213500 programmeren 1 6 september 2010 hoorcollege 2: interactie en condities 213500 programmeren 1...

213500 Programmeren 1

6 september 2010

HOORCOLLEGE 2: INTERACTIE EN CONDITIES

213500 PROGRAMMEREN 1

6 SEPTEMBER 2009

Software Systems - Programming 1

Programming

class diagrams and Java classes, parameters201300071-1B Module 2: Software Systems

15 November 2013

Week 1• Values, conditions• Classes, objects

Week 2• Specifications• Testing

Week 3• Abstraction,

inheritance

Week 4• Interfaces, abstract

classes• Arrays

Week 5• Collections• Generic structures

Week 6• Exceptions• Stream I/O• GUIs

Week 7• Concurrency• Networking

Week 8• Security

Week 9/10

Project


OVERVIEW PROGRAMMING LINE


PROGRAM DESIGN

A program must be designed before code is implemented

Example: Hotel Information System

System to store guests of a hotel, including the name and in which room they stay

(In general and sufficient for now) nouns indicate the relevant concepts, in this example:

Guest

Hotel

Room


PROGRAMMA ONTWERP

Ultimately program consists of objects that represent specific hotels, rooms and guests (instances of these concepts)

Examples

‘Hotel Fawlty Towers’

‘Room 101’, ‘Room 102’, etc.

‘Major Gowen’, ‘Miss Tibbs’, etc.

First generalise these objects by defining classes for them.

Hotel Room Guest

PROGRAM DESIGN

Define relations (associations) between the concepts (classes)

Hotel has Rooms Room belongs to a Hotel

Guest occupies a Room Room has (zero or one) Guest


one-to-one

one-to-many1..*

Hotel Room Guest0..11..*

PROGRAM DESIGN

Define attributes and features of each concept

Java terminology:

Attribute corresponds to field

Feature corresponds to method


HotelString nameString addresscheckin(String)

Roomint numberGuest getGuest()

GuestString nameRoom getRoom()

0..11..*

attributes

features

PROGRAM DESIGN

Define attributes and features of each concept


Hotel-String name-String address+checkin(String)

Room-int number+Guest getGuest()

Guest-String name+Room getRoom()

0..11..*

attributes

features

Visibility:-: private, can only be used by class itself+: public, can be used by every class

UML class diagrams:standard notation for classes, their

attributes and features and their relations


REMARKS

Program design is no complete system

Parts like the user interface are missing

Concepts, attributes and features are incomplete

Further development in phases

Design is no program

Gives a specifiation and structure

Not executable: details are missing

Next step: implement (in Java)

There may be more than one (good) design!

CLASSES AND INSTANCES

At runtime there are objects in the system

Class is a recipe for creating objects

Objects instances of a class


HotelString nameString addresscheckin(String)

Hotel h = new Hotel(“Fawlty Towers”, “Torquay”);

HotelString nameString address

Calls the constructor of the class.

“Fawlty Towers”“Torquay”

AttributesInstanceVariables


Strings are reference values

Variables store reference to String object


Hotelnameaddresscheckin(String)

HotelString nameString address

Stringvalueint length

“Fawlty Towers”13

Stringvalueint length

“Torquay”7


Example: Hotel 'Fawlty Towers', rooms 101 and 102 occupied by guest Major Gowen

HotelString nameString addressRoom room1Room room2

Roomint numberGuest guest

Roomint numberGuest guest

GuestnameRoom room

101

102null

“Fawlty Towers”

“Torquay”

“Majow Gowen”

Primitive values are stored in the variables.

Reference can be null (point to no object).


STATIC ATTRIBUTES

Values of static attributes stored in class variables


HotelString nameString addressdouble vat

checkin(String)

h1:HotelString nameString address

Static attributes are underlined

in UML.

Hoteldouble vat 0.06

h2:HotelString nameString address

ClassAttributes

ClassVariables

VARIABLES


class Hotel {

static double vat;

String name;

String address;

public double getBill(String guestName) {

Room room;

room = this.getRoom(guestName);

return room.getPrice() * (1 + Hotel.vat);

}

}

class variable:once per class

instance variables:once per object

local variables:once per method

execution

VARIABLES


class Hotel {

static double vat;

String name;

String address;

public double getBill(String guestName) {

Room room;

room = this.getRoom(guestName);

return room.getPrice() * (1 + Hotel.vat);

}

}this:

similar to local variable, refers toobject on which this method was called

formal parameter:similar to local

variable,value provided at

method call

Hotel h = ...h.getBill(“Major Gowen”);

Calls a method on object h and passes argument“Major Gowen”.


NAMING

In general

Identifiers consist of letters, digits and underscore “_”

Must start with letter

Conventions

Classes start with upper case letter (Guest)

Attributes / features start with lower case letter (name)

New word within identifier starts with upper case (getName)

Constants use all upper case and underscore to separate words (MAX_VALUE)

Use meaningful names no foo, var, i1, etc.

Cannot use keywords as identifiers

class, if, int, etc.


COMMENTS

Text for documenting the code

One-line: starts with // reaches till the end of the line

Multi-line: Between /* and */

Useful for programmer

Increases comprehensibility

Especially when working in a team

Improves maintainability

Is required in this course!


COMMENTS: JAVADOC

Special kind of comments for documenting how to use a class

Multi-line between /** and */

Start with textual description.

Use tags to document specific information

In front of

Class definition

important tags: @author

Method definition

important tags: @param, @return

Field definition


PACKAGES

Group related classes

Consists of identifiers separated by dots (use lower case letters)

Example: ss.week1.hotel

Must match folder hierarchy

Example: ss\week1\hotel\Guest.java

Package declaration in the first line of the file

package ss.week1.hotel;

Namespace: avoid name clashes between independently developed classes

Fully qualified class names include the containing package

Example: ss.week1.hotel.Guest

Details: section 2.8 in the book


JAVA FILES

package pname;

import <classes-from-other-packages>;

/** JavaDoc documentation of the class. */

public class CName {

/** JavaDoc documentation of the attribute. */

<field declarations>

/** JavaDoc documentation of the feature. */

<method declarations>

}

Details of import: section 2.9 of the book

For exampleJava packagesjava.util.Date;java.util.*;


DEFINITION OF A CLASS

package ss.week1.hotel;

/**

* Manages a hotel.

* @author John Cleese

* @version 2.0

*/

public class Hotel {

...

}

Javadoc-comment

namespace

Javadoc-tag for author of class

Visibility (for now only public for classes)

Javadoc-tag for class version

general description


DEFINITION OF AN ATTRIBUTE

/** * Stored the hotel’s name. */private String name;

/** * Constant representing a 1 star rating.

*/public static final String RATING_ONE_STAR = “*”;

Visibility (for now only public and private for attributes and features)

Field’s type

Class variable instead of instance variable

Value will not change during execution


DEFINITION OF A QUERY

/** * Returns the number of the room * occupied by the specified guest. * @param name the guest’s name * @return the room number */public int getRoomNumber(String name ) {

Room room = getRoom(name);

return room.getNumber();

}

Javadoc-tag for documenting the parameter “name”

formal parameter list, may be empty

result type

statement for returning the query result

Javadoc-tag for documenting the result value


DEFINITION OF A COMMAND

/**

* Finds a free room and

* occupies it with the guest.

* @param name the guest’s name

*/

public void checkin(String name) {

...

return;

}

No result value, therefore the result type is “void”.

Terminates the command without returning a value.


DEFINITION OF A CONSTRUCTOR

/**

* Creates a new Hotel.

* @param theName name of the hotel to create

* @param theAddress address of the hotel to create

*/

public Hotel(String theName, String theAddress ) {

this.name = theName;

this.address = theAddress;

}

Remarks

Constructor creates instances of the class and initialises the attributes

Name of the constructor is the same as the class name

Constructor has no result type

Classes represent concepts

Objects are instances of classes

Class diagrams can specify their attributes, features and relations

Class variables, instance variables, local variables, formal parameters

JavaDoc to document classes, attributes and features

Packages to group classes


MAIN POINTS

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