Object-Oriented Programming & UML Diagrams

• Object: abstract entity with data and actions, fundamental to OOP and mirrors real-world entities
• Class: blueprint for creating objects
• Objects of a class can only exist if someone builds them
• Calling Methods: messages to an object prompting actions
• Every object has specific data attached to it and accompanies it through execution
• Classes are blueprints that do not occupy memory
• An object instantiated from a class does occupy memory to accommodate data and actions
• Unified Modeling Language (UML) is for visualizing software design and is a standard for object-oriented programs
• UML Class Diagram: shows classes within an object-oriented program and their collaborations: classes as three-part rectangles

Vehicle Class Diagram Example

• The top part shows the class name
• The middle part lists data held by an object of this class
• The last part lists the actions an object can perform
• Actions are presented as returnType: actionName(inputType)
• inputType is the type of data needed for the action
• returnType is the data type the action returns after completing; missing return type means no data is returned

Actions Associated with the Vehicle Class

• goForward(int d): moves the vehicle 'd' meters forward
• goBackward(int d): moves the vehicle 'd' meter backward
• boolean: stopMoving(): stops the vehicle, returning true if successful, false otherwise
• turn(int r): turns the vehicle 'r' degrees
• boolean: soundHorn(): sounds the horn, returning true if successful, false otherwise
• changeGear(int g): changes the gear to 'g'

UML Class Diagrams

• Illustrate classes and their collaborations
• Classes in an object-oriented program connect in various ways
• UML class diagrams show these connections, illustrating the system's static structure
• Association: A line connecting two classes
• Associations between classes have multiplicities at each end, marking the number of objects in one class that are linked to another

Roles and Inheritance

• Each association has two roles, each with a direction; roles can be named for clarity
• UML class diagrams focus on associations, roles, multiplicities, and inheritances between classes
• Inheritance: mechanism to use similarities in data through an is-a relationship with the parent class
• Inheritance is shown with hollow arrows in UML class diagrams

Relationships in UML Diagrams

• Four relationships exist: association, dependency, aggregation, inheritance

Association

• Simplest relationship between two or more objects, potentially with role labels.

Dependency

• Signifies that one object requires one or more other objects to function
• Represented by a dashed arrow from the dependent object to the object it depends on
• Client uses a supplier is often used to describe this relationship

Aggregation

• Indicates one object belongs to another, but only one other
• There is a parent and child object, the child object cannot belong to a different parent
• The lifecycles of the parent and child objects are independent
• This can be also be described as “has“ a relationship
• A hollow diamond with a line represents this relationship

Inheritance

• Relationship signifies that a child class is a specialized form of a parent class
• This can be also be described as an “is a“ relationship
• A hollow triangle with a line represents this relationship

Dependencies

• When one object uses another, the first depends on the second to function
• Dependencies are directional: Object A can depend on Object B without Object B depending on Object A
• A solution in object-oriented programming deals with numerous interdependent objects
• Dependencies reduce code reuse and increase maintenance

Data Types

• Data types are used so programs can classify and the meaning of data, including how the data is stored and manipulated
• Common examples include integer numbers, real numbers, Booleans, and strings

Integer Numbers

• Represents a finite subset of numbers, including negatives if specified
• Integer use a specific number of bits on the hardware and language used

Real Numbers

• Numbers that contain fractional values
• Represents the approximation of numbers with a trade-off in range and precision
• Float and double are to two data type options to use for numbers
• Double has more precision and can represent larger numbers tahn float

Booleans

• Represents only two possible values, true/false

Strings

• Represents as series of characters used mainly to display information

Action Implementations

• Objects have data and actions, such as calling the start() action from the Engine class in the Vehicle example
• Actions (methods) may or may not have parameters
• Data is passed to and from actions parameters
• Terms for actions: procedure, sub-procedure, function, routine, method, subroutine, module, subprogram
• Actions contain instructions to perform a specific task
• In Java, methods represent subprograms, and the main program can pass variables to a method

Parameters vs. Arguments

• Parameter: name of data used in a method, function, or procedure
• Argument: the value passed into a method, function, or procedure