12a-interfaces

# 12a-interfaces - CSE 143 Lecture 12(A Interfaces reading 9.5 11.1 slides created by Marty Stepp http/www.cs.washington.edu/143 Related classes

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CSE 143 Lecture 12 (A) Interfaces reading: 9.5, 11.1 slides created by Marty Stepp http://www.cs.washington.edu/143/

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2 Related classes • Consider the task of writing classes to represent 2D shapes such as Circle , Rectangle , and Triangle . • Certain operations are common to all shapes: – perimeter: distance around the outside of the shape – area: amount of 2D space occupied by the shape – Every shape has these, but each computes them differently.
3 Shape area and perimeter • Circle (as defined by radius r ): area = π r 2 perimeter = 2 π r • Rectangle (as defined by width w and height h ): area = w h perimeter = 2w + 2h • Triangle (as defined by side lengths a, b, and c) area = (s (s - a) (s - b) (s - c)) where s = ½ (a + b + c) perimeter = a + b + c r w h a b c

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4 Common behavior • Suppose we have 3 classes Circle , Rectangle , Triangle . – Each has the methods perimeter and area . • We'd like our client code to be able to treat different kinds of shapes in the same way: – Write a method that prints any shape's area and perimeter. – Create an array to hold a mixture of the various shape objects. – Write a method that could return a rectangle, a circle, a triangle, or any other kind of shape. – Make a DrawingPanel display many shapes on screen.
5 Interfaces (9.5) interface : A list of methods that a class can promise to implement. – Inheritance gives you an is-a relationship and code sharing. •A Lawyer can be treated as an Employee and inherits its code. – Interfaces give you an is-a relationship without code sharing.

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## This note was uploaded on 01/04/2011 for the course CSE 143 taught by Professor Sr during the Spring '08 term at University of Washington.

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12a-interfaces - CSE 143 Lecture 12(A Interfaces reading 9.5 11.1 slides created by Marty Stepp http/www.cs.washington.edu/143 Related classes

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