By: Md Rezaul Huda Reza UNIVERSITY of South Asia 2 Md Rezaul Huda Reza Examples of real-world...

UNIVERSITY OF SOUTH ASIACSE 617

VISUAL AND INTERNET PROGRAMMING

Lecture 11: Review for the final

By: Md Rezaul Huda [email protected]

UNIVERSITY of South Asia

2Md Rezaul Huda [email protected]

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OBJECTS. REAL WORLD EXAMPLES

Examples of real-world objects: your pet, your desk, your bicycle (car?)

What do these real-world objects share? Answer: two characteristics

StateBehaviour

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OBJECTS. STATES AND BEHAVIOURS

State example:ColourBreedHungry

BehaviourRunningWagging tail Eating

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CLASSES Definition: A class is a blueprint, or

prototype, that defines the variables and the methods common to all objects of a certain kind.

Example : Class Car

Variables: make, currentSpeed, colour, currentGear

Methods: brake, change gears,accelerate

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ENCAPSULATION A class encapsulates:

Fields (Instance variables) represent the data

Instance methods represent the behavior The program does not worry how the class works

internally What is special about a class: both

data and behavior are presented in one “unit”

The methods and variables that constitute a class are called members of the class

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CREATING CLASSES IN C# Class declaration

declares the name of the class along with other attributes

Class Body within curly braces { and } declarations for all fields (instance variables) and

static fields (class variables) and implementations for all instance methods

and static methods (class methods)

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CONSTRUCTORS These are also part of a class definition A constructor is a sort of class method used to

create new instances - objects of the defined by the class

They are defined and used (called) Example of using/calling a constructor:

Form f; f = new Form();

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class (type)Variable/field

constructor



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MORE ON CONSTRUCTORS

Same identifier (name) as the class name

Do not return a value Void is not included Overloading possibleDefault constructor (the “no-args” constructor)No arguments Example: Form() It is defined by default if no other constructors

are defined

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THE MEMBERS OF A TYPICAL CLASS At least one constructor (the default

one) Methods Fields (the data, sometimes called

member variables) Properties (accessed like fields, but

actually methods)

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class name

fields

methods



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REFERENCE TYPES AND VALUE TYPE

• Value types: int, short, double, bool….• Reference types : objects that store references to the

actual data, not the value– built-in reference types: • object• string

• To instantiate a reference object in C#, you have to use new keyword.

• In C# we create a reference and then point the reference at an object allocated the heap with the new keyword, like:Object myobj;myobj = new Object();

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MODIFIERS Appear in

method/ constructor headings variable declarations the declaration heading for classes and other

class members Indicates how it can be accessed Types of modifiers

Access (to do with visibility)Static

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ACCESS MODIFIERS (PROTECTIONLEVELS FOR CLASS MEMBERS) Class members and classes can have one of the

following protection levelspublic – accessible to everyone internal – accessible within the same

assembly/namespaceprivate – accessible only inside classprotected – accessible for descendants –later lecture

Default protection levelsClass members (fields, instance methods) – privateClasses– internal

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THE EFFECTS OF PUBLIC AND PRIVATE ACCESSIBILITY

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violateEncapsulationUnless properties

enforceencapsulation

provide services to clients – for example, otherclasses

support othermethods in theclass

public private

variables

methods



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IMPLEMENTING DATA ENCAPSULATION USING PROPERTIES

Use C# properties to provide access to data safelyFields(instance variables) should be declared

private, with public properties that allow safe access to them

Public properties allow clients to:Get (obtain the values of) private data

getter (accessor): controls formatting and retrieval of dataSet (assign values to) private data

setter (mutator): ensure that the new value is appropriate for the data member

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CALLING STATIC METHODS EXAMPLE

double aValue = 78.926;double result1, result2;result1 = Math.Floor(aValue); // result1 = 78result2 = Math.Sqrt(aValue); // result2 = 8.88403061678651MessageBox.Show (“aValue rounded to 2 decimal places” + Math.Round(aValue, 2));

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Call it through the class name, not an instanceEach call returns a value

Round is called through a class. Must be static

A Value rounded to 2 decimal places is 78.93

MessageBox class as a static method Show()



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THE MEMBERS OF A TYPICAL CLASS

At least one constructor Methods (functions in other languages) Fields (the data, sometimes called member

variables) Properties (accessed like fields, but actually

methods)

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class name

fields

methodsproperties



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RELATIONSHIP BETWEEN C# ELEMENTS

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WHAT IS A NAMESPACE? Namespaces provide scope for the

classes defined within a group -an “umbrella”

System: most important and frequently used namespace

Each namespace enclosed in curly braces—{ }

Can define your own namespace

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ENTITY-RELATIONSHIP (E-R) MODELING Notation uses three main constructs

Data entitiesRelationshipsAttributes

Entity-Relationship (E-R) DiagramA detailed, logical representation of the

entities, associations and data elements for an organization or business

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ENTITY-RELATIONSHIP (E-R) MODELING

Entity A person, place, object, event or concept in the

user environment about which the organization wishes to maintain data

Represented by a rectangle in E-R diagrams Examples

An object such as a house or a car, an event such as a house sale or a car service, or a concept such as a customer transaction or order

Attribute A named property or characteristic of an entity

that is of interest to an organization Examples:

CUSTOMER can have id, name, phone no, etc A SALE has id, amount, date, etc

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RELATIONSHIPS Relationship

Association indicates that an event has occurred or that there is a natural link between entity types

Relationships are always labeled with verb phrases

Examples: One Park Has many Animals Many animals have the same species Many children can take a test

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ERD KEYS Primary Key

Each entity type must have an attribute (or set of attributes) that distinguishes one instance from other instances of the same type

1. key that will not change its value2. A key that will never be null3. The key’s value must be unique for each

instance of an entity Foreign key

is an attribute that completes a relationship by identifying the parent entity

Every relationship in the model must be supported by a foreign key.

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ENTITIES FOR BEAUTIFUL WILD DB CW Entities (you should have at least the

following): Animal Species RescuePark Donation Test- Child

Other possible entities for more complete design Donator– to know who adopted an animal; TestQuestion – to store separate questions for a test TestAttempt – if you allow a child to take the test more than

once. Voucher – to know what adopters or children were given

vouchers. Country – to know where the rescue park is

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TABLES Relational databases views all data in the

form of tables For our example:

A table for each Entity Each column represents an attribute, e.g. the

Animal table has attributes ID, animalName, etc. Relationships between entities are represented by

values stored in columns of the corresponding tables, e.g. Species_ID is an attribute of both the Animal table and the Species table. This makes it easy to link an animal with its species.

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BEAUTIFUL WILD DB VERSION 3 One extended version (not complete)

You would have to adapt/ extend further to fit your solution Available on teachmat

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SQL When a user wants to get some information from

a database file, he can issue a query. SQL is a query language that allows user

to specify the conditions. The program will go through all the records in

the database file and select those records that satisfy the condition.(searching).

A database driven application involves an application (C #)a set of tables in the databaseRead/ write to/from the DB using SQL

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3 TYPES OF SQL COMMANDS

1. Data Definition Language (DDL) 2. Data Manipulation Language (DML) 3. Data Control Language (DCL)

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Programmers should know this one



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SELECT Syntax:

Examples: SELECT animalName, animalWeight FROM

AnimalSELECT * FROM Animal

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SELECT column_name(s)FROM table_name

SELECT * FROM table_name



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THE WHERE CLAUSE Syntax:

The WHERE clause is used to extract only those records that fulfill a specified criterion..

Examples: SELECT * FROM Animal

WHERE Gender=‘Male'

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SELECT column_name(s)FROM table_nameWHERE column_name operator value

Values are in single quotes



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BASIC STRUCTURE OF AN SQL QUERY

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GeneralStructure

SELECT, ALL / DISTINCT, *,AS, FROM, WHERE

Comparison IN, BETWEEN, LIKE "% _"

Grouping GROUP BY, HAVING,COUNT( ), SUM( ), AVG( ), MAX( ), MIN( )

Display Order ORDER BY, ASC / DESC

LogicalOperators

AND, OR, NOT

Output INTO TABLE / CURSORTO FILE [ADDITIVE], TO PRINTER, TO SCREEN

Union UNION



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ADO.NET Is the .NET technology for accessing

structured data ADO.NET (ActiveX Data Objects) consists of a

number of classes that manage data and access data sources

Uniform object oriented interface for different data sources relational data bases XML dataother data sources

XML-based and independent from any particular database product or storage format

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CORE ADO.NET OBJECTSDataReader

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Datastore

Adapter DataSet

1*

1*

populates

Command

uses

uses

DataConsumer

usesConnection

Data Provider Objects



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TWO-LAYER (CONNECTED) APPROACH

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Application Data Source

DataReader

SelectCommand

Rows

Insert/Update

/DeleteCommand

Connection



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PROGRAM PATTERN FOR DATA ACCESS

• Use the right one

• Declare and request connection to database

• Open connection• Execute SQL

commands• create SQL command• execute SQL command

• Release resources and close connection

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1. Use Namespace2. Declare connection3. Declare a command object 4. Open connection to database

Process result5. Execute SQL commands

6. Close connection



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TRY…CATCH…FINALLY BLOCKS

Code that may create a problem is placed in the try block

try {Behaviour} Code to deal with the problem (the exception handler) is

placed in catch blocks This is called a catch clause

catch {WhatToDoIfExeptionOccurs} Code to be executed whether an Exception is thrown or

not is placed in the finally block

finally {WhatToDoAtTheEnd}

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PROGRAM PATTERN FOR DATA ACCESS

• Namespace• Declare and request

connection to database

• Open connection• Execute SQL

commands• create SQL command• execute SQL command

• Release resources and close connection

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1. Use the right Namespace2. Declare connection3. Declare a command object try { 4. Open connection to database

Process result5. Execute SQL commands

Release Resources } catch ( Exception e) {

Handle exception } finally {6. Close connection }



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ERRORS Design errors – the program simply

doesn’t do what was intendedExample: a program is supposed to

square each value of a list, but in fact it doubles each value

Runtime errors are unplanned – they give rise to premature abortion of a program run. A runtime error often can be handled in a program

Compilation errors - before run-time



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COMPILATION ERRORS The compiler converts source code into

MSIL (MicroSoft Intermediate Language) which can be executed by the CLR (Common Language Runtime). In Visual Studio, we run the compiler by Building the application The compiler works by applying language rules It checks errors in syntax (grammar) It checks resources are present (so it will pick up a

missing needed using statement) It checks that types match Compilation of program source code is a totally

separate process from running a program. We sort out the compilation errors before we can run a program.



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ERRORS AT RUNTIME Code is compiled runtime errors trigger (raise) the

creation of an exception object some circumstances are beyond

programmer’s control You have assumed nothing unusual would

occur Unless provisions are made for

handling exceptions, your program may crash or produce erroneous results



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EXCEPTION-HANDLING TECHNIQUES Use if statements if you can

can be used to guard against common problems such as integer divide by zero

Use try{ } catch{ } for serious errors that occur infrequently



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FILTERING MULTIPLE EXCEPTIONS

You can include multiple catch clauses Should be placed from most specific to the

most generic If a generic catch is included, it should

always be placed last



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DEBUGGING Purpose: to correct those logic errors

that keep your application from running correctly

Visual studio: integrated debugging functions. stop at procedure locations, inspect memory and register values, change variables, observe message traffic, and get a close look at what your code

does.



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THE DEBUGGER The Debugger is not meant to handle

runtime Exceptions – it is meant to help you determine their source

Possible to insert “breakpoints”, so that program will stop at them and then variables etc can be examined to determine the cause of the problem



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DEBUG SYMBOLS vital for a successful debugging session

BreakpointsStepping Through CodeViewing State

help the debugger correlate instructions in your application back to file names and line numbers in your source code

stored in a program database file with a .pdb extension



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STEPPING THROUGH CODE Once you pause execution you have the

ability to step through code, in other words, execute code one line at a time.

3 methods:Step Into Step Over Step Out



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TESTING Purpose – to test that every part of a

program works correctly according to the program specification and to engender confidence in the correctness of the program

Objective – to show the presence of errors in a program. A non-trivial program is unlikely to be 100% error free.

Testing involves : the design of test data, execution of the program with the test data

and evaluation of the results obtained.



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TESTINGGenerally the rate of error detection is proportional to the number of errors still remaining in the software. Consequently the number of errors presents declines exponentially over time.

No. of errors

Time0

Testing often continues until it becomes uneconomic. Hence often bugs remain in software.



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UNIT VS SYSTEM TESTING Small programs comprising a single

class are usually tested all at once. Larger programs are tested class by

class, called unit testing, and then brought together to test the whole, called integration or system testing.



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TECHNIQUES Black box (functional): focuses on the

range inputs and outputs of the program ignoring the actual construction of the code.

White box (structural): tests each and every possible path through software according to the statements and logic of the code.

Reviews or walkthroughs: desk checking, ‘dry run’

Stepping through code with debugger



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BLACK BOX TESTING– refers to the technique of testing a

system with no knowledge of the internals of the system.

– Black Box testers do not have access to the source code, and are oblivious of the system architecture.

i attempts to find the following types of error

incorrect or missing functions interface errors errors in data structures performance errors initialization and termination errors



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EXAMPLESuppose a program must accept the price of an orange, the number of oranges requested and to generate the total cost.

The price of an orange will be less than £1.00

The number of oranges will be in the range 1 to 20 inclusive.

A suitable error message should be displayed if either input entry in invalid.



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WHITE BOX TESTING technique of testing a system with knowledge of the internals of the system. White Box testers have access to the source code and are aware of the

system architecture.



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UNIT TESTING The first unit testing software was called

SUnitDeveloped by Kent Beck (from Extreme

Programming fame) and Erich Gamma (one of the Gang of Four, from Design Patterns fame)

Used for testing SmallTalk code Test frameworks now exist for many

programming languages JUnit for Java, CppUnit for C++, NUnit

for .NET, many othersKnown collectively as xUnit



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ANY QUESTION ? ? ?



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THANK YOU

By: Md Rezaul Huda Reza UNIVERSITY of South Asia 2 Md Rezaul Huda Reza Examples of real-world...

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