Interfaces: JAVA CONTRACTS

Transcription

1 Interfaces: JAVA CONTRACTS

2 Homework Stamp #3: Udacity Problem Set #6, # Quiz Question #2

3 Warm-Up

4 SuperFriends Video Game! You ve been hired to work on the brand-new Super Friends video game!

5 Mrs. Fronk wrote a SuperMan Class Her job was to create properties and behaviors that Superman would possess.

6 Mrs. D wrote a WonderWoman Class It has methods and instance variables that describe Wonder Woman.

7 Your Job: Class defeatprometheus You re in charge of a class that plays out a battle with the villain, Prometheus. Superman and Wonder Woman are both characters that players might use in this scene.

8 Fly!!! A big part of the battle involves the characters flying around Prometheus and attacking him. Superman flies by jumping into the air Wonder Woman uses a cool invisible plane to fly

9 You carve out time at 1AM to code You can t see Mrs. Fronk s code, or Mrs. Donaldson s code, but you know that you can instantiate a Superman Object and a WonderWoman Object using the default constructor Superman clarkkent = new Superman(); WonderWoman Diana = new WonderWoman() Now you re ready to make clarkkend and Diana fight Prometheus!

10 You start with Superman You try to make him fly by trying to guess the name of Mrs. Fronk's flying method : clarkkent.fly(); clarkkent.takeoff(); clarkkent.soar();.but nothing works :(

11 You have to CALL Mrs. F at 2:00 AM to ask what she named the method Oh! Sorry! It s called: itsabird() Now you know: clarkkent.itsabird();

12 Now you try the same thing for Wonder Woman WonderWoman Diana = new WonderWoman(); Diana.Fly(); Diana.ItsAPlane(); Diana.Invisible(); Nothing Works

13 Now you have to call Mrs. D Oh Sorry! It s invisiblejet() Now you can code! Clark.itsABird(); Diana.invisibleJet(); But that took WAY too long. Surely there s a better way...

14 Syntax : INTERFACE An INTERFACE is like a CONTRACT among programmers It s an agreed-upon list of methods and properties that a team uses when they re working on the same project. It establishes common names so that cooperation is easy.

15 Interface SuperHero public Interface Superhero { } public void fly(); public int gethealth(); //what are some other handy methods?? These are ABSTRACT methods, just suggestions. Each class that implements this interface must make them CONCRETE, or fully coded.

16 Syntax: implement A class implements an interface: class Superman implements Superhero //That means we know this class has a method called fly public void fly() { out.println ( I m a bird! I m a plane! I m Superman! ); }

17 WonderWoman and Batman, too: //Class Wonderwoman public void fly() { out.println ( Into the jet! ); } //Class Batman public void fly() { out.println ( My cape is out! ); }

18 Here s the cool part!!! If I add IMPLEMENT different classes with the SAME interface public class WonderWoman implements Superhero public class SuperMan implements Superhero public class Batman implements Superhero

19 THEN I can INSTANTIATE THEM ALL AS THE SAME TYPE OF INTERFACE Superhero diana = new WonderWoman(); Superhero clarkkent = new Superman(); Superhero brucewayne = new Batman();

20 And then I can put them in THE SAME array even though they are of different types! Superhero[] superfriends = new Superhero[3]; superfriends[0] = diana; superfriends[1] = clarkkent; superfriends[2] = brucewayne;

21 I can even skip the naming part and instantiate new Superheros like this Superhero[] superfriends = new Superhero[3]; superfriends[0] = new Superman(); superfriends[1] = new WonderWoman(); superfriends[2] = new Batman();

22 I can make them all fly because it s in the interface. The array will call each type s individual fly() method. Code SuperFriends[0].fly() SuperFriends[1].fly() Output It s a bird! It s a plane! It s Superman! Into the jet!

23 They can also call their GetHealth methods Code SuperFriends[1].getHealth() Output Wonder Woman is healthy and strong at 9/10 SuperFriends[2].getHealth() Batman is about to crash at 1/10!!!

24 Interfaces are a huge part of POLYMORPHISM Polymorphism s goal is to have the same method name work for many different types. It makes different types ACT alike.

25 AP TRICK!!!!! YOU CANNOT instantiate an interface NO: Superhero Diana = new Superhero(); //This means Diana only has abstract methods YES: Superhero Diana = new WonderWoman(); //This means Diana has her own Wonderful Way of performing the abstract methods in SuperHero The Interface on the right, Class Type on the left

26 Facts about interfaces - COPY 1) All methods in an interface must be abstract 2) All variables must be public static final (constant) 3) Interfaces cannot be instantiated 4) Interfaces cannot contain constructor methods 5) Interfaces are abstract classes - just ideas of what should happen 6) Classes may implement more than one interface

27 HOMEWORK 1) Do Interface Worksheet #1

28 Coding Bat: This one is tricky!

29 Warm-Up Let s Practice! You bought a zoo! Practice interfaces Learn about how.equals works

30 Grade FRQ - put in your log

31 Interface Comparable, Most Common public interface Comparable { int compareto(object obj) } //Any class that implements Comparable must include a method that compares objects of that class.

32 Why do we need comparable? It s important so that JAVA has a way to sort Objects. It s like equals

33 Sort Example Last week we talked about Monsters. Let s say that each Monster has 3 properties (instance variables) Name Height age Elmo 32 6 Cookie 48 4 Sully

34 Sort Example Monster[ ] monsters = new Monster[3]; monsters[0] = new Monster( Elmo, 32, 6); monsters[1] = new Monster( Cookie, 48, 4); monsters[2] = new Monster( Sully, 721, 38); monsters Elmo 32 6 Cookie 48 4 Sully

35 I want to sort the Monsters, but can t Arrays.sort(monsters); //this returns an error! What s the problem? monsters Elmo 32 6 Cookie 48 4 Sully

36 JAVA doesn t know how we want to sort Do we want to sort alphabetically by name? Or in increasing order by weight? Or in decreasing order by weight? Or sort by age? ACK! monsters Elmo 32 6 Cookie 48 4 Sully

37 We need to select our own sort critiera: Let s pick increasing order by age. Lower ages come before higher ages Let s write the code. monsters Elmo 32 6 Cookie 48 4 Sully

38 public int compareto(object o) { public int compareto(object obj) { Monster other = (Monster) obj; int difference = this.getage() -other.getage(); return difference; } monsters Elmo 32 6 Cookie 48 4 Sully

39 COPY Syntax - words in red ALWAYS THE SAME public int compareto(object obj) { Monster other = (Monster) obj; //cast to the type you re comparing int difference = this.getage() -other.getage(); //get the variable to compare return difference; } monsters Elmo 32 6 Cookie 48 4 Sully

40 Now one monster can compare himself to another! What would be output if Elmo is 6 and Cookie is 4 and Sully is 721? Elmo.compareTo(Cookie); Elmo.compareTo(Sully);

41 Even better to use the array monsters //What would be output? mosters[0].compareto(monsters[1]); mosters[0].compareto(monsters[1]); monsters Elmo 32 6 Cookie 48 4 Sully

42 NOW Collections.sort(monsters will work) Because the sort() method will know how to compare one monster to the other. If compareto() returns a positive number, sort will switch the elements. 6-4 = 2, so Elmo and Cookie will switch. monsters Elmo 32 6 Cookie 48 4 Sully

43 Is superman healthier than Wonder Woman? public int compareto(object obj) //Finds the difference in health points of 2 superheroes { Superhero other = (Superhero) obj; int difference = this.gethealth() - other.gethealth(); return difference; } //Runner. If Superman s health is 4 and WW s is 7, what would be returned? Clark.compareTo(Diana);

44 math Example of Interface: You write an interface when you know WHAT you want to be done without knowing HOW. public interface Circles { public abstract int findcircumference(object obj); //abstract implied, the word is optional private static final int pi = ; //variables must be private static final }

45 Combining Interfaces / public interface Locatable { public int getx(); public int gety(); } public interface Moveable { public void setpos(int x, int y); public void setx(int x); public void sety(int y); }

46 We can use them both! class Ship implements Locatable, Moveable { private int xpos, YPos; //How many methods have to be written? }

47 Fast Facts: Syntax All methods in an interface must be public abstract. All variables in an interface must be public static final An interface cannot be instantiated Interfaces cannot contain implemented (written)methods Interfaces are considered to be purely abstract classes

48 Homework: Interface worksheet #2 Class Complete Worksheet #9

49 Tomorrow! Multiple Choice test - 20 Questions on: Arrays of References Lists of References Study worksheets with those names ^^

50 Warm-Up: Defaults TYPE DEFAULT int double boolean String Object

51 Warm-Up: Defaults TYPE DEFAULT int 0 double 0.0 boolean String Object (any Object) false null null

52 Add a new Monster to monsterarray at 1 with age 5, weight 50, and name Boo public Monster (int a, int w, String n); {This is the constructor)

53 Add a new Monster to MonsterArray at 1 with age 5, weight 50, and name Boo Grover public Monster (int a, int w, String n); {This is the constructor) monsterarray[1] = new Monster(5, 50, Boo );

54 Add a new Monster to MonsterList with age 5, weight 50, and name Boo public Monster (int a, int w, String n); {This is the constructor)

55 Add a new Monster to MonsterArray with age 5, weight 50, and name Boo Grover public Monster (int a, int w, String n); {This is the constructor) monsterlist.add (new Monster(5, 50, Boo ));

56

57 Print the Weight of all the Monsters in monsterlist; Use a for-each

58 Print the Weight of all the Monsters For (Monster m:monsterlist) out.println(m.getweight());

59 TEST! 20MC Arrays/Lists of Objects

60 Lab Today Labs 19 Interfaces set 1 interfaces Interfaces Monster Lab 1 *Code In Canvas

61 Homework: Udacity PS 9, #1-8

62 Valentine Kahoot!

63 Warm-Up: Interface Kahoot! Interface 1 Interface 2

64 FRQ: Interfaces Do and turn in

65 Homework: Practice IT ODD ONLY

66 Homework 1) FRQ part b 2) MUST: Udacity Lesson #9 # ) RECOMMENDED FOR SERIOUS CODERS: #9-14 (Casting and checking for interfaces)

67 Warm Up! ax + by + c = 0, slope = -a/b 4x + 3y - 12 = 0 a) What is the slope of this line? b) Is the point (2,1) on this line?

68 Classwork : In Groups Answers on a piece of binder paper to turn in. 1) White multiple choice questions 2) 2010 FRQs, pink, #1 & 2

69 #1 answers a) int boxes = 0; for (CookieOrder o : orders) boxes += o.getnumboxes(); return boxes; } b) int boxesremoved = 0; for (int i = orders.size() - 1; i >= 0; i--) { if (orders.get(i).getvariety().equals(cookievar)) boxesremoved += orders.remove(i).getnumboxes(); ** } return boxesremoved; } **Could be 2 steps: boxesremoved += orders.get(i).getnumboxes(); orders.remove(i);

70 #2 public class APLine { private int a, b, c; public APLine(int a1, int b1, int c1) { a = a1; b = b1; c = c1; } public double getslope() { return -(a / ((double) b)); } public boolean isonline(int x, int y) { return a * x + b * y + c == 0; } }

71 #3 a) public boolean isleveltrailsegment(int start, int end) { int minelevation = markers[start]; int maxelevation = markers[start]; for (int i = start + 1; i <= end; i++) { if (markers[i] < minelevation) minelevation = markers[i]; if (markers[i] > maxelevation) maxelevation = markers[i]; } b) public boolean isdifficult() { int significantchanges = 0; for (int i = 1; i < markers.length; i++) if (Math.abs(markers[i - 1] - markers[i]) >= 30) significantchanges++; return significantchanges >= 3; } return maxelevation - minelevation <= 10; }

72 Homework!!! FRQ 2014 #1 part b