Lecture Slides on Programming with Objects | CSCE 145, Study notes of Computer Science

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Java:Learning to Program with RobotsChapter 01: Programming with Objects

After studying this chapter, you should be able to: • Chapter Objectives Describe models • Describe the relationship between objects and classes • Understand the syntax and semantics of a simple Java program • Write object-oriented programs that simulate robots • Understand and fix errors that can occur when constructing aprogram • Read documentation for classes • Apply the concepts learned with robots to display a window as usedin a graphical user interface

• 1.1.2: Using Software Objects to Model Java programs are composed of software objects^ • Software objects have:

•^

Information, called

attributes

•^

Services

that either change the attributes (a

command

) or

answer a question about attributes (a

query

•^

A program may havemany similar objects

-^ Objects can bevisualized with an object diagram

•^

shows attributenames and values

Conc ert d ate: 28 -M arch-20 08 perfo rm er: To ro nto Sym ph on y un so ld Tick ets : 35 A, 35 B, 3 5Cso ld Tick ets : 10 A, 10 B, ..., 3 4Z , ...

35 D, ...

Conce rt date: 2 1-M arch-20 08 p erfo rm er: Great B ig Sea un so ld Tickets : 1 0D, 22 H , 2 5A ,

2 5B, 25 C, 28 Z ,...

Sold Seats : 1 0A, 10 B, 10 C,

..., 22 N, 2 2P , ...

Conc ert date: 22 -M arch-2 00 8 perform er: Great Big Sea u ns oldT ickets: 35 A, 3 5B, 35 Cs oldT ickets: 10 A, 1 0B, ..., 34 Z ,

... 35D , ...

Type ofobject Attributevalues

Attributenames

• 1.1.2: Using Software Objects to Model A group of objects that

•^

have the same kind of information

-^ offer the same services are called a

class

•^

Classes arerepresented with a class diagram

Concert

dateperformerunsoldTicketssoldTicketsConcert(date, performer)numTicketsSold( )valueOfTicketsSold( )performerName( )performanceDate( )sellTicket(seatNumber)

Name ofthe class Attributes Services

Quick Quiz

1.Draw an object diagram for the robot labelled “M”on the previous slide.Hint: Three

Concert

object diagrams areshown to the right. 2.Draw your object diagram again after the robot hasexecuted the followingcommands: move()pickThing()

Conc ert d ate: 28 -M arch-20 08 perfo rm er: To ro nto Sym ph on y un so ld Tick ets : 35 A, 35 B, 3 5Cso ld Tick ets : 10 A, 10 B, ..., 3 4Z , ...

35 D, ...

Conce rt date: 2 1-M arch-20 08 p erfo rm er: Great B ig Sea un so ld Tickets : 1 0D , 22 H , 2 5A ,

2 5B, 25 C, 28 Z ,...

Sold Seats : 1 0A, 10 B, 10 C,

..., 22 N , 2 2P , ...

Conc ert date: 22 -M arch-2 00 8 perform er: Great Big Sea u ns oldT ickets: 35 A, 3 5B, 35 Cs oldT ickets: 10 A, 1 0B, ..., 34 Z ,

... 35D , ...

Type ofobject Attributevalues

Attributenames

Quick Quiz Solutions

Robot

currrentAvenue: 1

currentStreet: 0

direction: WESTbackpack: (em pty

Robot

currrentAvenue: 0

currentStreet: 0

direction: WESTbackpack: one

thing

Solutions may also containattributes for the label and color.

Two robots running a “relay.” 1.4: An Example Program (1/3)

Initial Situation Final Situation“B” picks up thebaton and takes itto “K”, whofinishes the race.

1.4: An Example Program (2/3)

// Set up the initial situation City beijing = new City();Robot ben = new Robot(beijing, 2, 0, Direction.SOUTH);Robot karel = new Robot(beijing, 2, 3, Direction.SOUTH);Thing baton = new Thing(beijing, 3, 0);Wall finishLine = new Wall(beijing, 3, 6, Direction.EAST);karel.setLabel(

"K"

);

ben.setLabel(

"B"

);

// Run the relay ben.move(); // bwbben.turnLeft();ben.pickThing();ben.move();ben.move();ben.move();ben.putThing();karel.move();karel.turnLeft();karel.pickThing();karel.move();karel.move();karel.move();karel.putThing();

1.4.5: Tracing a Program (1/2)

ben

karel

baton

Program Stmt

str

ave

dir

bp

str

ave

dir

bp

str

ave

2

0

S^

--^

2

3

S^

--^

3

0

ben.move();

3

0

S^

--^

2

3

S^

--^

3

0

ben.turnLeft();

3

0

E^

--^

2

3

S^

--^

3

0

ben.pickThing();

3

0

E^

ba

2

3

S^

--^

3

0

ben.move();

3

1

E^

ba

2

3

S^

--^

3

1

ben.move();

3

2

E^

ba

2

3

S^

--^

3

2

ben.move();

3

3

E^

ba

2

3

S^

--^

3

3

1.4.5: Tracing a Program (2/2)

ben

karel

baton

Program Stmt

str

ave

dir

bp

str

ave

dir

bp

str

ave

3

3

E^

ba

2

3

S^

--^

3

3

ben.putThing();

3

3

E^

--^

2

3

S^

--^

3

3

karel.move();

3

3

E^

--^

3

3

S^

--^

3

3

karel.turnLeft();

3

3

E^

--^

3

3

E^

--^

3

3

karel.pickThing();

3

3

E^

--^

3

3

E^

ba

3

3

karel.move();

3

3

E^

--^

3

4

E^

ba

3

4

karel.move(); etc.

3

3

E^

--^

3

5

E^

ba

3

5

1.5: Compiling and Executing Programs

Three kinds of errors: • 1.5.1: Compile-Time Errors Compile-Time Errors

•^

The compiler can’t translate your program into an executableform because your program doesn’t follow the language’s rules.

-^ Examples:

•^

karel.move;

instead of

karel.move();

-^ Public class RobotRelay

instead of

public class RobotRelay

-^ Unmatched braces; a

{^

without a corresponding

}

•^

Run-Time Errors

-^ Intent (Logic) Errors

Three kinds of errors: • 1.5.3: Intent (Logic) Errors Compile-Time Errors • Run-Time Errors • Intent (Logic) Errors

•^

The compiler can translate your program and it runs tocompletion, but it doesn’t do what you want it to.

-^ Example: In the relay race, the programmer forgets to instructkarel to turn left after picking up the baton. Initial Situation

Correct Final

Incorrect Final

Patterns are fragments of code that appear repeatedly.We give them names and learn them so that:1.7: Patterns

•^

we can recognize when they are being used

-^ we can discuss them easily with others -^ we can apply them in new situations When patterns are used in the text, an icon and the pattern nameappears in the margin. Discussed in detail later in the chapter.