2.5 Object Oriented Languages (OCR A Level Computer Science) Flashcards

A constructor is a special method within a class that is automatically called when an object is created.

A constructor is a special method in a class that sets initial values of instance variables and prepares the object for use when it is instantiated.

A class acts as a blueprint that describes the properties and behaviours of objects.

False.

A constructor is called automatically when an object is instantiated, not manually after creation.

A constructor defines the initial values of instance variables and performs any necessary setup for the object when it is created.

To create an object called mushypeas of type ItemForSale with the name “mushy peas” and price £0.89, you write: mushypeas = new ItemForSale("mushy peas", 0.89).

A method is a function associated with a class or object that defines the behaviours and actions that objects can perform in object-oriented programming.

A function returns a value after performing a task, while a procedure performs a task but does not return a value.

Objects created from a class can use its methods by accessing them with the dot notation (for example, jumboJet.Takeoff()).

False.

Static methods are associated with the class itself and can be called without creating an instance; they do not operate on specific instance data.

An instance method is a method associated with an individual object, operating on its data and properties.

Private methods are used to hide internal implementation details and can only be accessed within the same class, which helps organize and manage code internally.

When a method does not specify the keyword public or private, its default value is set to public.

Changes to public methods may affect other parts of the codebase that depend on them, so they should be carefully designed and remain backward compatible whenever possible.

An attribute is a data member or property associated with an object or a class in object-oriented programming, used to define the state of an object.

Attributes define the state of an object and can have different values for different instances of the same class.

False.

Attributes can be of various data types, such as integers, strings, Booleans, or even other objects.

Attributes can have different access rights, controlling how they are accessed.

A private attribute can only be accessed by instances of the class it belongs to, not from outside the class.

A class usually has many different attributes to represent all aspects of its state, such as a person object having a name, age, and address.

False.

Attributes declared within methods are local variables, which cannot have access modifiers and are only accessible within the block or method where they are declared.

In object-oriented programming, inheritance is when a class acquires the properties and methods of another class, allowing code reuse and establishing an IS-A relationship.

The main benefit of inheritance is that it promotes code reuse by allowing derived classes to use existing code from a base class, improving organisation and maintainability.

Inheritance establishes an IS-A relationship between the base class and the derived class.

True.

A derived class can add its own attributes and methods as well as inherit from the base class.

A parent class (also known as a base or superclass) is a class that defines common properties and behaviours to be inherited by derived classes.

A child class (also called a derived or subclass) inherits attributes and methods from a base class and can add its own functionality.

The super keyword is used to refer to the superclass and access its members from the subclass.

Inheritance means that the office and house classes (derived classes) gain the attributes and methods of the building base class.

Encapsulation is the practice of grouping data (attributes) and methods (functions) within a class, restricting direct access to some of the object's components to improve security and organisation.

The main purpose of encapsulation is to secure data and prevent accidental modification or misuse by controlling access to attributes and methods through access modifiers.

Encapsulation helps to organise code by keeping related data and methods together within an object.

False.

Encapsulation hides private variables from external code; they can only be accessed or modified through public methods.

A class can use private variables to ensure that data can only be changed using public methods.

Encapsulation promotes code reusability by allowing the same object or class to be used in different parts of a program without rewriting code, because its internal details are hidden.

Abstraction in encapsulation reduces complexity by hiding implementation details, making objects easier to use and understand.

Encapsulation is achieved by declaring distance as private and providing a public method updateDistance() to modify its value.

In object-oriented programming, polymorphism is the concept that allows objects to take on different forms or behaviours, enabling code to be more flexible, reusable, and easier to maintain.

Polymorphism provides flexibility and reusability to code, making it easier to write, manage, and adapt programs.

Polymorphism allows objects to share the same name or behaviour, but work in different ways.

Method overloading is a feature of polymorphism that allows multiple methods with the same name to exist in a class, each with different implementations or parameters.

True.

The override keyword allows a subclass to provide a new implementation for a method defined in its parent class.

In method overriding, the child class provides its own implementation of a method defined in the parent class.

Polymorphism allows objects of different classes to be treated as members of a common superclass, making code more versatile and adaptable.

An array of type Vehicle can store both Car and Motorcycle objects due to polymorphism.