Review Creating Objects

Peppermany references from

http://journals.ecs.soton.ac.uk/java/tutorial/java/objects/object.html

Objects you use

• Scanner • Random

ABC System.in

nextInt

nextDouble

next

Class blueprint Instance

• Scanner x = new Scanner(System.in)• int y = x.nextInt;

nextInt

nextDouble

next

Scanner Class

System.in 1223

nextInt

nextDouble

next

x

Input &Type

People class

say

moveArm

blink

People Class

mary

hair coloreye colorarm length

say

moveArm

blinkbrowngreen11

carrie

say

moveArm

blinkblondblue5

Creating a blueprint

• Add instance variables inside class and outside methods

public class Student{

private String hairColor;private String eyeColor;private int armLength;

/**}

Creating a blueprint

• remove static from methodspublic void printPerson ()

{

System.out.println ("The eye color is "+ eyeColor + " and the hair color is " + hairColor);

}

Use the blueprint

Student mary = new Student();Student carrie = new Student();mary.setEyeColor("green");mary.setHairColor("brown");carrie.setEyeColor("blue");carrie.setHairColor("blonde");

Look at the class again - thispublic void setEyeColor(String colorin) { this.eyeColor = colorin; }

mary

say

moveArm

blinkbrowngreen11

carrie

say

moveArm

blinkblondblue5

Exercise – make a point class

• setxy – take in 2 int to set x and y

• getx – return x• gety – return y• getDistance – take in

1 point and return distance to it

Point

gety

getx

setxyxy

getDistance 2122

12 yyxx

Make a point public class Point{ int x; int y; public void setxy (int xIn, int yIn) { this.x = xIn; this.y = yIn;} public int getx() { return this.x;} public int gety() { return this.y;} public double getDistance(Point another) { return Math.sqrt((this.x-another.getx()) * (this.x-another.getx()) + (this.y-another.gety()) * (this.y-another.gety())); }}

PointUsepublic class PointUse{ public static void main() { Point one = new Point(); Point two = new Point(); one.setxy(1,2); two.setxy(4,6); System.out.println(one.getDistance(two)); }}

Player class

setName

moveMan

getLoc

Player Class

locationnamescore

setLoc reportWin

setName

moveMan

getLoc

mary

30mary100

setLoc reportWin

setName

moveMan

getLoc

carrie

40carrie30

setLoc reportWin

Teach that player how to do things

• setName – take a string to change name• setLoc – take an int to change location• getLoc – return its loc• reportWin – print win if > 30• moveMan – take in int - amount to move; int - current loc ; return new loc

setName

moveMan

getLoc

Player Class

locationnamescore

setLoc reportWin

Player classpublic class Player{

int location; String name; int score;

public void setName(String namein){ this.name = namein;}public void setLoc(int locin){ this.location = locin;}public int setLoc(){ return this.location; }public boolean reportWin(){if (this.location > 30) { System.out.println(name + " won."); return true;} else {return false;}} public int moveMan(int move){ this.location = this.location+move; return this.location;}}

Game classpublic class Game1{ public static void main() { Player player1 = new Player(); Player player2 = new Player(); player1.setLoc(0); player2.setLoc(0); player1.setName("mary"); player2.setName("carrie"); player1.moveMan(15); player2.moveMan(13); player1.moveMan(12); player2.moveMan(20); player1.reportWin(); player2.reportWin(); }}

Summary So Far• Classes as Blueprints vs Instances

– Variable of a class type – hold instance– Create instances with new Class ()

• Behavior – methods– placement: same as other methods, not static– access: instance.method

• State – instance variables – placement: in class; outside method; – access: this.– scope: throughout class

Constructors

• Creates a new instance (a new object)• Can take in parameters so the new object

has information set inside it right away• Special method

– No return– Same name as the class

• Call it with "new" keyword

Point class constructorpublic class Point { int x; int y; //============ Constructor public Point(int x, int y) { this.x = x; this.y = y; }

Use the Point Constructor

Point myPoint = new Point(1,3);Point yourPoint = new Point(4,5);

myPoint

gety

getx

setxy13

getDistance

yourPoint

gety

getx

setxy45

getDistance

Constructors vs Methods• Differences between methods and constructors.

– There is no return type given in a constructor signature (header). The value is this object itself so there is no need to indicate a return value.

– There is no return statement in the body of the constructor. http://www.leepoint.net/notes-java/oop/constructors/constructor.html

What is wrong with this code

public class usePoint {public static void main(){Point myPoint1;Point myPoint2;System.out.println(myPoint1.getX());System.out.println(myPoint1.getDistance(myPoint2));}}

Summary So Far2• Classes as Blueprints vs Instances

– Variable of a class type – hold instance– Create instances with new Class () – default– Create instances with new Class (cons parms)

• Behavior – methods– placement: same as other methods, not static– access: instance.method– Special method: constructor

• State – instance variables – placement: in class; outside method; – access: this.– scope: throughout class