14-07-2011, 10:29 AM
Presented By:
PANKAJ KUMAR DASH
[attachment=14427]
Computer Programming
The history of computer programming is a steady move away from machine-oriented views of programming towards concepts and metaphors that more closely reflect the way in which we ourselves understand the world
Programming progression…
Programming has progressed through:
machine code
assembly language
machine-independent programming languages
procedures & functions
objects
Machine language – Mark I
Machine Language
0000 1001 1100 0110 1010 1111 0101 1000
1010 1111 0101 1000 0000 1001 1100 0110
1100 0110 1010 1111 0101 1000 0000 1001
0101 1000 0000 1001 1100 0110 1010 1111
Assembly Language – PDP-11
Assembly Language – Macro-11
GCD: TST B BEQ SIMPLE MOV A, R5 SXT R4 DIV B, R4 MOV B, A MOV R5, B CALL GCD SIMPLE: RETURN
Assembly Language – Macro-11
GCD: TST B BEQ SIMPLE MOV A, R5 SXT R4 DIV B, R4 MOV B, A MOV R5, B CALL GCD SIMPLE: RETURN
Machine-Independent Programming Languages – Fortran
! This example program solves for roots of the quadratic equation,
! ax^2 +bx +c =0,for given values of a, b and c.
!
PROGRAM bisection
IMPLICIT NONE
INTEGER :: iteration
DOUBLE PRECISION :: CC, Er, xl, x0, x0_old, xr
! Set convergence criterion and guess for xl, xr.
CC = 1.d-4
xl = 8.d-1
xr = 11.d-1
! Bisection method.
Er =CC +1
iteration = 0
DO WHILE (Er > CC)
iteration = iteration + 1
! Compute x0 and the error.
x0_old = x0
x0 = (xl + xr) / 2.d0
Er = DABS((x0 - x0_old)/x0)*100.d0
WRITE (*,10) iteration, x0_old, x0, Er
10 FORMAT (1X,I4,3(2X,E10.4))
Procedures & Functions – Pascal
program ValueArg(output);
{Shows how to arrange for a procedure to have arguments.}
procedure PrintInitials(First, Last : char);
{Within this procedure, the names First and Last represent the argument values. We’ll call write to print them.}
begin
write(‘My initials are: ’);
write(First);
writeln(Last)
end; {PrintInitials}
begin
PrintInitials (‘D’, ‘C’); {Any two characters can be arguments.}
PrintInitials (‘Q’, ‘T’); {Like strings, characters are quoted.}
PrintInitials (‘&’, ‘#’)
end. {ValueArg}
Objects
(My examples will be from Java)
“Intrinsic Power” vs. “Effective Power”
This progression is not a matter of “intrinsic power”
Anything you can do with a minimally capable computer language, you can theoretically do with any other minimally capable computer language
But that is like saying a shovel is theoretically as capable as a tractor. In practice, using a shovel might make things very hard…
Objects
Classes and Objects
A class is a prototype for creating objects
When we write a program in an object-oriented language like Java, we define classes, which in turn are used to create objects
A class has a constructor for creating objects
A Simple Class, called “Time” (partial)
Definition of an “Object”
An object is a computational entity that:
Encapsulates some state
Is able to perform actions, or methods, on this state
Communicates with other objects via message passing
1) Encapsulates some state
Like a record in Pascal, it has a set of variables (of possibly different types) that describe an object’s state
These variables are sometimes called an object’s attributes (or fields, or instance variables, or datamembers, or …)
Pascal Example: Represent a Time
type TimeTYPE = record Hour: 1..23;
Minute: 0..59;
end;
var inToWork, outFromWork: TimeTYPE;
Java Example: Represent a Time
Objects
2) Is able to perform actions, or methods, on this state
More than a Pascal record!
An object can also include a group of procedures/functions that carry out actions
3) Communicates with other objects via message passing
Sends messages to objects, triggering methods in those objects
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Structure of a Class Definition
History of Object-Oriented Programming
Started out for simulation of complex man-machine systems, but was soon realized that it was suitable for all complex programming projects
SIMULA I (1962-65) and Simula 67 (1967) were the first two object-oriented languages
Developed at the Norwegian Computing Center, Oslo, Norway by Ole-Johan Dahl and Kristen Nygaard
Simula 67 introduced most of the key concepts of object-oriented programming: objects and classes, subclasses (“inheritance”), virtual procedures
The Ideas Spread
Alan Kay, Adele Goldberg and colleagues at Xerox PARC extend the ideas of Simula in developing Smalltalk (1970’s)
Kay coins the term “object oriented”
Smalltalk is first fully object oriented language
Grasps that this is a new programming paradigm
Integration of graphical user interfaces and interactive program execution
Bjarne Stroustrup develops C++ (1980’s)
Brings object oriented concepts into the C programming language
Other Object Oriented Languages
Eiffel (B. Meyer)
CLOS (D. Bobrow, G. Kiczales)
SELF (D. Ungar et al.)
Java (J. Gosling et al.)
BETA (B. Bruun-Kristensen, O. Lehrmann Madsen, B. Møller-Pedersen, K. Nygaard)
Other languages add object dialects, such as TurboPascal
REVIEW: Definition of an “Object”
An object is a computational entity that:
Encapsulates some state
Is able to perform actions, or methods, on this state
Communicates with other objects via message passing
Encapsulation
The main point is that by thinking of the system as composed of independent objects, we keep sub-parts really independent
They communicate only through well-defined message passing
Different groups of programmers can work on different parts of the project, just making sure they comply with an interface
It is possible to build larger systems with less effort
Advantages
Building the system as a group of interacting objects:
Allows extreme modularity between pieces of the system
May better match the way we (humans) think about the problem
Avoids recoding, increases code-reuse
But there’s more…
Classes can be arranged in a hierarchy
Subclasses inherit attributes and methods from their parent classes
This allows us to organize classes, and to avoid rewriting code – new classes extend old classes, with little extra work!
Allows for large, structured definitions
Example of Class Inheritance
Java Class Hierarchy
Java Class Hierarchy, another view
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
A Circle is-a Shape is-a Object
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
A Circle is-a Shape is-a Object
How Objects are Created
How Objects are Created
How Objects are Created
How Objects are Created
Three Common Uses for Polymorphism
Using Polymorphism in Arrays
Using Polymorphism for Method Arguments
Using Polymorphism for Method Return Type
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
2) Using Polymorphism for Method Arguments
We can create a procedure that has Shape as the type of its argument, then use it for objects of type Rectangle, Circle, and Triangle
2) Using Polymorphism for Method Arguments
Polymorphism give us a powerful way of writing code that can handle multiple types of objects, in a unified way
3) Using Polymorphism for Method Return Type
We can write general code, leaving the type of object to be decided at runtime
Java Convinced Me to Start Teaching Object-Oriented in Intro to CS
Java is Object-Oriented from the Ground Up
Java has the elegance that comes from being designed after other OO languages had been in use for many years
Java has strong type checking
Java handles its own memory allocation
Java’s syntax is “standard” (similar to C and C++)
Java is a good teaching language, but it (or something close) will also be seen by students in industry
Object-Oriented Programming in Industry
Large projects are routinely programmed using object-oriented languages nowadays
MS-Windows and applications in MS-Office – all developed using object-oriented languages
This is the world into which our students are graduating…
Conclusions
Object-oriented programming provides a superior way of organizing programming projects
It encourages a high degree of modularity in programming, making large projects easier to implement
It provides powerful techniques like inheritance and polymorphism to help organize and reuse code
Object-oriented languages like Java both provide a good environment for beginning students to learn programming, and match real-world developments in computer programming
PANKAJ KUMAR DASH
[attachment=14427]
Computer Programming
The history of computer programming is a steady move away from machine-oriented views of programming towards concepts and metaphors that more closely reflect the way in which we ourselves understand the world
Programming progression…
Programming has progressed through:
machine code
assembly language
machine-independent programming languages
procedures & functions
objects
Machine language – Mark I
Machine Language
0000 1001 1100 0110 1010 1111 0101 1000
1010 1111 0101 1000 0000 1001 1100 0110
1100 0110 1010 1111 0101 1000 0000 1001
0101 1000 0000 1001 1100 0110 1010 1111
Assembly Language – PDP-11
Assembly Language – Macro-11
GCD: TST B BEQ SIMPLE MOV A, R5 SXT R4 DIV B, R4 MOV B, A MOV R5, B CALL GCD SIMPLE: RETURN
Assembly Language – Macro-11
GCD: TST B BEQ SIMPLE MOV A, R5 SXT R4 DIV B, R4 MOV B, A MOV R5, B CALL GCD SIMPLE: RETURN
Machine-Independent Programming Languages – Fortran
! This example program solves for roots of the quadratic equation,
! ax^2 +bx +c =0,for given values of a, b and c.
!
PROGRAM bisection
IMPLICIT NONE
INTEGER :: iteration
DOUBLE PRECISION :: CC, Er, xl, x0, x0_old, xr
! Set convergence criterion and guess for xl, xr.
CC = 1.d-4
xl = 8.d-1
xr = 11.d-1
! Bisection method.
Er =CC +1
iteration = 0
DO WHILE (Er > CC)
iteration = iteration + 1
! Compute x0 and the error.
x0_old = x0
x0 = (xl + xr) / 2.d0
Er = DABS((x0 - x0_old)/x0)*100.d0
WRITE (*,10) iteration, x0_old, x0, Er
10 FORMAT (1X,I4,3(2X,E10.4))
Procedures & Functions – Pascal
program ValueArg(output);
{Shows how to arrange for a procedure to have arguments.}
procedure PrintInitials(First, Last : char);
{Within this procedure, the names First and Last represent the argument values. We’ll call write to print them.}
begin
write(‘My initials are: ’);
write(First);
writeln(Last)
end; {PrintInitials}
begin
PrintInitials (‘D’, ‘C’); {Any two characters can be arguments.}
PrintInitials (‘Q’, ‘T’); {Like strings, characters are quoted.}
PrintInitials (‘&’, ‘#’)
end. {ValueArg}
Objects
(My examples will be from Java)
“Intrinsic Power” vs. “Effective Power”
This progression is not a matter of “intrinsic power”
Anything you can do with a minimally capable computer language, you can theoretically do with any other minimally capable computer language
But that is like saying a shovel is theoretically as capable as a tractor. In practice, using a shovel might make things very hard…
Objects
Classes and Objects
A class is a prototype for creating objects
When we write a program in an object-oriented language like Java, we define classes, which in turn are used to create objects
A class has a constructor for creating objects
A Simple Class, called “Time” (partial)
Definition of an “Object”
An object is a computational entity that:
Encapsulates some state
Is able to perform actions, or methods, on this state
Communicates with other objects via message passing
1) Encapsulates some state
Like a record in Pascal, it has a set of variables (of possibly different types) that describe an object’s state
These variables are sometimes called an object’s attributes (or fields, or instance variables, or datamembers, or …)
Pascal Example: Represent a Time
type TimeTYPE = record Hour: 1..23;
Minute: 0..59;
end;
var inToWork, outFromWork: TimeTYPE;
Java Example: Represent a Time
Objects
2) Is able to perform actions, or methods, on this state
More than a Pascal record!
An object can also include a group of procedures/functions that carry out actions
3) Communicates with other objects via message passing
Sends messages to objects, triggering methods in those objects
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Example of Object Creation and Message Passing
Structure of a Class Definition
History of Object-Oriented Programming
Started out for simulation of complex man-machine systems, but was soon realized that it was suitable for all complex programming projects
SIMULA I (1962-65) and Simula 67 (1967) were the first two object-oriented languages
Developed at the Norwegian Computing Center, Oslo, Norway by Ole-Johan Dahl and Kristen Nygaard
Simula 67 introduced most of the key concepts of object-oriented programming: objects and classes, subclasses (“inheritance”), virtual procedures
The Ideas Spread
Alan Kay, Adele Goldberg and colleagues at Xerox PARC extend the ideas of Simula in developing Smalltalk (1970’s)
Kay coins the term “object oriented”
Smalltalk is first fully object oriented language
Grasps that this is a new programming paradigm
Integration of graphical user interfaces and interactive program execution
Bjarne Stroustrup develops C++ (1980’s)
Brings object oriented concepts into the C programming language
Other Object Oriented Languages
Eiffel (B. Meyer)
CLOS (D. Bobrow, G. Kiczales)
SELF (D. Ungar et al.)
Java (J. Gosling et al.)
BETA (B. Bruun-Kristensen, O. Lehrmann Madsen, B. Møller-Pedersen, K. Nygaard)
Other languages add object dialects, such as TurboPascal
REVIEW: Definition of an “Object”
An object is a computational entity that:
Encapsulates some state
Is able to perform actions, or methods, on this state
Communicates with other objects via message passing
Encapsulation
The main point is that by thinking of the system as composed of independent objects, we keep sub-parts really independent
They communicate only through well-defined message passing
Different groups of programmers can work on different parts of the project, just making sure they comply with an interface
It is possible to build larger systems with less effort
Advantages
Building the system as a group of interacting objects:
Allows extreme modularity between pieces of the system
May better match the way we (humans) think about the problem
Avoids recoding, increases code-reuse
But there’s more…
Classes can be arranged in a hierarchy
Subclasses inherit attributes and methods from their parent classes
This allows us to organize classes, and to avoid rewriting code – new classes extend old classes, with little extra work!
Allows for large, structured definitions
Example of Class Inheritance
Java Class Hierarchy
Java Class Hierarchy, another view
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
A Circle is-a Shape is-a Object
Polymorphism
An object has “multiple identities”, based on its class inheritance tree
It can be used in different ways
A Circle is-a Shape is-a Object
How Objects are Created
How Objects are Created
How Objects are Created
How Objects are Created
Three Common Uses for Polymorphism
Using Polymorphism in Arrays
Using Polymorphism for Method Arguments
Using Polymorphism for Method Return Type
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
1) Using Polymorphism in Arrays
We can declare an array to be filled with “Shape” objects, then put in Rectangles, Circles, or Triangles
2) Using Polymorphism for Method Arguments
We can create a procedure that has Shape as the type of its argument, then use it for objects of type Rectangle, Circle, and Triangle
2) Using Polymorphism for Method Arguments
Polymorphism give us a powerful way of writing code that can handle multiple types of objects, in a unified way
3) Using Polymorphism for Method Return Type
We can write general code, leaving the type of object to be decided at runtime
Java Convinced Me to Start Teaching Object-Oriented in Intro to CS
Java is Object-Oriented from the Ground Up
Java has the elegance that comes from being designed after other OO languages had been in use for many years
Java has strong type checking
Java handles its own memory allocation
Java’s syntax is “standard” (similar to C and C++)
Java is a good teaching language, but it (or something close) will also be seen by students in industry
Object-Oriented Programming in Industry
Large projects are routinely programmed using object-oriented languages nowadays
MS-Windows and applications in MS-Office – all developed using object-oriented languages
This is the world into which our students are graduating…
Conclusions
Object-oriented programming provides a superior way of organizing programming projects
It encourages a high degree of modularity in programming, making large projects easier to implement
It provides powerful techniques like inheritance and polymorphism to help organize and reuse code
Object-oriented languages like Java both provide a good environment for beginning students to learn programming, and match real-world developments in computer programming