CompSci 6 12.1

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);

CompSci 6 12.2

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();

CompSci 6 12.3

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.

CompSci 6 12.4

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

ScoreEntryFullHouse, 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 6 12.5

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);

CompSci 6 12.6

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.

CompSci 6 12.7

Access to Instance Variables(state)

public Any class can access

private subclasses cannot access

protected subclasses can access other classes cannot access

CompSci 6 12.8

Example (Lab today)

Student (superclass) DukeStudent (extends Student) CosmicStudent (extends DukeStudent)

Look at code, what is the output?