Class Definitions Flashcards
What is the main characteristic of object instances in a class?
Each object instance will have the same behaviour but different property values or ‘state’.
What are the three basic components of a class?
- Properties
- Constructors
- Methods
What is the process of creating an object from a class called?
Instantiation
Define the term ‘class’ in the context of object-oriented programming.
A class is the model or blueprint from which an object is created.
True or False: A class reserves memory space for data.
False
What are properties in a class?
Properties store data representing the object’s state.
What is the role of constructors in a class?
Constructors allow each object to be initialised when created.
What do methods implement in a class?
Methods implement the behaviour of the object.
Fill in the blank: An object is an instance of a _______.
[class]
List the properties of a TicketMachine class.
- Price
- Balance
- Total
What is an accessor method?
An accessor method returns information about the state of the object.
What is a mutator method?
A mutator method changes the state of the object by modifying its properties.
Describe the purpose of the ‘insertMoney’ method in a TicketMachine.
It updates the current balance by adding the amount of money inserted.
What is the default constructor?
A constructor with no parameters that Java automatically provides if none is defined.
What happens when a method is invoked?
The flow of control jumps to the method and executes its code.
What is the purpose of the ‘printTicket’ method?
It prints a ticket and updates the total collected while resetting the balance.
What check does the improved ‘insertMoney’ method perform?
It checks that the customer enters a positive amount of money.
What does the improved ‘printTicket’ method check before printing a ticket?
It checks that the balance is greater than or equal to the price.
What is instance data?
Instance data refers to the values of the properties that each instance of a class has.
Define formal parameters.
Formal parameters are the parameter names used inside a constructor or method.
Define actual parameters.
Actual parameters are the values supplied to a constructor or method.
What is the significance of the return type in a method?
The return type indicates what type of value the method will return to the caller.
What is the purpose of the ‘getPrice’ method?
It returns the price of a ticket.
What does the constructor of the TicketMachine class do?
It initializes the properties of the TicketMachine object.
What is the main method typically used for in an application class?
To initiate or start the execution of the solution using the objects provided.
Why is it better practice to explicitly initialize properties?
To ensure properties have a defined value rather than relying on default values.
What does the phrase ‘method control flow’ refer to?
The sequence of execution that occurs when a method is called.
What improvements were suggested for the TicketMachine class?
- Check for sufficient money
- Refund excess money
- Validate ticket price
- Allow cancellation of ticket purchase
- Track total money collected
- Provide a way to empty the machine
What does the improved constructor in the TicketMachine class check?
It checks that the ticket price is greater than or equal to zero.
What is a local variable?
A variable declared within a method with a scope limited to that method.
What does the refundBalance() method do?
It refunds the current balance and resets the balance to zero.
What are formal parameters?
Variables that exist only during the constructor or method call and are defined in the header.
Define properties (fields).
Variables declared outside methods that persist throughout the object’s lifetime and maintain its state.
What are local variables initialized by?
They must be initialized before use and are NOT initialized by default.
In the testScope method, what is the error related to localVar2?
localVar2’s scope is limited to the block of the if statement.
What does the statement ‘TicketMachine[] machines = new TicketMachine[3];’ create?
An array capable of storing 3 references to TicketMachine objects.
How do you create instances of TicketMachine and assign them to an array?
By using the new operator to create each instance and assigning it to an element in the array.
What do the elements of an array of objects represent?
References to the actual object instances.
Can arrays be used as class properties?
Yes, arrays can be used as class properties.
What is the role of a class in the context of objects?
A class represents a concept, while an object is the embodiment of that class.
What is the purpose of constructors in a class?
To initialize a new instance of an object.
What do accessor methods do?
They return information about an object’s state.
What do mutator methods do?
They change an object’s state.
Fill in the blank: An object provides a collection of ______ that we can tell it to perform.
[behaviors]
True or False: A class can be used to create multiple objects.
True
What must a software designer consider when using arrays and objects?
The organization of data and objects that makes sense for the situation.
