U03 Flashcards: Class & Nested Classes

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Questions and Answers

The protected modifier cannot be applied to which of the following?

None of the others

Class-level variables (correct)

A method of a class (correct)

Object-level variables (correct)

Which of the following statements is not a reason for using nested classes?

It increases encapsulation.

It is a way of logically grouping classes that are only used in one place.

Nested classes can lead to more readable and maintainable code.

It supports a way for easily creating an object that is declared in an enclosing class declaration. (correct)

Select a correct statement about interfaces.

An interface is a class that has method implementations with no data.

In its most common form, an interface is a group of related methods with empty bodies. (correct)

An interface is a class that has at least one abstract method.

An interface is an abstract class with no data.

Select a correct statement.

None of the others. Signup and view all the answers

Which methods are applied in a class hierarchy?

Method overriding, method overloading. Signup and view all the answers

An abstract class must contain which of the following?

At least one abstract method. Signup and view all the answers

An interface can contain which of the following?

All of the other. Signup and view all the answers

To access data of a B object from a method of A, what must be done?

The B object must be referred by a reference declared in A. Signup and view all the answers

What is the best way to test whether x and y refer to the same constant?

if (x == y) Signup and view all the answers

Which of the following methods may appear in class Y, which extends X?

public void doSomething(int a, float b) {...} Signup and view all the answers

Which of the following restrictions apply to anonymous inner classes?

They may only read and write final variables of the enclosing class. Signup and view all the answers

Which of the following may override a method whose signature is void xyz(float f)?

public void xyz(float f) Signup and view all the answers

We can declare an object that belongs to which of the following?

All of the others. Signup and view all the answers

In a subclass, a calling to a constructor of superclass must be what?

The first line in a constructor of the subclass. Signup and view all the answers

What does the default modifier mean?

It provides access to any class in the same package. Signup and view all the answers

Which statement is correct about the protected modifier?

The protected modifier can only provide access to the members of the class itself. Signup and view all the answers

Study Notes

Class and Modifiers

The protected modifier cannot be applied to object-level variables, class-level variables, or methods of a class.
Access control in Java is defined by modifiers like private, protected, and default.

Nested Classes

Nesting classes can increase encapsulation and logically group related classes.
They can enhance readability and maintainability in code but may also introduce complexity.

Interfaces

An interface is a collection of related methods with empty bodies, allowing classes to implement multiple interfaces.
Interfaces do not have method implementations or data fields by default; they can only declare abstract methods.

Abstract Classes

An abstract class must contain at least one abstract method and can include concrete methods.
They can contain both abstract and concrete methods, despite common misconceptions about their limitations.

Method Overriding and Overloading

Method overriding allows a subclass to provide a specific implementation of a method declared in its superclass.
Method overloading lets a class have multiple methods with the same name but different parameters.

Constants and Interfaces

Interfaces can declare constants, which are immutable values accessible by all implementing classes.

Inner Classes

An inner class can access the enclosing class's members directly, provided it is instantiated properly within its context.

Enum Comparison

Comparing enum constants should be done using == for reference equality, which is more efficient than calling .equals().

Method Signatures

In extending classes, method signatures must match or adhere to overriding rules, such as visibility and return type.
Constructors in a subclass must call the superclass constructor as the first statement.

Access Modifiers

The default modifier makes a class member accessible only within the same package.
The protected modifier allows access from subclasses and classes in the same package but has specific rules on its usage.

Anonymous Inner Classes

Anonymous inner classes can access final or effectively final variables from the enclosing class but have restrictions regarding method access.

Abstract and Interface Objects

Objects can be declared belonging to an abstract class, an interface, or a subclass of a class that can be instantiated during runtime.

Java Constructor Rules

A constructor in a subclass must begin with a call to the superclass constructor using super(parameters).

General Java Principles

Understanding modifiers and their scopes is crucial for managing access and encapsulation in Java programming.

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Description

Test your knowledge of class definitions and the use of nested classes with these flashcards. Understand key concepts about class-level variables and the reasons for implementing nested classes in programming for better encapsulation and readability.