Java Encapsulation and Constructors Quiz

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Questions and Answers

What is the primary purpose of an accessor or getter method?

To return data from a private instance variable (correct)

To hide the implementation details of a class

To create an instance of a class (object)

To change the data of private instance variables

Which method name convention is used for setter methods?

set (correct)

get

define

In which case is a default constructor provided by Java?

When no constructors are defined at all (correct)

When the class has no instance variables

When the class is abstract

When explicit constructors are defined

What is constructor chaining?

Calling one constructor from another constructor Signup and view all the answers

What distinguishes an immutable class?

It remains unchanged after object creation Signup and view all the answers

What is a subclass in the context of inheritance?

A class that derives from another class Signup and view all the answers

What is the impact of encapsulation in object-oriented programming?

It enhances security by hiding data and methods Signup and view all the answers

Which of the following accurately describes constructor overloading?

Having different constructors with varying parameters Signup and view all the answers

What is a superclass in the context of object-oriented programming?

A class from which other classes are derived Signup and view all the answers

What makes encapsulation beneficial in object-oriented programming?

It allows writing of reusable programs. Signup and view all the answers

What must be the first statement of every constructor in Java?

A call to another constructor or super() Signup and view all the answers

What happens if a parent class does not have a no-argument constructor?

The compiler will throw an error if the child does not define constructors Signup and view all the answers

In Java, how does the compiler treat a child class constructor if no explicit call to a parent constructor is done?

The compiler will default to a no-argument super() call Signup and view all the answers

When is the parent constructor executed relative to the child constructor?

Before the child constructor Signup and view all the answers

Which of the following correctly describes encapsulation in Java?

It hides the internal state of an object by using private instance variables. Signup and view all the answers

What is the purpose of the 'this()' constructor call in Java?

To invoke another constructor of the same class Signup and view all the answers

What is method overriding in object-oriented programming?

Defining a new version of an existing method in a child class. Signup and view all the answers

What must be true about the method in the child class when overriding a parent class method?

It must have the same name and parameter list as the parent method. Signup and view all the answers

What does the constructor of the Person class output when an instance is created?

Person Signup and view all the answers

What is the result of calling new FirstYear() in the main method?

'Person' is printed followed by 'Student'. Signup and view all the answers

What is the purpose of the constructor in the Employee class?

To set the salary variable to a specific value. Signup and view all the answers

Which of the following statements about access modifiers is true regarding method overriding?

The child method must be at least as accessible as the parent method. Signup and view all the answers

What happens if the overridden method in the child class has a different return type?

It will cause a compile-time error. Signup and view all the answers

Which of the following describes the 'FirstYear' class in relation to inheritance?

It is a subclass of the Student class. Signup and view all the answers

Study Notes

Encapsulation

Encapsulation describes an object's ability to hide its data and methods.
Benefits of encapsulation:
- Encapsulation helps write reusable programs.
- Encapsulation restricts access to only public features of an object.
- Encapsulation is achieved by declaring instance variables as private and methods as public.

Accessor and Mutator Methods

Accessor or getter methods are public methods that return data from a private instance variable.
Mutator or setter methods are public methods that change the data stored in one or more private instance variables.

Constructors

A constructor is used in the creation of an object that is an instance of a class using the new keyword.
Constructors are never inherited.
Constructor declarations use the name of the class and have no return type.
Default Constructor: If you do not include any constructors in a class, Java provides a default constructor.
No-Argument Constructor: This is invisibly added to the class. It is also known as a no-argument constructor.
Constructor Overloading: Occurs when constructors have different types of parameters.
Constructor Chaining: When a constructor calls another constructor with a greater number of parameters.

Immutable Class

A class that remains unchanged after an object of another class is constructed.
To make a class immutable:
- Remove setter methods.
- Use the constructor to set values.

Inheritance

Inheritance allows a class to acquire all the attributes (fields) and behaviors (methods) of another class.
Subclass: A class derived from another class. It is also known as a derived class or child class.
Superclass: The class from which the subclass is derived. It is also known as a base class or parent class.

Rules in Defining Constructors

The first statement of every constructor is either a call to another constructor within the class using this() or a call to a constructor in the direct parent class using super().
The super() command may only be used as the first statement of the constructor.
If a super() call is not declared in a constructor, Java will insert a no-argument super() as the first statement of the constructor.
If the parent class does not have a no-argument constructor and the child class does not define any constructors, the compiler will throw an error. This is because the child class has an invisible no-argument super() that tries to call the constructor of the parent class.
If the parent class does not have a no-argument constructor, the compiler requires an explicit call to a parent constructor in each child constructor.

Calling Constructors and Overriding Methods

The parent constructor is always executed before the child constructor.
You can define a new version of an existing method in a child class that makes use of the definition in the parent class. This ability is called method overriding.
To override a method, declare a new method with the same name, parameter list, and return type as the method in the parent class.
The method in the subclass must be at least as accessible as the method in the parent class.

Calling Parent Class Constructor in the Child Constructor

Example code demonstrating constructor calling structure
The example code creates a class hierarchy: Person, Student, and FirstYear.
Parent class constructors are called before child class constructors.
The code demonstrates how the constructor of each class prints a message.

Example Code

The example code demonstrates how a child class can inherit from a parent class and override methods.
It also shows how a child class constructor can call the parent class constructor using the super() keyword.
The code creates an instance of the FirstYear class, which demonstrates the constructor chaining.

Key Facts and Concepts

Encapsulation and inheritance are fundamental concepts in object-oriented programming.
Constructors are essential for object initialization.
Overriding methods allows for polymorphism, where different classes can respond to the same method call in different ways.
The super keyword is crucial for calling parent class constructors and utilizing inherited functionality.
Understanding these concepts is essential for understanding object-oriented programming and its principles.

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Description

Test your knowledge on encapsulation and constructors in Java programming. This quiz covers the principles of data hiding, accessor and mutator methods, as well as the specifics of default and no-argument constructors. Get ready to enhance your understanding of object-oriented programming concepts!