Object-Oriented Programming (Cambridge (CIE) A Level Computer Science): Flashcards

False.

Each object created from a class has its own unique values for the attributes, so two Student objects can hold different names and dates of birth.

A Student class might contain the attributes name, dateOfBirth and gender.

A constructor is the method used to create the objects of a class, setting the initial values of the attributes.

The five attributes are the manufacturer, model, price, mileage and whether the car is preowned.

It would use a Boolean, because a car either is or is not preowned.

Accelerate, to make the car go faster, and honkHorn, to sound the horn.

When a class is written so that its attributes cannot be accessed from outside it, those attributes are declared as private.

CurrentSpeed and HorizontalPosition are set to 0, because a vehicle starts stationary at the origin, while ID, MaxSpeed and IncreaseAmount are passed in as parameters.

True.

Python has no separate attribute declaration, so the exam requires the declarations to be included as comments, for example #self.  MaxSpeed integer.

IncreaseAmount is the value added to the current speed each time the vehicle increases its speed.

An object is a representation of a real-world entity, such as a teacher, an aeroplane or a mobile phone.

A class is a blueprint that describes the properties and behaviours of objects, while an object is a specific instance created from that blueprint, with its own unique values for the properties.

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

Constructors typically define the initial values of the instance variables.

As well as setting initial values, a constructor performs any necessary setup to prepare the object for use.

A teacher, an aeroplane and a mobile phone could all be modelled as objects.

False.

Each object is a separate instance with its own unique values for the properties.

The four attributes are firstName, surname, dateOfBirth and hobbies.

In Java, an object is created from a class using the new keyword.

Two objects are instantiated, with the identifiers person1 and person2.

person1 is created with "Bob", "Jones", "06/10/1981" and "E Sports".

The   init   method acts as the constructor in Python.

True.

Each attribute is declared with the private access modifier, so it cannot be accessed directly from outside the class.

It uses the self keyword, for example self.firstName = firstName.

A method is a function associated with an object or class that defines the behaviour and actions the object can perform.

The two main types of method are a function and a procedure.

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

False.

A procedure performs a task but does not return a value, which is what distinguishes it from a function.

Because they are associated with objects rather than the class itself, these methods are called instance methods.

It uses dot notation, in the form Objectname.Methodname.

The statement is jumboJet.Takeoff().

The four methods are take off, land, bank left and bank right.

Each object holds a manufacturer, a model, a passenger capacity and a maximum speed.

Although the designs differ, every aircraft requires the same methods, such as take off and landing, so one class can define that shared behaviour.

A public method is accessible and can be invoked by any code within the same class or from any external class.

A private method is only accessible within the same class and cannot be invoked by external code or other classes.

False.

A private method can only be called from within its own class.

Changes to public methods may affect other parts of the codebase, so they should be carefully designed, documented and kept backward compatible wherever possible.

A private method has a localised impact, because it is only used internally within its own class.

When you want to provide other parts of the program with access to a particular functionality or behaviour of the object or class.

When it holds internal implementation details that should not be accessed or used by external code.

In Python, a method whose name begins with a single leading underscore is treated as private by convention.

No. Python has no explicit access modifier, so a method marked as private can still be accessed from outside the class, but other developers should treat it as private and avoid doing so.

It creates an object called jumboJet from the aircraft class, giving it a manufacturer of Boeing, a model of 747, a capacity of 416 and a speed of 547.

An attribute is a data member, or property, associated with an object or a class.

The attributes define the state of an object.

False.

Attributes can hold different values for different instances of the same class.

An attribute can be any data type, including integers, strings, Booleans or even other objects.

As well as a data type, attributes can be given different access rights.

Private access means it can only be accessed within the Car class, and the String data type means the value it holds must be text.

The manufacturer attribute holds the value "Ford".

In most cases a class has many different attributes, so a single-attribute class is unusual.

The five attributes are name, age, gender, occupation and isMarried.

isMarried is declared as a boolean and age is declared as an int.

In Python, attributes are defined using the self keyword, followed by the attribute name and its initial value.

True.

All five attributes are declared with the private access modifier.

Inheritance allows a class to inherit the properties and behaviours, that is the attributes and methods, of another class.

A derived class can inherit and use the existing code from the base class, which avoids duplicating code and improves organisation and maintainability.

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

A Car is a Vehicle, so the Car class inherits the properties and behaviours associated with being a vehicle.

The base class is also known as the parent class or the superclass.

The derived class is also known as the child class or the subclass.

The base class is the blueprint or template from which the derived class inherits, defining the common properties and behaviours shared among multiple derived classes.

False.

A derived class inherits the attributes and methods of the base class, but it can also add additional attributes and methods of its own.

The Car class adds IsInsured, which records whether the car is insured, and EngineCapacity, which records the size of the engine.

TurnEngineOn(), TurnEngineOff() and SteerLeft() are all methods a Vehicle base class might define.

The super keyword is used within a subclass to refer to the superclass and access its methods, attributes or constructors.

In Java, a derived class inherits from a base class using the keyword extends.

The parent class name is written in brackets after the child class name, for example class Car(Vehicle):.

So that the attributes belonging to the base class are initialised, before the derived class sets its own additional attributes.

VerticalPosition is initialised to 0, while VerticalChange and MaxHeight are set from the parameters passed in.

The ID, the maximum speed and the increase amount are passed up to the Vehicle constructor, because they belong to the parent class.

True.

The Helicopter class declares VerticalPosition, VerticalChange and MaxHeight as private, in the same way the parent class declares its own attributes.

Encapsulation is the practice of grouping data (attributes) and methods (functions) together within a class.

It controls access to the data using access modifiers such as public and private, so the data cannot be accidentally modified or misused.

It organises code by keeping related data and methods together, and it promotes code reusability, so the same class can be used in different parts of a program without rewriting it.

Encapsulation uses a concept called abstraction, which reduces complexity by hiding the implementation details of the object.

They can use the methods and classes without having to understand how they have been constructed internally.

False.

Private variables are only accessible within the class itself, and external code must interact with the class through its public methods.

A get method is used to retrieve the value of an object's private attribute, and is also known as a getter or accessor method.

A set method is used to set the value of an object's private instance variable, and is also known as a mutator method.

To provide controlled access to the internal state of an object without allowing direct modification.

To enforce conditions or validations before the attribute is updated, so that access is controlled.

oldnumber is left unchanged, because the method only updates the attribute when the new value is not less than zero.

Because attributes are declared private, external code must use the public get methods to read their values.

A get method takes no parameters and returns the attribute without overwriting it.

It must return the value held in the CurrentSpeed attribute, taking no parameters and making no change to it.

False.

A set method updates the attribute, while it is the get method that returns its value.

Polymorphism allows objects to take on different forms or behaviours, so different objects can share the same method name but work in different ways.

Polymorphism makes code more flexible and more reusable, which also makes it easier to maintain.

Objects can be treated as belonging to a common group even when they belong to different classes, so the code adapts more easily to change.

The override keyword is used to provide a new implementation for a method that is already defined in the parent class.

Both output "Engines Started!", because they inherit the same method from the base class.

"I am a Motorcycle!" is output, because the version in the object's own class overrides the Vehicle class method.

It allows an array of type Vehicle to store both Car and Motorcycle objects, rather than keeping them in separate data structures.

It still outputs "I am a Car!", because the version that runs depends on the object actually created, not the declared type.

Run-time polymorphism happens when a subclass overrides a method defined in a superclass, and the correct version is chosen at run-time rather than compile-time.

It is empty, acting only as a placeholder for the subclasses to override.

make_sound(myDog) outputs Woof and make_sound(myCat) outputs Meow.

False.

One make_sound() accepts an object of type Animal and calls the correct version of speak() for whichever subclass was passed to it.

In run-time polymorphism the method call is resolved based on the actual type of the object.

The @Override annotation is written above the method header.

It adds the vertical change to the vertical position, adds IncreaseAmount to the current speed, and adds the updated current speed to the horizontal position.

The vertical position cannot exceed the maximum height, and the current speed cannot exceed the maximum speed.

True.

An overriding method keeps the same header as the method it overrides, and IncreaseSpeed() has no parameters.