CompSci Reading from Files  import java.io.File;  Declare a file File fileOfCats = new File(”cats.txt”);  Use file – pass it as an argument to a Scanner Scanner inscn = new Scanner(fileOfCats);

CompSci Using Scanner class to read  Import java.util.Scanner;  Look at API  Declare Scanner and bind it to a file (last slide)  Make sure there is input still to read while(inscn.hasNext())  Read next line String line = inscn.nextLine();  Read next word String word = inscn.next();

CompSci Look at LineNumberer  Snarf L0922  Look at LineNumber.java  Creates a File and a Scanner  Reads one line at a time, counts the lines and prints out the file with line numbers.

CompSci Why Inheritance?  Add new shapes easily without changing much code  Shape s1 = new Circle();  Shape s2 = new Square();  Abstract base class:  interface or abstraction  Function called at runtime  Concrete subclass  All abstract functions implemented  Later we'll override  “is-a” view of inheritance  Substitutable for, usable in all cases as-a shape mammal ScoreEntry FullHouse, LargeStraight User’s eye view: think and program with abstractions, realize different, but conforming implementations, don’t commit to something concrete until as late as possible

CompSci Example of Inheritance  What is behavior of a shape? void doShape(Shape s) { System.out.println(s.area()); System.out.println(s.perimeter()); s.expand(2.0); System.out.println(s.area()); System.out.println(s.perimeter()); } Shape s1 = new Circle(2); Shape s2 = new Square(4); Shape s3 = new Rectangle(2,5); doShape(s1); doShape(s2); doShape(s3);

CompSci Inheritance  Allows you to reuse code  Start with a Class (superclass or parent)  Create child class that extends the class (subclass)  The subclass can:  Use the methods from the superclass or  Override them (use the same name, but the code is different)  If the subclass redefines a superclass method, can still call the superclass method with the word “ super ” added.

CompSci Access to Instance Variables(state)  public  Any class can access  private  subclasses cannot access  protected  subclasses can access  other classes cannot access

CompSci Example (Lab today)  Student (superclass)  DukeStudent ( extends Student)  CosmicStudent ( extends DukeStudent)  Look at code, what is the output?