Chapter05, tech-support1, SupportSystem.start()SupportSystem.start()


This returns the lineThis returns the lineof text typed by the of text typed by the

customer.customer.


Go look this up Go look this up ((java.util.HashSetjava.util.HashSet))

boolean finished = false;boolean finished = false;


HashSet<String> input = reader.getInput ();

if (if (input.contains ("bye")) {) { finished = true;finished = true; } } else { else { String response = responder.generateResponse (input); System.out.println (response); } }

}}

‘Eliza’ Main Loop

Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()

NewNew

This returns the set of This returns the set of different words typed by different words typed by

the customer.the customer.

Now, “bye” can be any Now, “bye” can be any word – not just the first.word – not just the first.






}}Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()

NewNew

This is the first time the This is the first time the response is dependant response is dependant

upon the enquiry!upon the enquiry!


Note: in the project code, Note: in the project code, scannerscanner is (confusingly) called is (confusingly) called reader reader ……Note: in the project code, Note: in the project code, scannerscanner is (confusingly) called is (confusingly) called reader reader ……

This is aThis is a StringString

‘Eliza’ InputReaderpublic String getInput ()public String getInput (){{

System.out.print ("> "); System.out.print ("> "); String inputLine = String inputLine = scanner.nextLine(); scanner.nextLine();

return inputLine;return inputLine; }}

Chapter05, tech-support1, Chapter05, tech-support1, InputReader.getInput()InputReader.getInput()Chapter05, tech-support1, Chapter05, tech-support1, InputReader.getInput()InputReader.getInput()

NewNew

private Scanner scanner;private Scanner scanner;private Scanner scanner;private Scanner scanner;

import java.util.Scanner;import java.util.Scanner;import java.util.Scanner;import java.util.Scanner;

go look this up go look this up ((java.util.Scannerjava.util.Scanner))


Note: in the project code, Note: in the project code, scannerscanner is (confusingly) called is (confusingly) called reader reader ……Note: in the project code, Note: in the project code, scannerscanner is (confusingly) called is (confusingly) called reader reader ……

‘Eliza’ InputReaderpublic HashSet<String> getInput ()public HashSet<String> getInput (){{

System.out.print ("> ") ; System.out.print ("> ") ; String inputLine = String inputLine = scanner.nextLine().trim().toLowerCase(); scanner.nextLine().trim().toLowerCase();

... more stuff... more stuff }}

Chapter05, tech-support-complete, Chapter05, tech-support-complete, InputReader.getInput()InputReader.getInput()Chapter05, tech-support-complete, Chapter05, tech-support-complete, InputReader.getInput()InputReader.getInput()

NewNew






... more stuff ... more stuff }}

NewNew


This is aThis is a StringString







NewNew


So is this …So is this …









NewNew

go look these up go look these up ((java.lang.Stringjava.lang.String))


So is this …So is this …go look this up go look this up

((java.util.Scannerjava.util.Scanner))


go look this up go look this up ((java.lang.Stringjava.lang.String))

public HashSet<String> getInput ()public HashSet<String> getInput (){{

System.out.print ("> "); System.out.print ("> "); String inputLine = String inputLine = scanner.nextLine().trim().toLowerCase(); scanner.nextLine().trim().toLowerCase();

String[] wordArray = inputLine.split (" ");String[] wordArray = inputLine.split (" ");

HashSet<String> wordSet = new HashSet<String> ();HashSet<String> wordSet = new HashSet<String> (); for (String word : wordArray) { for (String word : wordArray) { wordSet.add (word); wordSet.add (word); } }

return wordSet; return wordSet;

}}

‘Eliza’ InputReaderNewNew

which eliminates repeated words


converts the converts the array to a setarray to a set



Maps

• Maps are Maps are collectionscollections that contain that contain pairs of valuespairs of values..

• A pair consists of a A pair consists of a keykey and a and a valuevalue..

• Lookup works by supplying a key, Lookup works by supplying a key, and retrieving the corresponding and retrieving the corresponding value.value.

• An example: An example: a telephone booka telephone book..


Using Maps

• A map with A map with StringStringss both as both as keyskeys and and valuesvalues::

phoneBook:HashMap

"Rick Blaine" "(531) 9392 4587"

"Ilsa Lund" "(402) 4536 4674"

"Victor Laszlo" "(998) 5488 0123"


HashMapHashMap<String, String> <String, String> phoneBookphoneBook = = new new HashMapHashMap<String, String> ();<String, String> ();

Using Maps

phoneBookphoneBook.put ( "Rick Blaine", "(531) 9392 4587");.put ( "Rick Blaine", "(531) 9392 4587");phoneBookphoneBook.put ( "Ilsa Lund", "(402) 4536 4674");.put ( "Ilsa Lund", "(402) 4536 4674");phoneBookphoneBook.put ("Victor Laszlo", "(998) 5488 0123");.put ("Victor Laszlo", "(998) 5488 0123");

String phoneNumber = String phoneNumber = phoneBookphoneBook.get ("Rick Blaine");.get ("Rick Blaine");......System.out.println (phoneNumber);System.out.println (phoneNumber);

valuevaluekeykey

keykeyvaluevalue



Using Maps


String phoneNumber = String phoneNumber = phoneBookphoneBook.get ("Ricky Blaine");.get ("Ricky Blaine");......

valuevaluekeykey

Important:Important: invoking invoking getget with a with a keykey that does not exist that does not exist in the in the HashMapHashMap object returns object returns nullnull. This can be useful!. This can be useful!

keykeyvaluevalue



Using Maps


String phoneNumber = String phoneNumber = phoneBookphoneBook.get ("Ricky Blaine");.get ("Ricky Blaine");if (phoneNumber == null) {...}if (phoneNumber == null) {...}else {...}else {...}

valuevaluekeykey

Important:Important: invoking invoking getget with a with a keykey that does not exist that does not exist in the in the HashMapHashMap object returns object returns nullnull. This can be useful!. This can be useful!

keykeyvaluevalue



Using Maps


String phoneNumber = String phoneNumber = phoneBookphoneBook.get ("Ricky Blaine");.get ("Ricky Blaine");if (phoneNumber == null) {...}if (phoneNumber == null) {...}else {...}else {...}

valuevaluekeykey

"Ricky Blaine""Ricky Blaine" was not in the was not in the phoneBookphoneBook … …

"Ricky Blaine""Ricky Blaine" was in the was in the phoneBookphoneBook … …

keykeyvaluevalue



beforebefore





go look this up go look this up ((java.lang.Stringjava.lang.String))

public HashSet<String> getInput ()public HashSet<String> getInput (){{

System.out.print ("> "); System.out.print ("> "); String inputLine = String inputLine = scanner.nextLine().trim().toLowerCase(); scanner.nextLine().trim().toLowerCase();

String[] wordArray = inputLine.split (" ");String[] wordArray = inputLine.split (" ");

HashSet<String> wordSet = new HashSet<String> (); HashSet<String> wordSet = new HashSet<String> (); for (String word : wordArray) { for (String word : wordArray) { wordSet.add (word); wordSet.add (word); } }

return wordSet; return wordSet;

}}

‘Eliza’ InputReaderJust Just seenseen



convert the convert the array to a setarray to a set




beforebefore









}}Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()Chapter05, tech-support-complete, Chapter05, tech-support-complete, SupportSystem.start()SupportSystem.start()

Just Just seenseen

This is the first time the This is the first time the response is dependant response is dependant

upon the enquiry!upon the enquiry!



beforebefore





Generating Random Responses

public Responder ()public Responder (){{ randomGenerator = new Random ();randomGenerator = new Random (); responses = new ArrayList<String> ();responses = new ArrayList<String> (); fillResponses ();fillResponses ();}}

private void fillResponses ()private void fillResponses (){{ ......}}

public String generateResponse ()public String generateResponse (){{ int index =int index = randomGenerator.nextInt (responses.size ()); randomGenerator.nextInt (responses.size ()); return responses.get (index); return responses.get (index);}}

Chapter05, tech-support2, Chapter05, tech-support2, ResponderResponderChapter05, tech-support2, Chapter05, tech-support2, ResponderResponder

returns a random returns a random number in the legal number in the legal range for indexing range for indexing responsesresponses



Generating Better Responses

public Responder ()public Responder (){{ randomGenerator = new Random ();randomGenerator = new Random (); defaultResponses = new ArrayList<String> (); defaultResponses = new ArrayList<String> (); fillDefaultResponses (); fillDefaultResponses (); responseMap = new HashMap<String, String> ();responseMap = new HashMap<String, String> (); fillResponseMap ();fillResponseMap ();}}

... private void fillDefaultResponses ()... private void fillDefaultResponses ()

... private void fillResponseMap ()... private void fillResponseMap ()

private String pickDefaultResponse ()private String pickDefaultResponse (){{ int index =int index = randomGenerator.nextInt (defaultResponses.size randomGenerator.nextInt (defaultResponses.size ());()); return responses.get (index); return responses.get (index);}}

Chapter05, tech-support-complete, Chapter05, tech-support-complete, ResponderResponder


NewNew

Same as Same as tech-support2tech-support2 generateResponsegenerateResponse




private void fillDefaultResponses ()private void fillDefaultResponses (){{ defaultResponses.add ("That sounds odd. Tell me more?");defaultResponses.add ("That sounds odd. Tell me more?"); defaultResponses.add ("No one else complained!"); defaultResponses.add ("No one else complained!"); defaultResponses.add ("Interesting. Tell me more?");defaultResponses.add ("Interesting. Tell me more?"); defaultResponses.add ("Do you have a dll conflict?");defaultResponses.add ("Do you have a dll conflict?"); defaultResponses.add ("Read the ******* manual!");defaultResponses.add ("Read the ******* manual!"); defaultResponses.add ("That's not a bug - it's a feature!");defaultResponses.add ("That's not a bug - it's a feature!"); ... etc.... etc.}}

Generating Random Responses

Same as Same as tech-support2tech-support2 fillResponsesfillResponses



public Responder ()public Responder (){{ randomGenerator = new Random ();randomGenerator = new Random (); defaultResponses = new ArrayList<String> (); defaultResponses = new ArrayList<String> (); fillDefaultResponses (); fillDefaultResponses (); responseMap = new HashMap<String, String> ();responseMap = new HashMap<String, String> (); fillResponseMap ();fillResponseMap ();}}

private String pickDefaultResponse ()private String pickDefaultResponse (){{ int index =int index = randomGenerator.nextInt (defaultResponses.size randomGenerator.nextInt (defaultResponses.size ());()); return responses.get (index); return responses.get (index);}}



Same as Same as tech-support2tech-support2 generateResponsegenerateResponse

Just Just seenseen

... private void fillDefaultResponses ()... private void fillDefaultResponses ()

... private void fillResponseMap ()... private void fillResponseMap ()


Generating Relevant Responses

private void fillResponseMap ()private void fillResponseMap (){{ responseMap.put ("crash",responseMap.put ("crash", "Well,"Well, it never crashes here!\n" + "Tell me about your configuration?"); responseMap.put ("slow",responseMap.put ("slow", ""Upgrade your processor then!\n" + "That should solve your problems."); responseMap.put ("windows",responseMap.put ("windows", "This is a known bug"This is a known bug in Windows!\n” + "Please report it to Microsoft"); ... etc.}}



NewNew


public String generateResponse (public String generateResponse (HashSet<String> words)){{ Iterator<String> it = Iterator<String> it = wordswords.iterator ();.iterator (); while (it.hasNext ()() { while (it.hasNext ()() { String String wordword = it.next (); = it.next (); String String responseresponse = = responseMap.get (word)responseMap.get (word);; if ( if (responseresponse != null) { != null) { return return responseresponse;; } } } } return return pickDefaultResponse ();pickDefaultResponse ();}}




NewNew

supply the supply the keykey

If the If the keykey is in the is in the MapMap, this returns the , this returns the matching matching valuevalue – otherwise returns – otherwise returns nullnull..






Or …Or …

public String generateResponse (public String generateResponse (HashSet<String> words)){{ for (String for (String wordword : : wordswords) {) { String String responseresponse = = responseMap.get (word)responseMap.get (word);; if ( if (responseresponse != null) { != null) { return return responseresponse;; } } } } return return pickDefaultResponse ();pickDefaultResponse ();}}

supply the supply the keykey




Revision

Make sure you Make sure you understand understand every every statementstatement on the on the

next slide …next slide …


Revision• A A classclass is a template from which is a template from which objectsobjects can be can be

constructed.constructed.

• A A classclass defines the defines the data fieldsdata fields held by its objects, together held by its objects, together with logic for with logic for constructorsconstructors of its objects and of its objects and methodsmethods for for accessing and operating on their data. accessing and operating on their data.

• Methods (and constructors) may declare and use their own Methods (and constructors) may declare and use their own local variableslocal variables – these exist only for the duration of their – these exist only for the duration of their method (or constructor). On the other hand, method (or constructor). On the other hand, data fieldsdata fields last last for the duration of their object.for the duration of their object.

• Methods and constructors may be passed Methods and constructors may be passed parametersparameters – – these exist only for the duration of the method or these exist only for the duration of the method or constructor.constructor.

• Data fields, parameters and local variables may have Data fields, parameters and local variables may have classclass types (i.e. they are references to other objects) or types (i.e. they are references to other objects) or primitiveprimitive types (e.g. types (e.g. intint, , floatfloat, , booleanboolean, , charchar, …)., …).

• Data fields, constructors and methods may be declared Data fields, constructors and methods may be declared publicpublic or or privateprivate..


Revision

If you don’t,If you don’t,you must find outyou must find out … … e.g. read thee.g. read the

book!book!


• PublicPublic attributes attributes (fields, constructors, (fields, constructors, methods)methods) are accessible to other are accessible to other classes.classes.

• Fields should not (usually) be public.Fields should not (usually) be public.

• PrivatePrivate attributes are accessible only attributes are accessible only within the same class.within the same class.

• Only methods and constructors that Only methods and constructors that are intended for use by other classes are intended for use by other classes should be should be publicpublic..

Information hiding


Information hiding• Data belonging to one object Data belonging to one object should should

be hiddenbe hidden from other objects. from other objects.

• Know Know whatwhat an object can do, not an object can do, not howhow it does it.it does it.

• Information hiding increases the level Information hiding increases the level of of independenceindependence..

• Independence of modules Independence of modules ((“low “low coupling”)coupling”) is important for building is important for building and maintaining large systems.and maintaining large systems.


Class Fields

NewNew

Chapter05, ballsChapter05, ballsChapter05, ballsChapter05, balls


• A A classclass defines the defines the data fieldsdata fields held by its objects, held by its objects, together with logic for together with logic for constructorsconstructors of its objects and of its objects and methodsmethods for accessing and operating on their data. for accessing and operating on their data.

• A A classclass may also define may also define class fieldsclass fields, which are shared , which are shared by all its objects.by all its objects.

• The class itself holds a single instance of each of these The class itself holds a single instance of each of these fields fields – its objects all work with the same instances– its objects all work with the same instances..

• Compare this with Compare this with data fieldsdata fields – objects all work with – objects all work with their own (different) instancestheir own (different) instances. .

• Class fieldsClass fields are declared with the keyword: are declared with the keyword: staticstatic..

• In the In the BouncingBallBouncingBall class, class, gravitygravity is a is a class fieldclass field whose common value is shared by all its instances – whose common value is shared by all its instances – the the data fieldsdata fields xPositionxPosition and and yPositionyPosition have values have values that are specific for each ball.that are specific for each ball.

Class Fields


A Class Constant

privateprivate staticstatic finalfinal int gravity = 3; int gravity = 3;

private private : : specifies thespecifies the visibiltyvisibilty of the declaration. of the declaration.

static static :: specifies that all specifies that all objectsobjects of this class of this class share this field – it belongs to the share this field – it belongs to the classclass..

finalfinal :: specifies that the value given cannot bespecifies that the value given cannot be changed – it is a changed – it is a constantconstant..

Note:Note: finalfinal can be applied to can be applied to anyany field (class or field (class or data), method local variable or parameter.data), method local variable or parameter.


Writing class documentation

• Your own classesYour own classes should be documented in should be documented in the same way and to the same standard as the same way and to the same standard as the the built-in library classesbuilt-in library classes..

• Other people should be able to use your Other people should be able to use your classes without reading their classes without reading their implementation.implementation.

• Make your class a library class …Make your class a library class …

• Java libraries are called Java libraries are called packagespackages … …

Investigate !!!

Investigate !!!

Investigate !!!

Investigate !!!


Elements of documentation

• Documentation for a class should include:– the class name– a description of the overall purpose and

characteristics of the class– a version number– author names– documentation explaining each

constructor and each method


Elements of documentation

• Documentation for each constructor and method should include:– the name of the method– the return type (if any)– the parameter names and types– a description of the purpose and function

of each method– a description of each parameter– a description of the value returned (if

any)


/**/** * The Responder class represents a response * The Responder class represents a response * generator object. It is used to generate * generator object. It is used to generate * an automatic response. * an automatic response. * * * @author Michael Kölling and David J. Barnes * @author Michael Kölling and David J. Barnes * @version 1.0 (30.Mar.2006) * @version 1.0 (30.Mar.2006) */ */class Responderclass Responder{{ ... ...}}

javadoc - Class comments


/**/** * Change the colour of this shape. The new colour * Change the colour of this shape. The new colour * becomes visible immediately. Legal colour strings * becomes visible immediately. Legal colour strings * are "White", "Orange", "Blonde", "Pink", "Blue" * are "White", "Orange", "Blonde", "Pink", "Blue" * and "Brown". * and "Brown". * * * @param colour The name of the new colour. * @param colour The name of the new colour. * @return true, if the colour was successfully * @return true, if the colour was successfully changed; changed; * false, if the colour name is invalid. * false, if the colour name is invalid. */ */public boolean changeColour (String colour) public boolean changeColour (String colour) {{ ... ...}}

javadoc - Method comments


Review• Java has an extensive class library Java has an extensive class library

(packages)(packages)..

• A good programmer must know how to find A good programmer must know how to find things in the library and become familiar things in the library and become familiar with those regularly used.with those regularly used.

• The documentation tells us what we need to The documentation tells us what we need to know to use a class know to use a class (interface)(interface)..

• The implementation is hidden The implementation is hidden (information (information hiding)hiding)..

• We document our classes so that the We document our classes so that the interface can be read on its own interface can be read on its own (class (class comment, method comments)comment, method comments)..

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