Objects

Peppermany references from

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

Objects

• Look around you and see objects – desk, people, blackboard, pen, eraser

• State – hair color, eye color, name, arm length, mouth expression

• Behavior – move arm; speak; see

variables and methods

Bicycle object

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 methods

public 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

Step 1: Class with Variables

Create a class called point

Create 2 class instance variables

int x

int ypublic class Point{ int x; int y;}(Note, you can create int x = 1; if you want 1 to be the default value when the Point is created.

2: Create a method to set x, y

Method name: setxyInput: int for x, int for yOutput: noneRequires class instance: Yes

public void setxy (int xIn, int yIn) { this.x = xIn; this.y = yIn;}

3: Create a method to get the x

Method name: getxInput: noneOutput: int (the x value of the point)Requires class instance: Yes

public int getx() { return this.x;}

public int gety() { return this.y;}

4: Create a method to get Distance

Method name: getDistanceInput: another pointOutput: double representing distanceRequires class instance: YesProcess:

2122

12 yyxx

4: Create a method to get Distance

public double getDistance(Point another) { int x1 = another.getx(); int y1 = another.gety();

return Math.sqrt((this.x-x1) * (this.x-x1) + (this.y-y1) * (this.y-y1)); }

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())); }}

Use your point class

• create 2 points

• print the distance between them

PointUse

public 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

exercise – make a player

• Make a player that knows its own – location - int– name - String– score - int

setName

moveMan

getLoc

Player Class

locationnamescore

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;}}

Exercise continued - Make a game class

• Main method

• Create 2 players

• Tell players their names

• Tell players to start on 0

• Tell players to move some amounts

• Ask each player if it won

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

coming soon

• Class variables - shared variables among instances

• Class constants - variables that do not change for the class

http://docs.oracle.com/javase/tutorial/java/javaOO/classvars.html