Announcements Announcements For Monday read Becker sections 1 4-1 - - PowerPoint PPT Presentation

Announcements Announcements

• For Monday read Becker sections 1 4-1 8

For Monday, read Becker, sections 1.4-1.8

• Fill out the Questionnaire in MS Word format

and then email it to me (kwsuh@ilstu edu) by and then email it to me (kwsuh@ilstu.edu) by Friday h //bl kb d il d

• http://blackboard.ilstu.edu
• Lab 2

– Course Web Site: http://www.itk.ilstu.edu/itk168 – Section Web Site: http://www.itk.ilstu.edu/faculty/kwsuh/courses/ITK168/Fall2011/index.ht m

Chapter 1 Objectives Chapter 1 Objectives

• Describe what models are

Describe what models are

• Describe the relationship between objects and

classes

• Understand the syntax and semantics of a

simple Java program p p g

• Write object-oriented programs that simulate

robots

• Understand and fix errors in programs
• Read/use documentation for classes (API)

( )

Modeling with Objects

Model Information Operations

Concert Who’s performing Performance date Sell a ticket Count tickets sold Which seats are sold Schedule List of task, each with est. Insert or delete a task time Calc est. finish time Restaurant Occupied tables Mark a table Restaurant seating Occupied tables Unoccupied tables # of seats at each table Mark a table

• ccupied

Mark a table # o seats at eac tab e unoccupied

Using Models Using Models

• A model is a simplified description of

A model is a simplified description of something that is used to

– Make decisions – Predict future events – Maintain up-to-date information p – Simulate a process – Answer questions

• Change over time
• Form an abstraction
• Provide operations to be performed

Abstraction Abstraction

• The key to dealing with complexity

The key to dealing with complexity

• Focus only on relevant information

O i d t il i t f l hi h l l

• Organize details into useful higher-level

chunks

• Eliminate and hide some details
• Group similar details together in chunks

p g

Using Software Objects to Create Models Create Models

• A program is a detailed set of instructions

A program is a detailed set of instructions

• Java is an object-oriented language

U ft bj t th t d t – Uses software objects that correspond to an identifiable entity in the problem

Software Objects Software Objects

• Maintain information called attributes

Maintain information called attributes

• Answer questions based on that

information using queries information using queries

• Change the information using commands
• Queries and commands are collectively

called services

• Services are provided to clients

Objects Objects

• Based on a “template” called a class

Based on a template called a class

• Have the same attributes and services

Att ib t h diff t l

• Attributes have different values
• Services are the same for all objects of the

same class

Class Definitions Class Definitions

• This is what we code in a Java program

This is what we code in a Java program

• Used to create multiple objects

C ll d i t f th l – Called instances of the class

• Specifies attributes and services
• Class – vs – Object

– Blueprint – house p – Pattern – dress – Cookie cutter - cookie

Queries and Attributes Queries and Attributes

• A query is always answered by the object

A query is always answered by the object

– True or false A number – A number – A string of characters

A b d th bj t’

• Answers are based on the object’s

attributes (therefore possible questions li it d) are limited)

Commands Commands

• Change the value of an attribute (or

Change the value of an attribute (or attributes) to reflect a new reality

• Can be visualized using a state of
• Can be visualized using a state of

change diagram

St t f th bj t b f – State of the object before – State of the object after

Class Diagram Class Diagram

• Rectangle with 3 sections

Rectangle with 3 sections

– Name of class List of attributes – List of attributes – List of services

• Sometimes class diagrams do not list the

attributes

– Black-box programming

Modeling Robots Modeling Robots

• Book author provides many classes in a

Book author provides many classes in a package called – becker.jar

• Basic enough to grasp easily
• Basic enough to grasp easily
• Complex enough to be interesting
• Simple enough to be easy to program
• Rich enough to demonstrate OOP

g concepts

Karel’s World Karel s World

• City – rectangular grid

City rectangular grid

• Streets – run east and west
• Avenues – run north and south

Avenues run north and south

• Streets and avenues start numbering at zero

(typical in programming) (typical in programming)

• Robots and other objects are placed at the

intersections – listed as ordered pairs te sect o s sted as o de ed pa s

– (1, 2) = street 1, avenue 2 – Multiple robots and things can occupy the same intersection

Walls and Things Walls and Things

• Intersections may be surrounded by walls

Intersections may be surrounded by walls

• Walls block robots

I t ti h “thi ” (l ft

• Intersections may have “things” (left non-

descript to be identified as needed – b l t t ) paper, box, plant, etc)

• Typically, things do not block robots

Robots Robots

• Exist to serve clients

Exist to serve clients

• Perform 4 services

– Move Move – Turn – Pick things up Pick things up – Put things down

• Answer queries about their location and

Answer queries about their location and direction

• Respond to commands – such as

Respond to commands such as controlling speed

Incomplete Class Diagram Incomplete Class Diagram

Robot

• street: int
• avenue : int
• direction: Direction
• backpack: ThingBag

+ Robot(City aCity, int aStreet, int anAvenue, Direction aDirection) + move(): void t L ft() id + turnLeft(): void + pickThing(): void + putThing(): void + putThing(): void

Class Details Class Details

• Attributes

Al i t ( ) – Always private (-) – Name – Type

• Constructors

Constructors

– Always public (+) – Used to build objects – No return type S th l – Same name as the class – May or may not have parameter list

• Default constructor
• Special constructor
• Services

– Public (+), private (-), or protected (#) – Name Parameter list – Parameter list – Return type

Services Services

• A robot performs a service only when it is

p y invoked by a corresponding message

– turnLeft – turns 90 degrees to the left remaining on the same intersection the same intersection

• Turning is a safe activity

– move – attempts to move forward one intersection still facing in the same direction – pickThing – attempts to pick up a thing from the current intersection – putThing – attempts to put a thing down in the current intersection

• Moving picking up and putting down objects are not always
• Moving, picking up, and putting down objects are not always

safe activities

Messages Messages

Argument list “dot” Argument list aka: parameter list

karel.move();

semicolon Reference to the

• bject

The service to execute semicolon j aka: variable aka: method

Example Program Example Program

• Situation

Situation

– A delivery robot is to pick up a parcel, represented by a Thing at intersection (1 2) represented by a Thing, at intersection (1,2) and deliver it to (2,3) Initial state Final state

The Java Program The Java Program

import becker.robots.*; public class DeliverParcel { pub c c ass e e a ce { public static void main(String[] args) { //Set up the initial situation City prague = new City(); Thing parcel = new Thing(prague, 1, 2); g p g(p g , , ); Robot karel = new Robot(prague, 1, 0, Direction.EAST); //Direct the robot to the final situation karel.move(); (); karel.move(); karel.pickThing(); karel.move(); karel.turnLeft(); //start turning right as 3 lefts (); // g g karel.turnLeft(); karel.turnLeft(); //finished turning right karel.move(); karel.putThing(); p g(); karel.move(); } }

Sketch the initial state and final state of this program

import becker.robots.*; public class GoAroundRoadBlock p { public static void main(String[] args) { //set up initial situation City ny = new City(); Wall blockAve0 = new Wall(ny, 0, 2, Direction.WEST); ll bl k 1 ll( 1 2 i i ) Wall blockAve1 = new Wall(ny, 1, 2, Direction.WEST); Robot mark = new Robot(ny, 0, 2, Direction.WEST); Robot ann = new Robot(ny, 0, 1, Direction.EAST); //what does mark do here? mark turnLeft(); mark.turnLeft(); mark.move(); mark.move(); mark.turnLeft(); mark.turnLeft(); mark.turnLeft(); mark.move(); //what does ann do here? ann.turnLeft(); ann.turnLeft(); t L ft() ann.turnLeft(); ann.move(); ann.move(); ann.turnLeft(); } }

Reading Documentation Reading Documentation

• www.learningwithrobots.com

– www.learningwithrobots.com/doc/index.html

• http://download.oracle.com/javase/6/docs/api/ or
• http://download.oracle.com/javase/7/docs/api/

p j p

Errors Errors

• Compile-time errors

Compile time errors

– Also known as syntax errors

• Run-time errors

Run time errors

– Results of instructions executing in an illegal context (e.g., crashing a robot into a wall)

• Intent errors

– Also known as logic error – occurs when program fails to carry out its intended purpose – no compilation or run-time errors but fail to – no compilation or run-time errors, but fail to accomplish the job

Compile-time Errors Compile time Errors

• Program breaks some rules of Java

Program breaks some rules of Java

• Examples

L i t th i l b – Leaving out parentheses, semi-colons, braces – Misspelling words C ( ) – Capitalization wrong (Java is case-sensitive)

• Discovered because the compiler points

them out

Run-time Errors Run time Errors

• Program compiles correctly and starts to

Program compiles correctly and starts to run but reaches an error state and stops

• Examples:
• Examples:

– Robot runs into a wall R b t t i t t thi d h it – Robot tries to put a thing down when it doesn’t have one R b t t i t i k thi b t th ’ – Robot tries to pick something up, but there’s nothing there

Intent Errors Intent Errors

• Programs run fine but doesn’t actually

Programs run fine, but doesn t actually work

• What if we forgot to make a robot turn left
• What if we forgot to make a robot turn left

in the relay race program? Th t t h d t i d

• These are not too hard to recognize and

fix in the robot world, but can be quite h ll i i th ki d f challenging in other kinds of programs.

Software Patterns Software Patterns

• Intended to help you learn and generalize

Intended to help you learn and generalize.

• Not to be skipped over and ignored.

Basic Java Patterns Basic Java Patterns

• Java Program Pattern

Java Program Pattern

• Object Instantiation Pattern

C d I ti P tt

• Command Invocation Pattern
• Sequential Execution Pattern

Planting Flowers

• You have a square enclosure. You want to

have a robot plant flowers (Things) around the enclosure See below the enclosure. See below. Questions: Ho man alls are there? Ho are the positioned? How many walls are there? How are they positioned? Where do the flowers come from?

Beyond Robots Beyond Robots

• Objects are used in all contexts in Java

Objects are used in all contexts in Java programs.

• The same patterns are used to develop
• The same patterns are used to develop

GUI (Graphical user interface) programs as to develop Robot programs as to develop Robot programs.

• However, the classes we use are different.

Sample Simple GUI

• Use the JFrame, JLabel, JTextField, and

JTextArea classes to produce a program that g creates a window that looks like a browser window (sort of).

End of Chapter End of Chapter

• Be sure to study the patterns listed at the

Be sure to study the patterns listed at the end of each chapter

• You will be expected to understand them
• You will be expected to understand them
• Likewise, study the concept map at the

d f h h t end of each chapter

• Download and complete the exercise set

posted on the course web site