PDF Object-Oriented Programming Concepts

UNIT 5 – SL D1 1.1 Object – an abstract en;ty that describes the data that this en;ty has and the ac;ons that this en;ty can perform It can correspond to real-world en;;es, has helped in the evolu;on of good design prac;ces, and is a core aspect of OOP 1.2 Class – abstract ob...

UNIT 5 – SL D1 1.1 Object – an abstract en;ty that describes the data that this en;ty has and the ac;ons that this en;ty can perform It can correspond to real-world en;;es, has helped in the evolu;on of good design prac;ces, and is a core aspect of OOP 1.2 Class – abstract object en;;es Someone needs to build a specific object of a class before the object can be used Calling methods – sending messages to an object in order to perform ac;ons in OOP Every specific object cannot perform ac;ons but also has some specific data Every specific object has data that are specific to the object and accompany it throughout the execu;on of a program Classes, from which specific objects can be instan;ated, do not occupy any memory in a program Blueprints Classes do not occupy memory space in a program; a specific object that is instan;ated from the class occupies enough memory to accommodate the object’s data and ac;ons 1.3 Unifies modeling language (UML) – provides a way to visualize the design of any soVware system and has evolved into the standard for modeling object-oriented programs - Defines the number of different types of diagrams, but only the class diagram is within the scope of this book - Not the same as flow charts (UML diagrams) UML ac>vity diagram – considered as a modern extension of flow charts, and as such, UML can be thought of as a superset of flowcharts UML class diagram – the goal of this diagram is to depict the classes within an object-orientated program, as well as their collabora;ons - It illustrates classes as three-;er compartments, rectangles divided into 3 compartments  These ac;ons are presented in the returnType: ac>onName(inputType) form. inputType – type of data that is required by the specific ac;on returnType – a type of data that is returned by the specific ac;on aVer it has completed its execu;on - if it’s missing, that depicts an ac;on that does not return any data  UML class diagrams depict classes but also display how those classes collaborate Classes within an object-oriented program are connected in various ways, and UML class diagrams represent those connec;ons à they describe the sta;c structure of the system Associa>on – a line connec;ng the two classes Since UML class diagrams can become quite complex as programs increase in size and incorporate more classes, informa;on can be a\ached to these associa;ons to make things easier Each associa;on has 2 roles, and each role has a direc;on The role does not have to be explicitly named à it’s given a name to make things clearer Associa;ons between classes also have mul;plici;es – these are placed at each end of an associa;on line and indicate the number of objects of one class linked to one object of the other class Inheritance - the mechanism that takes advantage of similari;es - Inheritance can be thought of as an is-a or is-is-like rela;onship In UML class diagrams, inheritance is displayed with hollow arrows UML class diagrams can also be created using just the names of the classes that par;cipate in the diagram UML class diagrams are created in this manner to focus on the associa;ons, roles, mul;plici;es, and inheritances that take part between the classes and not on the actual data or ac;ons that each of these classes may contain 1.6 Descrip;on of UML class diagram was used to depict how various objects associated with each other, as well as how some classes could inherit data and ac;ons from other classes that were termed generaliza;ons 4 rela;onships in UML diagrams: associa>on, dependency, aggrega>on, inheritance ASSOCIATION Simplest rela;onship between 2 or more objects One or two role labels may be presented to signify the type of associa;on that takes place between the two objects DEPENDENCY – “USES“ RELATIONSHIP This s. “““ignifies that one object is dependent on one or more objects in order to func;on The implementa;on of an object depends on one or more other objects This occurs when one class links to one or more classes Represented with the dashed arrow à the arrow leaves the object that depends on the object that the arrow points to This can be described as “a client uses a supplier“ AGGREGATION The aggrega;on rela;onship signifies that one object belongs to another object and no other There is a parent and a child object – the child object cannot belong to another parent object The lifecycles of the parent and the child object are independent Example – can be seen in the UML class diagram Aggrega;on is said to be “has“ a rela;onship A hollow diamond followed by a line represents the aggrega;on rela;onship INHERITANCE The inheritance rela;onship (a.k.a generaliza;on) signifies that one object (a.k.a child or subclass) is a specialized form of another object (a.k.a parent or superclass) “is a” rela;onship A hollow triangle followed by a line represents the inheritance rela;onships 1.7 Dependencies between objects are what the name suggests: when one object uses another object, the first object depends on the second since it cannot func;on without it Dependencies are direc;onal, in that an object can depend on another object, but the second object does not necessarily need to depend on the first object as well Ex. If object A depends on object B, it does not necessarily mean that B also depends on A Finding the solu;on using object-oriented programming involves dealing with a number of interdependent objects Dependencies decrease the ability of code reuse, as well as increase maintenance overheads 1.8 1.9 DATA TYPES Data types – allow programs to classify these data into different types – crucial as to the meaning of the data, as well as to how they can be stored and manipulated Common data types: integer numbers, real numbers, Booleans, and strings INTEGER NUMBERS Represents a finite subset of the mathema;cal integers Can include nega;ve values Depending on the hardware and programming language used, every integer is represented by a specific number of bits REAL NUMBERS Represents numbers that contain frac;onal values Computers represent the approxima;on of real numbers with a trade-off between range and precision Two primi;ve data types that can represent floa;ng point numbers: float and double Double has more precision and can represent larger numbers than float BOOLEANS Represent only two possible values, true/false STRINGS Represents a series of characters and is mainly used to display informa;on Ex. String s=2this is a string” – would build a new String object that could be used to display the informa;on between the quotes to the user 1.10 Parameter – the name of the informa;on that is used in a method, func;on or procedure Argument – the value that is passed into a method, func;on, or procedure