Week 13 - Wednesday

 What did we talk about last time?  Color representation  Color class  Picture class

 Straightforward idea  Flip an image around the y-axis  Maybe you want to decipher some of Leonardo’s writings  No, the other one

 Given an image with width w and height h:  Moving from left to right in the original image, copy each column, storing each column from right to left in the new image

012 0 A 1 B 2 C 3 D A 1 B 2 C 3 D OriginalMirrored

 What would the code for mirroring look like? Picture picture = new Picture( file ); //the picture to be mirrored Picture mirrored = new Picture( picture.width(), picture.height() ); for( int i = 0; i < picture.width(); i++ ) for( int j = 0; j < picture.height(); j++ ) mirrored.set( picture.width() - i - 1, j, picture.get( i, j ) ); Picture picture = new Picture( file ); //the picture to be mirrored Picture mirrored = new Picture( picture.width(), picture.height() ); for( int i = 0; i < picture.width(); i++ ) for( int j = 0; j < picture.height(); j++ ) mirrored.set( picture.width() - i - 1, j, picture.get( i, j ) );

 Pretty much the same thing  Instead of copying each column in reverse order, copy each row in reverse order

 Another straightforward idea  Necessary if you are writing software for a digital camera (the user might turn the camera for portrait instead of landscape)

 Given an image with width w and height h:  Create a new image with width h and height w  Copy each column in the original image into a row in the new image, remembering to move back along the row

012 0 A 1 B 2 C 3 D DCBA 1 2 Original Rotated

 What would the code for a rotation look like? Picture picture = new Picture( file ); //the picture to be rotated Picture rotated = new Picture( picture.height(), picture.width() ); for( int i = 0; i < picture.width(); i++ ) for( int j = 0; j < picture.height(); j++ ) rotated.set( picture.height() - j - 1, i, picture.get( i, j ) ); Picture picture = new Picture( file ); //the picture to be rotated Picture rotated = new Picture( picture.height(), picture.width() ); for( int i = 0; i < picture.width(); i++ ) for( int j = 0; j < picture.height(); j++ ) rotated.set( picture.height() - j - 1, i, picture.get( i, j ) );

 Rotating 180°, 270°, -90°, -180°, or -270° can be done using similar techniques or simply performing right rotations multiple times  Rotations that are not multiples of 90° are much trickier, result in non-rectangular final images, and need some trigonometry  Don’t worry about rotations that are not multiples of 90°

 You’ve seen this many times before  Sometimes an image won’t fit nicely in on a PowerPoint slide

 Let's just focus on growing, because that's what you need to do in your project  If we are just doubling the image, we create a new image whose width and height are twice the original  Then, we go through the new image, copying the pixels from the original using pixels whose column and row are half as big as the ones we are putting into the new image

 Doubling an image  Each old pixels maps to four new ones AABB 1 AABB 2 CCDD 3 CCDD 01 0 AB 1 CD

 This kind of resize works, but is crude  To shrinking an image, a clever resize might average together pixels  When growing an image, different techniques can be done to fill in “guesses” for pixels that sit between pixels from the original image, instead of just duplicating them  People who program Photoshop have thought long and hard about how to do these tasks better

 The idea of inheritance is to take one class and generate a child class  This child class has everything that the parent class has (members and methods)  But, you can also add more functionality to the child  The child can be considered to be a specialized version of the parent

 The key idea behind inheritance is safe code reuse  You can use old code that was designed to, say, sort lists of Vehicle s, and apply that code to lists of Car s  All that you have to do is make sure that Car is a subclass (or child class) of Vehicle

 Java respects the subclass relationship  If you have a Vehicle reference, you can store a Car object in that reference  A subclass (in this case a Car ) is a more specific version of the superclass ( Vehicle )  For this reason, you can use a Car anywhere you can use a Vehicle  You cannot use a Vehicle anywhere you would use a Car

 As long as Car is a subclass of Vehicle, we can store a Car in a Vehicle reference  Even in an array is fine  Storing a Vehicle into a Car doesn’t work Vehicle v = new Car("Lancer Evolution"); // perfectly okay Vehicle v = new Car("Lancer Evolution"); // perfectly okay Vehicle[] vehicles = new Vehicle[100]; for( int i = 0; i < vehicles.length; i++ ) vehicles[i] = new RocketShip(); // cool Vehicle[] vehicles = new Vehicle[100]; for( int i = 0; i < vehicles.length; i++ ) vehicles[i] = new RocketShip(); // cool Car c = new Vehicle(); // gives error

 All this is well and good, but how do you actually create a subclass?  Let’s start by writing the Vehicle class public class Vehicle { public void travel(String destination) { System.out.println("Traveling to " + destination); } public class Vehicle { public void travel(String destination) { System.out.println("Traveling to " + destination); }

 We use the extends keyword to create a subclass from a superclass  A Car can do everything that a Vehicle can, plus more public class Car extends Vehicle { private String model; public Car(String s) { model = s; } public String getModel() { return model; } public void startEngine() { System.out.println("Vrooooom!"); } public class Car extends Vehicle { private String model; public Car(String s) { model = s; } public String getModel() { return model; } public void startEngine() { System.out.println("Vrooooom!"); }

 There is a part of the Car class that knows all the Vehicle members and methods Car car = new Car("Camry"); System.out.println( car.getModel() ); //prints "Camry" car.startEngine(); //prints "Vrooooom!" car.travel( "New York City" ); //prints "Traveling to New York City" Car car = new Car("Camry"); System.out.println( car.getModel() ); //prints "Camry" car.startEngine(); //prints "Vrooooom!" car.travel( "New York City" ); //prints "Traveling to New York City"

 Each Car object actually has a Vehicle object buried inside of it  If code tries to call a method that isn’t found in the Car class, it will look deeper and see if it is in the Vehicle class  The outermost method will always be called Car model getModel() startEngine() Car model getModel() startEngine() Vehicle travel() Vehicle travel()

 Sometimes you want to do more than add  You want to change a method to do something different  You can write a method in a child class that has the same name as a method in a parent class  The child version of the method will always get called  This is called overriding a method

 We can define the Mammal class as follows: public class Mammal { public void makeNoise() { System.out.println("Grunt!"); } public class Mammal { public void makeNoise() { System.out.println("Grunt!"); }

 From there, we can define the Dog, Cat, and Human subclasses, overriding the makeNoise() method appropriately public class Dog extends Mammal { public void makeNoise() { System.out.println("Woof"); } } public class Dog extends Mammal { public void makeNoise() { System.out.println("Woof"); } } public class Cat extends Mammal { public void makeNoise() { System.out.println("Meow"); } } public class Cat extends Mammal { public void makeNoise() { System.out.println("Meow"); } } public class Human extends Mammal { public void makeNoise() { System.out.println("Hello"); } } public class Human extends Mammal { public void makeNoise() { System.out.println("Hello"); } }

 Inheritance examples  Lab 13

 Start working on Project 5