CSC7322: Object Oriented Development. J Paul Gibson, A207.

Transcription

1 CSC7322: Object Oriented Development J Paul Gibson, A207 paul.gibson@telecom-sudparis.eu Design (In Java) /~gibson/teaching/csc7322/l3-design(in Java).pdf 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.1

2 DISCUSSION: What is (software) design? There are two ways of constructing a software design. One way is to make it so simple that there are obviously no deficiencies. And the other way is to make it so complicated that there are no obvious deficiencies. C.A.R. Hoare 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.2

3 Some reading material on design (in general) Notes on structured programming. Dijkstra, E.W., On the criteria to be used in decomposing systems into modules, Parnas, David Lorge, 1972 A guided tour of program design methodologies, Bergland, Glenn D., Foundations for the Study of Software Architecture, Dewayne E. Perry and Alexander L. Wolf, 1992 The pragmatics of model-driven development, Selic, Bran Domain-Driven Design: Tackling Complexity in the Heart of Software, Eric Evans, : J Paul Gibson TSP: Object Oriented Development CSC7322/Design.3

4 Design: the bridge between the problem and the solution Discussion: How often does software fail because the design bridge collapses? 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.4

5 Good design is all about experience: Recognising a problem s structure and knowing about alternative solutions (designs) to meeting the requirements of the problem Knowing about implementation issues specific to potential implementation languages/architectures Good judgement is the result of experience Experience is the result of bad judgement. Fred Brooks Realising that there is often not a perfect fit between the design and the target implementation language/architecture Being able to adapt the design to the language and/or adapt the language to the design Note: in OO we may consider the library to be part of the language Let us return to the Dice problem with this in mind. 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.5

6 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.6

7 public interface DiceSpecification extends HasInvariant{ * The minimum number of sides for a Dice as specified in the requirements<br> final static int MINIMUM_numberOfSides = 3; * The maximum number of sides for a Dice as specified in the requirements final static int MAXIMIM_numberOfSides = 36; * The default number of sides for a Dice as specified in the requirements final static int DEFAULT_numberOfSides = 6; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.7

8 * True if the <code> MAXIMIM_numberOfSides </code>, <code>minimum_numberofsides</code> and * <code> DEFAULT_numberOfSides </code> values for the number of sides of the Dice * are coherent/valid, * otherwise false DiceSpecification#invariant() boolean INVARIANT_OF_CLASS = ( MAXIMIM_numberOfSides >= MINIMUM_numberOfSides && MINIMUM_numberOfSides >0 && DEFAULT_numberOfSides >= MINIMUM_numberOfSides && DEFAULT_numberOfSides <= MAXIMIM_numberOfSides); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.8

9 * Check that the Dice object is in a safe (meaningful) state * true if * <ul> * <li> <ul><li> once the Dice is rolled, the last roll is within range * 1... <code> NUMBEROFSIDES </code></li>, or * <li> if the Dice is yet to be rolled then the last roll value is zero, </li> * </ul> and </li> * <li> the <code> numberofrolls</code> is non-negative, and * </li><li> the number of sides of dice is within range * <code> MINIMUM_numberOfSides </code>... <code> MAXIMUM_numberOfSides</code> * </li> * </ul> * otherwise false * DiceSpecification#INVARIANT_OF_CLASS boolean invariant(); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.9

10 * Getter method for <code> NUMBEROFSIDES</code> * the number of sides of the Dice int numberofsides(); * Getter method for <code> numberofrolls</code> * the number of times the Dice has been rolled since it was constructed int numberofrolls(); * Getter method for reading the value of the <code> lastroll </code><br> * the lastroll value int lastroll (); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.10

11 * Updates the last roll to a random value between 1 and the number of sides, * and increments the roll count. * InvariantBroken if Dice is no longer in a safe state void roll() throws InvariantBroken; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.11

12 The current state of the Dice as a String<br> * The format to be followed is, eg:<br> * <pre> 6-sided Dice - lastroll = 1. (Total number of rolls = 10) * </pre> public String tostring(); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.12

13 thing is the Object to test for equality true if * <ul> * <li> the two objects reference the same address, or * <li> the thing is a Dice and there is equality on * <code> lastroll</code> and <code> NUMBEROFSIDES</code> fields * </ul> * otherwise false public boolean equals(object thing); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.13

14 thing is the Object to test for equality true if * <ul> * <li> the two objects reference the same address, or * <li> the thing is a Dice and there is equality on * <code> lastroll</code> and <code> NUMBEROFSIDES</code> fields * </ul> * otherwise false public boolean equals(object thing); NOTE: Don t forget to over-ride the hashcode method If two objects are equal by equals() method then the result returned by the hashcode() method must be same. Multiple invocations on same object (that doesnt change state) must return the same result during a single execution; but can differ between executions (!) 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.14

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16 public abstract class DiceAbstraction implements DiceSpecification{ public boolean equals( Object thing){ if (thing ==null) return false; if ( this == thing) return true; if (! (thing instanceof DiceAbstraction)) return false; DiceAbstraction that = (DiceAbstraction) thing; return ( (this.lastroll() == that.lastroll()) && (this.numberofsides() == that.numberofsides()) ); public String tostring(){ String str =""; str = str+ numberofsides()+"-sided Dice - lastroll = "+lastroll()+ ". (Total number of rolls = "+numberofrolls()+")"; return str; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.16

17 * Algorithm taken from Josh Bloch's "Effective Java", using primes 37 and 41 * <ul> * <li> initialise with prime = 37</li> * <li> for each field tested in {@link DiceAbstraction#equals increase * iteratively with another prime multiplier: * hash = 41 * hash + field_integer_value </li> * </ul> * public int hashcode(){ int hash = 37; // start with a prime hash = 41 * hash + lastroll(); // iteratively increase with another prime multiplier hash = 41 * hash + numberofsides(); return hash; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.17

18 public boolean invariant(){ return (( (numberofrolls() == 0 && lastroll() == 0 ) (numberofrolls() > 0 && lastroll()>0 && lastroll()<=numberofsides() ) )&& (numberofsides()>=minimum_numberofsides) && (numberofsides() <= MAXIMIM_numberOfSides) ); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.18

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20 public class Dice extends DiceAbstraction implements DiceSpecification{ // The javadocs are in the code removed here for easier presentation public final int NUMBEROFSIDES; protected Random rng = new Random(); protected static int numberofdie = 0; protected int numberofrolls = 0; protected int lastroll = 0; public boolean invariant(){ return super.invariant() && rng!=null; // We saw constructors in previous lecture 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.20

21 public int lastroll (){ return lastroll; public int numberofsides(){ return NUMBEROFSIDES; public int numberofrolls(){ return numberofrolls; * Getter method for the static <code> numberofdie </code> the number of Die that have been constructed public static int numberofdie(){ return numberofdie; QUESTION : Why is the static method not specified in the interface or abstract class? 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.21

22 * Setter method for the random number generator local to the dice<br> * * Tested by {@link JUnit_DiceTest#testSetRNGException, which shows that * we do not need to check invariant as any invalid change to rng is caught * rng is the new random number generator to be used when rolling the dice IllegalArgumentException if argument <code> rng </code> is <code>null</code> public void setrng( Random rng) throws IllegalArgumentException{ if (rng==null) throw (new IllegalArgumentException("Cannot set rng to null")); this.rng = rng; // if (!invariant()) throw (new InvariantBroken("Dice is no longer in a safe state")); * Tested by {@link JUnit_DiceAbstractionTest#testRoll, which guarantees that the Dice is * constructed in a safe state as specified by {@link Dice#invariant. * public void roll() throws InvariantBroken{ lastroll = rng.nextint(numberofsides)+1; numberofrolls++; // if (!invariant()) throw (new InvariantBroken("Dice is no longer in a safe state")); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.22

23 @Before public abstract void setup() throws public abstract void teardown() throws Exception; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.23

24 public class JUnit_DiceTest extends public void setup() throws Exception { dicedefault = new Dice(); dicenondefaultok = new Dice((Dice.MAXIMIM_numberOfSides + Dice.MINIMUM_numberOfSides)/2); dicenondefaultko = new Dice(Dice.MAXIMIM_numberOfSides + 1); dicerolledtwice = new Dice(); dicerolledtwice.roll(); dicerolledtwice.roll(); dicecopyrolledtwice = new Dice ( (Dice) dicerolledtwice); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.24

25 * test exception in = IllegalArgumentException.class) public void testsetrngexception() { ((Dice) dicedefault).setrng(null); * test {@link Dice#numberOfDie() by creating 10 new die and checking public void testnumberofdie() { int countnumberofdie = Dice.numberOfDie(); final int NUMBER_OF_DIE_TO_CONSTRUCT = 10; for (int i=0; i<number_of_die_to_construct; i++) new Dice(); Assert.assertEquals(countNumberOfDie+NUMBER_OF_DIE_TO_CONSTRUCT, Dice.numberOfDie()); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.25

26 WARNING: All green does not always mean that all is well! DISCUSSION: Why not? 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.26

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28 public class Random_DiceTest { protected static Dice dice = new Dice(); public static void main(string[] args) { * The number of rolls in our simulation final int NUMBER_OF_TEST_ROLLS = 6; Random rng = SeedRNGCommandLine.getRandom(args); System.out.println(DateHeader.dateString()); System.out.println(dice); dice.setrng(rng); System.out.println("Rolling "+NUMBER_OF_TEST_ROLLS+ " times"); for (int i =1; i<=number_of_test_rolls;i++){ dice.roll(); System.out.println(i+". Roll = " +dice.lastroll() ); System.out.println(dice); 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.28

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30 TO DO: Create a new class which adds statistics to the dice This class should add functionality to store the roll frequencies. You should implement a validation test (as well as running unit tests) as below: NOTE: Don t forget to run regression tests 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.30

31 TO DO: Implement 2 different designs //using inheritance public class DiceWithStatistics1 extends Dice implements DiceWithStatisticsSpecification{ //using composition public class DiceWithStatistics2 implements DiceWithStatisticsSpecification{ protected Dice dice; 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.31

32 TO DO: Create 2 different terminal/console views The frequencies can either be displayed vertically or horizontally. If the frequency values are bigger than the height/width of the screen then you should scale them in order to occupy as much of the screen as possible. The screen size should be stored in constant variables HEIGHT and WIDTH. 1 ******** 2 ****** 3 *** 4 **** 5 ****** 6 ** 7 *** 8 ** 9 ***** ***** 12 ** 13 ******** 14 ***** 15 ********* * * * * * * * * * * * * * * * * * * * * ** * * * ** * * * ** * * * *** ** ** * * *** ** ** * * *** ***** * * * *** ***** * * * *** ********* ***** ********* ***** ********* ***** ********* ***** ********* ***** DISCUSSION: How to best include these views in the design? 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.32

33 The consequences of the initial design decision Choosing to implement a DiceWithStatistics as a subclass of Dice is a design decision that may have consequencies on later stages of the development. The alternative re-use mechanism was to design a DiceWithStatistics class/object to have a Dice component class/object. This also may have consequencies on later stages of the development DISCUSSION: What are the possible consequences (positive and negative)? CLUE: You may have seen them when we considered the different views OBSERVERS: We may wish to create different views that automatically update when the state of the models changes 2013: J Paul Gibson TSP: Object Oriented Development CSC7322/Design.33