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Questions and Answers
Which of the following are access modifiers in C#?
Which of the following are access modifiers in C#?
Instance variables are also known as fields.
Instance variables are also known as fields.
True
What is an object in object-oriented programming?
What is an object in object-oriented programming?
An instantiation of a class.
What does the concept of information hiding emphasize in classes?
What does the concept of information hiding emphasize in classes?
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What is the default access level for members in a class when no modifier is explicitly specified?
What is the default access level for members in a class when no modifier is explicitly specified?
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Declaring a class directly creates actual objects.
Declaring a class directly creates actual objects.
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What are the two main steps involved in creating an object?
What are the two main steps involved in creating an object?
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Identifiers used for objects are references to their memory addresses.
Identifiers used for objects are references to their memory addresses.
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What is a constructor in object-oriented programming?
What is a constructor in object-oriented programming?
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C# automatically provides a default constructor even if you define your own constructor.
C# automatically provides a default constructor even if you define your own constructor.
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Overloading constructors allows multiple constructors with the same name but different parameter lists.
Overloading constructors allows multiple constructors with the same name but different parameter lists.
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How does C# choose the appropriate constructor when multiple constructors are available?
How does C# choose the appropriate constructor when multiple constructors are available?
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Instance methods have direct access to instance variables.
Instance methods have direct access to instance variables.
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What are methods that retrieve the data of fields called?
What are methods that retrieve the data of fields called?
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What are methods that modify the data of fields called?
What are methods that modify the data of fields called?
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Properties provide an alternative to using accessor and mutator methods.
Properties provide an alternative to using accessor and mutator methods.
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What are the keywords used in defining properties in C#?
What are the keywords used in defining properties in C#?
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A read-only property has both get and set accessors.
A read-only property has both get and set accessors.
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Auto-implemented properties require you to declare a backing field for the property.
Auto-implemented properties require you to declare a backing field for the property.
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Static data fields belong to a specific instance of a class.
Static data fields belong to a specific instance of a class.
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You can create private methods within a class.
You can create private methods within a class.
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What does the 'this' keyword refer to in a class?
What does the 'this' keyword refer to in a class?
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Which of the following operators can be overloaded in pairs in C#?
Which of the following operators can be overloaded in pairs in C#?
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What does overloading operators allow you to do with objects?
What does overloading operators allow you to do with objects?
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You can overload an operator for built-in data types in C#.
You can overload an operator for built-in data types in C#.
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What is the purpose of a destructor in object-oriented programming?
What is the purpose of a destructor in object-oriented programming?
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How are destructors identified in C#?
How are destructors identified in C#?
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You can declare arrays that hold elements of any type, including objects.
You can declare arrays that hold elements of any type, including objects.
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UML stands for Unified Modeling Language.
UML stands for Unified Modeling Language.
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What kind of diagrams are used within UML to visually represent systems?
What kind of diagrams are used within UML to visually represent systems?
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Study Notes
Programming for Computing Systems - Chapter 9
- Classes are the fundamental building blocks of object-oriented programming.
- Two categories of classes exist:
- Application programs with a
Main()method (typically declared as static). - Classes from which objects are instantiated. These can include a
Main()method, but it isn't standard.
- Application programs with a
- An object is an instance of a class.
- Instance variables (fields): data components of a class.
- State: the set of contents of an object's instance variables.
- Instance methods: methods associated with objects. Every instance of a class has the same methods.
- Class client/class user: a program or class that instantiates objects of another pre-written class (like
Console).
Creating a Class
- Class header/definition parts: include an optional access modifier and the
classkeyword, followed by a legal identifier for the class name. - Class access modifiers:
-
public -
protected -
internal -
private
-
Creating Instance Variables and Methods
- When creating a class, define both its fields (instance variables) and methods.
- Field access modifiers:
new,public,protected,internal,private,static,readonly, andvolatile. Most class fields arenonstaticandprivatefor security. - Using private fields within classes is information hiding.
- Most class methods are typically
public. This arrangement lets you control external access to data.- Private data is effectively manipulated by well-defined (programmer-defined) interfaces provided by public methods (e.g., accessing the gas level using a gauge).
Creating Objects
- Declaring a class doesn't create an object; it's just an abstraction (like a method until invoked).
- Two steps to create an object:
- Supply a type and identifier (e.g.,
Employee bob;). - Create the object, allocating memory (e.g.,
bob = new Employee();). - Identifiers for objects are references to their memory addresses.
- Supply a type and identifier (e.g.,
Understanding Constructors
- Constructor: a method that instantiates an object.
- Default constructor: automatically supplied if no programmer-defined constructors exist.
- Numerical fields are initialized to 0, character fields to '\0', booleans to
false, and references (strings and objects) tonull.
- Numerical fields are initialized to 0, character fields to '\0', booleans to
Overloading Constructors
- C# automatically provides a default constructor until a programmer-defined one is supplied.
- Constructors can be overloaded; multiple constructors with varying parameters are possible, as long as the argument lists don't cause ambiguity. The compiler chooses constructors based on their signatures.
Passing Parameters to Constructors
- You can create constructors that accept parameters.
Overloading Constructors(cont'd)
- Constructors can accept various parameter types.
Passing Objects to Methods
- You can pass objects as arguments to methods. This is similar to passing simple data types.
Accessor and Mutator Methods
- Fields in a class are often private due to data hiding.
- Accessor methods retrieve field data.
- Mutator methods modify field data.
- Each field requiring access by other classes needs both an accessor and a mutator.
Properties
- Properties provide an alternative to accessor and mutator methods.
- They modify and access private data members without using public methods.
Creating Properties
- Property: a class member that controls how fields are set and retrieved.
- Set accessors set object fields.
- Get accessors retrieve the stored values.
- Read-only property only has a get accessor.
Using Auto-Implemented Properties
- Auto-implemented properties are automatically generated with set and get accessors
- You don't need to explicitly define the backing field for auto-implemented properties.
More About Public and Private Access Modifiers
- Occasionally, public fields or private methods are needed, such as when all objects of a class need to access data.
- Static data fields belong to the class, not a specific instance.
UML Diagrams
- Unified Modeling Language (UML) diagrams are graphical representations for object-oriented systems. They have standard notations for depicting class structures and relationships.
Object Arrays
- Declare arrays to hold objects of a specific class.
Understanding Destructors
- A destructor, identified by a tilde (~), contains actions to be performed when an object is destroyed (e.g., memory release).
Class Layout Conventions
- Source code file layouts vary based on company/instructor guidelines. A typical organization lists fields first, then methods, with constructors often appearing near the top of the method section.
Using Operators in the Book Class
- Overload operators (+, -, etc.) to define how these operations work with objects. Creating custom behaviors for predefined operators. Operators can accept object types as arguments.
Summary
- Classes (with or without a
Mainmethod) define program structure and objects, which represent particular data instances of the classes. - Class fields and methods should be given considerations on whether to be
privateorpublic. - Object instantiation allocates memory; objects can have member properties passed to methods.
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Description
This quiz covers the basic concepts of object-oriented programming, focusing on classes and their components. It delves into the definitions, instance variables, methods, and the roles of class clients. Test your understanding of these foundational elements in programming.
