Reading from Files

1. 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);

2. 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();

3. 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.

4. 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

5. 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);

6. 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.

7. Access to Instance Variables(state) • public • Any class can access • private • subclasses cannot access • protected • subclasses can access • other classes cannot access

8. Example (Lab today) • Student (superclass) • DukeStudent (extends Student) • CosmicStudent (extends DukeStudent) • Look at code, what is the output?