Classes and Objects Flashcards

Questions and Answers

What is a broad definition of class and what does it do?

An abstract description of objects that defines an object as having data and behaviors. This class acts as a template for objects used in another class.

A class may describe...

a single object (correct)

no objects at all

a bunch of objects (correct)

What is a hollow class or main class?

Classes which are just simple programs, rather than object-oriented programs.

What is data in terms of classes?

Attributes or properties. Signup and view all the answers

What are behaviors in terms of classes?

Methods. Signup and view all the answers

What is an object?

An instance of a class which defines it. Signup and view all the answers

What is a constructor?

A piece of code that creates a new object of that class. Signup and view all the answers

What will happen if you don't write a constructor?

Java will define one for you behind the scenes. Signup and view all the answers

How do you reference an object's data?

objectReference.data Signup and view all the answers

How do you reference an object's method?

objectReference.method() Signup and view all the answers

What is a key attribute of an instance variable and an instance method?

Instance variables belong to a specific instance; Instance methods are invoked by an instance of the class. Signup and view all the answers

What is a key attribute of a class variable, constant, and method?

Class variables are shared by all instances of the class; Class methods are not tied to a specific instance; Class constants are final variables shared by all instances. Signup and view all the answers

If a class is like a cookie cutter, an object is like what?

A cookie. Signup and view all the answers

Where do objects come from?

They are created by other objects. Signup and view all the answers

Where does the first object come from?

The main method is not part of any object; it is executed to get things started. Signup and view all the answers

What does the static keyword mean?

It says that the main method belongs to the class itself, not to the objects of the class. Signup and view all the answers

What is an anonymous object?

An object which is created without explicitly assigning it to a variable. Signup and view all the answers

When will a class be given a default constructor?

If no constructors are explicitly defined in the class. Signup and view all the answers

Which operator is used to access a data field or invoke a method from an object?

The dot operator. Signup and view all the answers

What is object-oriented programming?

Based around objects rather than actions and data rather than logic. Signup and view all the answers

What properties must a constructor's name have?

Must match class name exactly and must include a set of parentheses. Signup and view all the answers

What is a constructor method responsible for?

Creating the object in memory and, in some cases, giving the instance variables their initial values. Signup and view all the answers

Can a constructor method take arguments?

True Signup and view all the answers

What are some rules constructor methods must follow?

Must be public Signup and view all the answers

What does the 'this' keyword do?

Lets the compiler know that you want to refer to the instance variable and not another variable with the same name. Signup and view all the answers

What can the default constructor do?

Initialize your instance variables to default values. Signup and view all the answers

Why should you always have a default constructor?

You may want to construct an object and set the instance variable values later. Signup and view all the answers

When do you make a blank default constructor?

When you don't have any code you want to put in a default constructor but you need one anyway. Signup and view all the answers

What are the 3 main rules of method overloading?

METHODS must have the same name Signup and view all the answers

How do you use UML notation?

Refer to diagrams that represent the structure of classes and their relationships. Signup and view all the answers

Study Notes

Classes and Objects Overview

A class serves as an abstract blueprint for creating objects, defining their data attributes and methods (behaviors).
A class can represent various instances, from a single object to multiple related objects.
Hollow classes contain simple programs without object-oriented features.

Key Components of Classes

Attributes (or properties) refer to the data associated with a class, defining its state.
Methods represent the behaviors or functions that class objects can perform.

Objects and Instances

An object is an instance of a class, encapsulating both data and behaviors as defined by the class.
Objects are created through a piece of code called a constructor, which initializes the object's state.

Constructors

If a constructor is not explicitly defined, Java automatically generates a default constructor.
Constructors must have the same name as the class and cannot have a return type, not even void.

Object References

The dot operator (.) is used to access an object's data fields and to invoke its methods.
Data fields are referenced with the format: objectReference.data, and methods with objectReference.method().

Instance vs Class Attributes

Instance variables are specific to individual object instances, while instance methods are invoked by each instance.
Class variables are shared across all instances, and class methods are not tied to any specific instance.

Program Structure

The main method initializes program execution but is not tied to any object; it belongs to the class itself.
Anonymous objects are instantiated without being assigned to a reference variable.

Default Constructors

A class is given a default constructor when no constructors are explicitly defined.
It can be blank when no initializations are required, but it's important for flexibility in object creation.

Method Overloading

Method overloading requires methods to have the same name but different parameter lists or return types.
The same name can be reused, enabling multiple methods to coexist with distinct functionalities.

Additional Concepts

The this keyword differentiates instance variables from local variables with the same name.
Understanding UML notation can aid in visualizing class structures and relationships.

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Description

Test your knowledge on the fundamental concepts of classes and objects in programming. These flashcards cover definitions, examples, and key characteristics that differentiate classes from simple programs. Perfect for anyone looking to strengthen their understanding of object-oriented programming.