An Introduction To Programming And Object Oriented Design Pdf
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In this session, we introduce you to some of the core concepts of 6.
- Object-Oriented Analysis and Design
- A Comprehensive Introduction to Object-Oriented Programming with Java
Object-Oriented Analysis and Design
Object-oriented programming OOP is a programming paradigm based on the concept of " objects ", which can contain data and code: data in the form of fields often known as attributes or properties , and code, in the form of procedures often known as methods.
A feature of objects is that an object's own procedures can access and often modify the data fields of itself objects have a notion of this or self. In OOP, computer programs are designed by making them out of objects that interact with one another. Object-oriented programming uses objects, but not all of the associated techniques and structures are supported directly in languages that claim to support OOP.
The features listed below are common among languages considered to be strongly class- and object-oriented or multi-paradigm with OOP support , with notable exceptions mentioned. Modular programming support provides the ability to group procedures into files and modules for organizational purposes. Modules are namespaced so identifiers in one module will not conflict with a procedure or variable sharing the same name in another file or module.
Languages that support object-oriented programming OOP typically use inheritance for code reuse and extensibility in the form of either classes or prototypes. Those that use classes support two main concepts:. Objects sometimes correspond to things found in the real world. For example, a graphics program may have objects such as "circle", "square", "menu".
An online shopping system might have objects such as "shopping cart", "customer", and "product". Each object is said to be an instance of a particular class for example, an object with its name field set to "Mary" might be an instance of class Employee. Procedures in object-oriented programming are known as methods ; variables are also known as fields , members, attributes, or properties. This leads to the following terms:. Objects are accessed somewhat like variables with complex internal structure, and in many languages are effectively pointers , serving as actual references to a single instance of said object in memory within a heap or stack.
They provide a layer of abstraction which can be used to separate internal from external code. External code can use an object by calling a specific instance method with a certain set of input parameters, read an instance variable, or write to an instance variable.
Objects are created by calling a special type of method in the class known as a constructor. A program may create many instances of the same class as it runs, which operate independently. This is an easy way for the same procedures to be used on different sets of data. Object-oriented programming that uses classes is sometimes called class-based programming , while prototype-based programming does not typically use classes.
As a result, significantly different yet analogous terminology is used to define the concepts of object and instance. In some languages classes and objects can be composed using other concepts like traits and mixins.
In class-based languages the classes are defined beforehand and the objects are instantiated based on the classes. If two objects apple and orange are instantiated from the class Fruit , they are inherently fruits and it is guaranteed that you may handle them in the same way; e.
In prototype-based languages the objects are the primary entities. No classes even exist. The prototype of an object is just another object to which the object is linked. Every object has one prototype link and only one. New objects can be created based on already existing objects chosen as their prototype.
You may call two different objects apple and orange a fruit, if the object fruit exists, and both apple and orange have fruit as their prototype. The idea of the fruit class doesn't exist explicitly, but as the equivalence class of the objects sharing the same prototype.
The attributes and methods of the prototype are delegated to all the objects of the equivalence class defined by this prototype. The attributes and methods owned individually by the object may not be shared by other objects of the same equivalence class; e.
Only single inheritance can be implemented through the prototype. It is the responsibility of the object, not any external code, to select the procedural code to execute in response to a method call, typically by looking up the method at run time in a table associated with the object.
This feature is known as dynamic dispatch , and distinguishes an object from an abstract data type or module , which has a fixed static implementation of the operations for all instances. If the call variability relies on more than the single type of the object on which it is called i. A method call is also known as message passing. It is conceptualized as a message the name of the method and its input parameters being passed to the object for dispatch.
Encapsulation is an object-oriented programming concept that binds together the data and functions that manipulate the data, and that keeps both safe from outside interference and misuse.
Data encapsulation led to the important OOP concept of data hiding. If a class does not allow calling code to access internal object data and permits access through methods only, this is a strong form of abstraction or information hiding known as encapsulation.
Some languages Java, for example let classes enforce access restrictions explicitly, for example denoting internal data with the private keyword and designating methods intended for use by code outside the class with the public keyword. Methods may also be designed public, private, or intermediate levels such as protected which allows access from the same class and its subclasses, but not objects of a different class. In other languages like Python this is enforced only by convention for example, private methods may have names that start with an underscore.
Encapsulation prevents external code from being concerned with the internal workings of an object. This facilitates code refactoring , for example allowing the author of the class to change how objects of that class represent their data internally without changing any external code as long as "public" method calls work the same way.
It also encourages programmers to put all the code that is concerned with a certain set of data in the same class, which organizes it for easy comprehension by other programmers. Encapsulation is a technique that encourages decoupling.
Objects can contain other objects in their instance variables; this is known as object composition. Object composition is used to represent "has-a" relationships: every employee has an address, so every Employee object has access to a place to store an Address object either directly embedded within itself, or at a separate location addressed via a pointer. Languages that support classes almost always support inheritance.
This allows classes to be arranged in a hierarchy that represents "is-a-type-of" relationships. For example, class Employee might inherit from class Person. All the data and methods available to the parent class also appear in the child class with the same names.
These will also be available in class Employee, which might add the variables "position" and "salary". This technique allows easy re-use of the same procedures and data definitions, in addition to potentially mirroring real-world relationships in an intuitive way. Rather than utilizing database tables and programming subroutines, the developer utilizes objects the user may be more familiar with: objects from their application domain. Subclasses can override the methods defined by superclasses.
Multiple inheritance is allowed in some languages, though this can make resolving overrides complicated. Some languages have special support for mixins , though in any language with multiple inheritance, a mixin is simply a class that does not represent an is-a-type-of relationship. Mixins are typically used to add the same methods to multiple classes.
Abstract classes cannot be instantiated into objects; they exist only for the purpose of inheritance into other "concrete" classes that can be instantiated. In Java, the final keyword can be used to prevent a class from being subclassed.
The doctrine of composition over inheritance advocates implementing has-a relationships using composition instead of inheritance. For example, instead of inheriting from class Person, class Employee could give each Employee object an internal Person object, which it then has the opportunity to hide from external code even if class Person has many public attributes or methods.
Some languages, like Go do not support inheritance at all. Delegation is another language feature that can be used as an alternative to inheritance.
Subtyping — a form of polymorphism — is when calling code can be agnostic as to which class in the supported hierarchy it is operating on — the parent class or one of its descendants. Meanwhile, the same operation name among objects in an inheritance hierarchy may behave differently. For example, objects of type Circle and Square are derived from a common class called Shape.
The Draw function for each type of Shape implements what is necessary to draw itself while calling code can remain indifferent to the particular type of Shape being drawn. This is another type of abstraction that simplifies code external to the class hierarchy and enables strong separation of concerns.
In languages that support open recursion , object methods can call other methods on the same object including themselves , typically using a special variable or keyword called this or self. This variable is late-bound ; it allows a method defined in one class to invoke another method that is defined later, in some subclass thereof.
Terminology invoking "objects" and "oriented" in the modern sense of object-oriented programming made its first appearance at MIT in the late s and early s. In the environment of the artificial intelligence group, as early as , "object" could refer to identified items LISP atoms with properties attributes ;   Alan Kay later cited a detailed understanding of LISP internals as a strong influence on his thinking in Alan Kay, .
Another early MIT example was Sketchpad created by Ivan Sutherland in —61; in the glossary of the technical report based on his dissertation about Sketchpad, Sutherland defined notions of "object" and "instance" with the class concept covered by "master" or "definition" , albeit specialized to graphical interaction. In , Kristen Nygaard initiated a project for a simulation language at the Norwegian Computing Center , based on his previous use of the Monte Carlo simulation and his work to conceptualise real-world systems.
Simula introduced important concepts that are today an essential part of object-oriented programming, such as class and object , inheritance, and dynamic binding. For programming security purposes a detection process was implemented so that through reference counts a last resort garbage collector deleted unused objects in the random-access memory RAM.
Simula was promoted by Dahl and Nygaard throughout and , leading to increasing use of the programming language in Sweden, Germany and the Soviet Union. In , the language became widely available through the Burroughs B computers , and was later also implemented on the URAL computer. In , Dahl and Nygaard wrote a Simula compiler. They settled for a generalised process concept with record class properties, and a second layer of prefixes. Through prefixing a process could reference its predecessor and have additional properties.
Simula thus introduced the class and subclass hierarchy, and the possibility of generating objects from these classes. By , the Association of Simula Users had members in 23 different countries. Early a Simula 67 compiler was released free of charge for the DECsystem mainframe family. The object-oriented Simula programming language was used mainly by researchers involved with physical modelling , such as models to study and improve the movement of ships and their content through cargo ports.
Smaltalk included a programming environment and was dynamically typed , and at first was interpreted , not compiled. Smalltalk became noted for its application of object orientation at the language-level and its graphical development environment.
Smalltalk went through various versions and interest in the language grew. In the s, Smalltalk influenced the Lisp community to incorporate object-based techniques that were introduced to developers via the Lisp machine. Experimentation with various extensions to Lisp such as LOOPS and Flavors introducing multiple inheritance and mixins eventually led to the Common Lisp Object System , which integrates functional programming and object-oriented programming and allows extension via a Meta-object protocol.
In the s, there were a few attempts to design processor architectures that included hardware support for objects in memory but these were not successful.
A Comprehensive Introduction to Object-Oriented Programming with Java
Object-oriented programming OOP is a programming paradigm based on the concept of " objects ", which can contain data and code: data in the form of fields often known as attributes or properties , and code, in the form of procedures often known as methods. A feature of objects is that an object's own procedures can access and often modify the data fields of itself objects have a notion of this or self. In OOP, computer programs are designed by making them out of objects that interact with one another. Object-oriented programming uses objects, but not all of the associated techniques and structures are supported directly in languages that claim to support OOP. The features listed below are common among languages considered to be strongly class- and object-oriented or multi-paradigm with OOP support , with notable exceptions mentioned. Modular programming support provides the ability to group procedures into files and modules for organizational purposes.
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Search this site. Advertisement Analysis Examples. Limitation Of Ratio Analysis. Process Analysis Essay Examples. Object Orientation OO The perspective that systems should be constructed from objects, which themselves may be aggregations of smaller objects.
It is of vital importance to learn the fundamental concepts of object orientation before starting to use object-oriented development environments. OOP promotes good design practices, code portability, and reuse-but it requires a shift in thinking to be fully understood. NET, or Java or a modeling language such as UML , and instead first take the time to learn what author Matt Weisfeld calls "the object-oriented thought process.