ITI 1221. Introduction to Computing II Lab-7 Dewan Tanvir Ahmed University of Ottawa

ITI 1221. Introduction to Computing IILab-7

Dewan Tanvir AhmedUniversity of Ottawa

Today’s Objective

Understanding the current Assignment, e.g. Assignment 3 Reviewing the solution of Assignment 2 Reviewing the solution of Mid term GUI and Event Driven Programming

Assignment 3

Objectiveso Further understanding of exception handling in Javao Learn about two implementations of Queues o Introduction to Queue-based algorithms

Breath-First Search (BFS) algorithm

Assignment 3 (cont..)

Exceptions o Create a new exception type called EmptyQueueException

A subclass of RuntimeException The class EmptyQueueException has two constructors

– A default constructor with no parameters– A constructor with a parameter of type String,

» which is used to save a reference to an error message for later retrieval by the getMessage method


Exceptions o Create a new exception type called QueueOverflowException

A subclass of RuntimeException The class QueueOverflowException has two constructors

– A default constructor with no parameters– A constructor with a parameter of type String, which is used to save a reference to

an error message for later retrieval by the getMessage method


Exceptions o modify the methods of the classes LinkedQueue and CircularQueue

To validate the pre-conditions and throw the appropriate exception when needed:

– EmptyQueueException, – QueueOverflowException and – IllegalArgumentException


Copy o The method copy() creates a duplicate of a queue containing the

same elements and be in the same order

o It creates a copy of a queue such that the values of the queue and its copy are shared, Shallow copy.

o Class LinkedQueue: public LinkedQueue copy() Adding elements to a linked structure having a front reference and rear

reference You can’t use the instance methods of this class to implement this method NB. Two queues are sharing the values but not the nodes

o Class public CircularQueue copy() Exercise of wrapping front and rear around the boundaries You can’t use the instance methods of this class to implement this method The elements of the duplicate should be stored at positions 0 to size - 1


public boolean equals( Object other )Override the method

public boolean equals( Object other ) It returns

– true if other designates a Queue (any implementation of the interface Queue) that contains the same number of elements as this queue, and each element of the other queue must be “equals” to the corresponding element in this queue

– false otherwise

Both queues must not be changed by the method equals, i.e. before and after a call to the method equals, this and the other queue must contain the same elements, in the same order


Test o Write a Test program for the methods copy and equals of the classes

LinkedQueue and CircularQueue.


Questions??? (LinkedQueue, CircularQueue) Size Wrapping Enqueue Dequeue Empty! Full!

Assignment 3, Part II

Queue Based Algorithmso BFS

Assignment 3, Part II (cont..)

Class HTMLo HTML document = new HTML( "http://www.site.uottawa.ca/~turcotte/a3/" );

int count=0;

while ( document.hasMoreUrls() ) { String url = document.nextUrl(); count++; }

System.out.println( "This document has " + count + " links." );

o How to get the content document.getPage();


Class Solutiono A Solution has two instance variables (both of type String).

One that designates the path represented by the solution. The other stores the last URL of the path represented by the solution;

o Constructors The constructor Solution( String lastUrl )

– sets both instance variables to lastUrl.

The constructor Solution( Solution partial, String lastUrl ) – sets the path of this Solution to that of partial concatenated with lastUrl; – path = partial.getpath() -> lastUrl

It also sets the instance variable for the last URL of this object to lastUrl;

o A solution has two access methods, getPath and getLasUrl


Crawlero The class Crawler contains three static methods that are used to find a

path from a Web page A to a Web page Bo private static boolean isValid( String url )

returns true – if url is a well formed URL designating an existing/readable Web page, and false

otherwise. Use the fact that the constructor of an HTML object

Throws an exception, of type MalformedURLException, – if the url is not well formed

Throws an exception, of type IOException, – if the content of the page cannot be successfully read

o Any Question?


Crawler o private static Solution solve( String a, String b )

Implement a breath-first search algorithm for finding a path from a Web page A to a Web page B.

The breath-first search uses a Queue data structure (this can be your own implementation of LinkedQueue)

The algorithm initializes the queue to contain just the partial solution that consists of the Web page A only, and repeatedly does the following:

– dequeues a partial solution off the queue; – extend the partial solution by one URL in all possible ways– enqueues each of the “valid” extension


Crawler o public static void main( String[] args )

The main method prints the following message unless there are exactly two arguments on the command line, and exists immediately

– Usage: java Crawler src dst

If the command line has two arguments, those arguments are used for calling the method solve

The main method prints the path if it exists, and “no path” if no such path was found

Solution – Assignment 2

Let’s Goo Click here

Mid-Term Solution - Q1

Part Ao Implement the three classes, as well as the interface Player.

Make sure to include the constructors For each attribute

– write the access methods– The values of the attributes must be valid

» If the value of the parameter is less than 0.0 then set the value of the attribute to 0.0

» Similarly, if the value of the parameter is larger than the upper limit then set the attribute to its upper limit

Finally, implement the methods attack

Mid-Term Solution Q1 (cont..)

Implementation of interface Player:o All players of the game have a method double attack() that returns a

value representing the strength of the attack. o Player is an interface declaring the method double attack()

public interface Player {public abstract double attack();

}


Implementation of abstract class AbstractPlayer:o An AbstractPlayer defines the characteristics that are common to all

the creatureso This abstract class implements the interface Playero All the creatures have

A name (a character String) A life meter (a double ranging from 0.0 to 100.0)

– The initial value of the life meter is 50.0

o Implement constructor methodo Implement access methods

getters and setter methods for attributes name and life meter


public abstract class AbstractPlayer implements Player {private static final double LIFE_METER_INIT = 50.0;private static final double LIFE_METER_MAX = 100.0;private static final double LIFE_METER_MIN = 0.0;private String name;private double lifeMeter;public AbstractPlayer( String name ) {

lifeMeter = LIFE_METER_INIT;this.name = name;

}public String getName() {

return name;}public String setName( String name ) {

this.name = name;}

public double getLifeMeter() {return lifeMeter;

}


public void setLifeMeter( double value ) {lifeMeter = value;if ( lifeMeter < LIFE_METER_MIN ) {

lifeMeter = LIFE_METER_MIN;} else if ( lifeMeter > LIFE_METER_MAX ) {

lifeMeter = LIFE_METER_MAX;}

}}


Class Uldrao An Uldra is a creature (player) that carries a bottle filled with poison

(a double value in the range 0.0 . . . 100.0)o Uldra creatures have a tendency to misplace their bottles (a boolean

value indicates if this Uldra has or not its bottle)o The strength of an attack is zero if the Uldra has no bottle.

Otherwise, the strength of an attack is 10.0, or the remaining amount of poison (which ever value is smaller)

o The strength of the attack reduces the quantity of poison left by the same amount


public class Uldra extends AbstractPlayer {private boolean hasABottle;private double poison;public Uldra( String name ) {

super( name );hasABottle = false;poison = 0.0;

}public boolean hasABottle() { return hasABottle; }public void setHasBottle( boolean value ) {

hasABottle = value;if ( ! hasABottle ) {

poison = 0.0;}

}public double getPoison() { return poison; }


public void setPoison( double value ) {if ( hasABottle ) {

poison = value;if ( poison < 0.0 ) {

poison = 0.0;} else if ( poison > 100.0 ) {

poison = 100.0;}

}}public double attack() {

double result = 10.0;if ( ! hasABottle ) {

result = 0;} else if ( getPoison() < result ) {

result = getPoison();}setPoison( getPoison() - result );return result;

}}


Class Yakkuo Yakku creatures have magical powers (double, range 0.0 . . .

100.0, the initial value is 10.0)o The strength of the attack depends on both its life meter and its

magical powers. Specifically, a weight w is calculated as being the value of the life meter divided by 10.0

o The weight w is then multiplied by the level of magical powers to obtain the strength of the attack

o An attack reduces both the life meter and the magical powers by the strength of the attack.


public class Yakku extends AbstractPlayer {private static final double MAGIC_POWERS_MAX = 100.0;private static final double MAGIC_POWERS_MIN = 0.0;private static final double MAGIC_POWERS_INIT = 40.0;private double magicPowers = MAGIC_POWERS_INIT;public Yakku( String name ) {

super( name );}public double getMagicPowers() { return magicPowers; }

public void setMagicPowers( double value ) {magicPowers = value;if ( magicPowers < MAGIC_POWERS_MIN) {

magicPowers = MAGIC_POWERS_MIN;} else if ( magicPowers > MAGIC_POWERS_MAX ) {

magicPowers = MAGIC_POWERS_MAX;}

}


public double attack() {double w = getLifeMeter() / 10.0;double result = w * magicPowers;setLifeMeter( getLifeMeter() - result );magicPowers = magicPowers - result;return result;

}}


Part Bo Write a polymorphic class method, duel, that has two parameters,

both of type AbstractPlayer, first and second.o Rules

While both players are alive (i.e. their life meter is greater than zero) The first player launches an attack onto the second one If the second player is still alive, it launches an attack onto the first

player When a player “a” launches an attack onto a player “b”, you must

reduce the value of the life meter of “b” by a.attack() Finally, the method displays the name of the player that is still alive


public static void duel( AbstractPlayer first, AbstractPlayer second ) {

while ( first.getLifeMeter() > 0.0 && second.getLifeMeter() > 0.0 ) {

double strength;

strength = first.attack();

second.setLifeMeter( second.getLifeMeter() - strength );

if ( second.getLifeMeter() > 0.0 ) {

strength = second.attack();

first.setLifeMeter( first.getLifeMeter() - strength );

}

}

AbstractPlayer alive = first;

if ( second.getLifeMeter() > 0.0 ) {

alive = second;

}

System.out.println( alive.getName() + " is alive!" );

}


Calculator c = new Calculator();c.execute( "40 5 2 4 1 ~ print + print ^ print * print - print" );

-top-INTEGER: -1INTEGER: 4INTEGER: 2INTEGER: 5INTEGER: 40-bottom--top-INTEGER: 3INTEGER: 2INTEGER: 5INTEGER: 40-bottom-

-top-INTEGER: 8INTEGER: 5INTEGER: 40-bottom--top-INTEGER: 40INTEGER: 40-bottom--top-INTEGER: 0-bottom

Mid-Term Solution Q2

Correct at least 5 mistakes (logic, runtime or compile-time errors) in the partial implementation

"implements Stack" missing constructor

o declaration of a local variable elems masks the instance variable elem

o ’capacity = capacity’ should be o ’this.capacity = capacity’, otherwise, the instance variable

capacity will not be initializedo this.increment not assigned

increaseSizeo needs a for loop to copy the elements or System.arraycopy

Popo should decrease size then access the elemento "return saved" missingo (should be calling decreaseSize after removing the element. )


Complete the partial implementation of the class DynamicArrayStack

public void push( Object element ) {if (size == elems.length) {

increaseSize();}elems[ size ] = element;size = size + 1;

}



private void increaseSize() {Object[] newElems;newElems = new Object[elems.length + increment];

// Copying all the elements to the new arraynewElems = elems;

// Replacing elems with the new and larger arrayelems = newElems;

}



public Object pop() {size = size - 1;Object saved = elems[ size ];

// Scrubbing the memory!elems[ size ] = null;if (elems.length > capacity && ( elems.length - size ) >= increment) {

decreaseSize();}return saved;

}


private void decreaseSize() {int newSize = elems.length - increment;if ( newSize < capacity ) {

newSize = capacity;}Object[] newElems;newElems = new Object[ newSize ];for ( int i=0; i<size; i++ ) {

newElems[ i ] = elems[ i ];}

// Replacing elems with the new/smaller array elems = newElems;

}



In the class CombinationLock, override the method equals.o Two locks are equals if

Their status are “equals” and both CombinationLock have the same combination (defined by the variables first, second and third)

Otherwise, the method returns false

o No values are considered illegal; in particular, the method should be handling null values.


public boolean equals( Object obj ) {if ( obj == null || ! ( obj instanceof CombinationLock ) )

return false;CombinationLock other = (CombinationLock) obj;boolean result = true;if ( first != other.first )

result = false;else if ( second != other.second )

result = false;else if ( third != other.third )

result = false;else if ( status == null )

result = ( other.status == null );else

result = status.equals( other.status );return result;

}


LinkedPair - Part A Draw the memory diagram representing the content of the

memory after the execution of the following statementPair p = new LinkedPair ( new Name("Joseph", "Rotblat"), new Name("Wangari", "Maathai"));


LinkedPair - Part B For the partial implementation of the class LinkedPair, write the instance

method public sort() that sorts the (two) elements of a LinkedPair Rules

o Change the order of the elements (objects of the class Elem) o exchanging the values of the nodes is not acceptable.


public void sort() {if ( first.value.compareTo( first.next.value ) > 0 ) {

Elem newFirst = first.next;newFirst.next = first;first.next = null;first = newFirst;

}}

Part C Complete the implementation of the method String toString(). It returns a

String representation of the pairo starting with “(”o Followed by the String representation of the first object of the pairo Followed by “,”o Followed by the String representation of the second object of the pairo Followed by “)”.

public String toString() {return "(" + first.value + "," + first.next.value + ")";

}


Part Ao Define a new checked exception called ZendaIOException. o This should be a specialized IOException.

public class ZendaIOException extends IOException {public ZendaIOException() {

super();}public ZendaIOException( String message ) {

super( message );}

}



import java.io.FileInputStream;import java.io.FileNotFoundException;

public class Zenda {

private static void getConfig( String name ) throws ZendaIOException {if ( name == null ) {

throw new IllegalArgumentException( "null value" );}FileInputStream input;try {

input = new FileInputStream( name );} catch ( FileNotFoundException e ) {

throw new ZendaIOException( "file not found: " + name ); }}


private static void init() throws ZendaIOException{getConfig( "config.dat" );

}public static void main( String[] args ) {

try {init();

} catch ( ZendaIOException e ) {System.err.println( "ERROR READING CONFIG FILE" );e.printStackTrace();System.exit( 1 );

} }}

Part Co Explain why a runtime exception will occur if the following statements

are executed.

public class Manager {private Object[] elems;public Manager( int capacity ) {

if ( elems.length == 0 ) {elems = new Object[ capacity ];

}}public static void main( String[] args ) {

Manager m = new Manager( 100 );}

}

Mid-Term Solution (cont..)

NullPointerException?

GUI and Event Driven Programming

Any component can be the source of an evento A button generates an event when you click on it.

Any class can be a listener for an evento It simply implements the method (s) of the interface

The object that handles the event generated from the click of a button needs to implement the interface ActionListener.

The object that handles the event generated when a window is closed must implement the interface WindowListener.

GUI and Event Driven Programming (cont..)

The event generated by the source component is sent to the listeners who registered with the component.

The source has a method addActionListener who needs as a parameter an object that implements the interface ActionListener.

Since the handler implements the interface ActionListener, the source knows that the handler has a method actionPerformed(...).

Exampleo private DisplayArea display = new DisplayArea(); o button.addActionListener(display);

Source

Listener

Object

Registration


import java.awt.*; import java.awt.event.*;

public class GUI extends Frame {

private Button bLeft = new Button("Left"); private Button bRight = new Button("Right"); private DisplayArea display = new DisplayArea();

public GUI() { super("DGD - Week 8");setBackground(Color.WHITE); add(display, BorderLayout.CENTER);

Panel p = new Panel(); p.add(bLeft); p.add(bRight); add(p, BorderLayout.SOUTH);


bLeft.addActionListener(display); bRight.addActionListener(display); addWindowListener(new WindowAdapter() {

public void windowClosing(WindowEvent e) { System.exit(0); }

} ); pack(); show(); }

public static void main(String[] args) { new GUI();

}}


import java.awt.*; import java.awt.event.*;

class DisplayArea extends Canvas implements ActionListener { private Point center;

DisplayArea() { setSize(200,200); center = new Point(100,100);

}

public void paint(Graphics g) { g.setColor(Color.RED); g.fillOval(center.x - 5, center.y - 5, 10, 10);

}

public void actionPerformed(ActionEvent e) { String cmd = e.getActionCommand(); if (cmd.equals("Left")) {

center.x = (center.x + 190) % 200; // subtracts 10 }else if (cmd.equals("Right")) {

center.x = (center.x + 10) % 200; } repaint(); } }

WindowAdapter

A Frame has a method addWindowListener that allows you to register an object that implements the interface WindowListener.

The interface lists 7 methods: o public void windowOpened(WindowEvent e); o public void windowClosing(WindowEvent e); o public void windowClosed(WindowEvent e); o public void windowIconified(WindowEvent e); o public void windowDeiconified(WindowEvent e); o public void windowActivated(WindowEvent e); o public void windowDeactivated(WindowEvent e);

Still, in order to register a handler with the frame we have to provide an object that implements this interface,

o which means that we have to implement the 7 methods

Solution - WindowAdapter

Solution - 1: All the methods are empty except for windowClosing:

import java.awt.event.*; class MyWindowListener implements WindowListener {

public void windowOpened(WindowEvent e) {} public void windowClosed(WindowEvent e) {} public void windowClosing(WindowEvent e) {

System.exit(0); } public void windowIconified(WindowEvent e) {} public void windowDeiconified(WindowEvent e) {} public void windowActivated(WindowEvent e) {} public void windowDeactivated(WindowEvent e) {}

}

Solution - WindowAdapter

Solution -2 1. Inherit all the empty methods and 2. implements the ones we need for this application.

class MyWindowAdapter extends WindowAdapter { public void windowClosing(WindowEvent e) {

System.exit(0); }

}

The End

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ITI 1221. Introduction to Computing II Lab-7 Dewan Tanvir Ahmed University of Ottawa