Java Object-Oriented Quiz

Questions and Answers

What is an object in Java?

An object is something that contains both state and behavior.

What is the difference between a class and an object?

Objects are instances of classes. The class is the general template, and the object is the specific version.

What does it mean to be a client of a class?

Being a client of a class means that we can use its methods and functionality without necessarily understanding how it works.

What is a constructor in Java?

A constructor allows us to create a new instance of a class, usually initializing instance variables. Signup and view all the answers

Which of the following is the correct code for the constructor in the Card class?

suit = cardSuit; value = cardValue; Signup and view all the answers

What is an instance method?

An instance method is a piece of code called on a specific instance of the class. It is called with a receiver object. Signup and view all the answers

Which of the following is correct code? I.

III only Signup and view all the answers

What is the difference between a getter method and an accessor method?

There is no difference. They refer to the same idea. Signup and view all the answers

Which of these is an example of calling a static method?

Math.abs(x) Signup and view all the answers

Double sum(int one, double two)

II Signup and view all the answers

Which variables are in scope at the point labeled // POINT A?

sum and count Signup and view all the answers

What is printed by the following program?

hi Signup and view all the answers

What is the this keyword?

The this keyword refers to the current instance of the class. Signup and view all the answers

What is the output of the following code snippet?

false Signup and view all the answers

What is the output of the following code snippet?

true Signup and view all the answers

How do you call the superconstructor from a subclass?

You call it by making a call with the word super in the subclass constructor. Signup and view all the answers

Which of the following is a false statement about the classes?

True Signup and view all the answers

Say you are trying to create a set of classes that represent tools. Which is the proper first line of each class?

public class Hammer extends Tool; public class Screwdriver extends Tool Signup and view all the answers

What is the definition of polymorphism?

Polymorphism lets a method do different things depending on the type of the object it is called on. Signup and view all the answers

What method must a class contain to implement the Comparable interface?

public int compareTo(T other) Signup and view all the answers

Study Notes

Objects and Classes

An object in Java is a combination of state (data) and behavior (methods).
Classes serve as templates or blueprints for creating objects, while objects represent specific instances of those classes.

Class Clients and Constructors

A class client utilizes the class's methods without needing to know the internal workings.
Constructors are special methods used to instantiate a class and initialize its properties when creating an object.

Instance Methods and Accessors

Instance methods operate on a specific instance of a class and are invoked on a particular object.
Getter methods and accessor methods are interchangeable terms, both referring to methods that retrieve values of object properties.

Static Methods and Calling Conventions

Example of a static method call: Math.abs(x), which computes the absolute value of x.
Method signatures may vary, as illustrated in function definitions like double sum(int one, double two).

Scope and the 'this' Keyword

At a specific code point labeled "// POINT A," only variables named sum and count exist in the current scope.
The this keyword refers to the current object instance, emphasizing the context of which object's methods or properties are being accessed.

Inheritance and Superconstructor

To invoke a constructor from a parent class within a subclass, use the super keyword in the subclass's constructor.
Inheritance implies that subclasses like SciFi and Fantasy do not inherit constructors directly from their parent class Movie.

Class Declaration and Polymorphism

Subclass examples include public class Hammer extends Tool and public class Screwdriver extends Tool, indicating the relationship with the parent Tool class.
Polymorphism enables methods to operate differently based on the object type they are applied to, allowing for dynamic behavior in programming.

Comparable Interface

To implement the Comparable interface, a class must define the method public int compareTo(T other), which facilitates object comparison.

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Description

Test your knowledge of Java's object-oriented principles with this quiz. Explore key concepts such as objects, classes, and client relationships within Java programming. Perfect for beginners to deepen their understanding of OOP.