Object-Oriented Programming: Inheritance

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Questions and Answers

What is the accessibility level of a protected member in Java?

Accessible by classes in the same package and subclasses (correct)

Accessible only by subclasses

Accessible only by the class itself

Accessible by all classes in all packages

Which of the following is an example of a built-in Java package?

java.custom

myPackage

java.util (correct)

userDefinedPackage

What is the primary characteristic of a default member in Java?

Accessible by all subclasses regardless of the package

Accessible only by classes in the same package (correct)

Accessible only by the public classes

Accessible by the entire program

What must be done first to create a user-defined package in Java?

Create a directory with the package name Signup and view all the answers

What is the purpose of packages in Java?

To provide a way to encapsulate data and classes Signup and view all the answers

What is the output when the main method in class TestSuper3 is executed?

animal is created dog is created Signup and view all the answers

Which statement about dynamic method dispatch is true?

It enables polymorphism by treating subclasses uniformly through their superclasses. Signup and view all the answers

What happens if a class is declared as final?

It cannot be subclassed, preventing alteration of its implementation. Signup and view all the answers

What will the following line cause: 'SmartPhone obj2 = new Phone();'?

It will cause a compiler error. Signup and view all the answers

Which method can be called on the object 'obj' of type Phone that is actually a SmartPhone?

showTime() Signup and view all the answers

What is the term used for the class that is inherited from in inheritance?

Superclass Signup and view all the answers

Which keyword is used to establish inheritance in Java?

extends Signup and view all the answers

What is NOT true about constructors in inheritance?

Constructors are inherited from the superclass. Signup and view all the answers

Which relationship does inheritance promote between classes?

Is-a Signup and view all the answers

Which statement accurately describes single inheritance?

It is the most common type of inheritance. Signup and view all the answers

Which members of the superclass can a subclass access?

Non-private members only Signup and view all the answers

What is the role of the super() keyword in a subclass?

To invoke the superclass constructor Signup and view all the answers

What can subclasses do regarding superclass methods?

Subclasses can override existing methods. Signup and view all the answers

What type of inheritance is demonstrated in the example with classes Animal, Dog, and BabyDog?

Multilevel Inheritance Signup and view all the answers

Which of the following best describes hierarchical inheritance?

Multiple subclasses extending a single superclass. Signup and view all the answers

Why does Java not support multiple inheritance of classes?

To avoid ambiguity when members of multiple classes are inherited. Signup and view all the answers

In the example of the MyClass implementation, what feature allows it to inherit from multiple sources?

Interfaces Signup and view all the answers

What will be the output of the method call `d.eat();` in the TestInheritance2 class?

eating... Signup and view all the answers

Which type of inheritance is a combination of single, multilevel, and multiple inheritance?

Hybrid Inheritance Signup and view all the answers

Which method provides the functionality for the Dog class in the hierarchical inheritance example?

bark() Signup and view all the answers

In single inheritance, which statement is accurate?

A subclass can inherit from only one superclass. Signup and view all the answers

What will happen if a method declared as final is attempted to be overridden in a subclass?

The program will not compile at all. Signup and view all the answers

Why should the final keyword be used judiciously in Java?

Overusing it can limit code flexibility and extensibility. Signup and view all the answers

What characteristic defines an abstract class?

It cannot be instantiated and serves as a blueprint for subclasses. Signup and view all the answers

What is the convention for naming final variables in Java?

They should be written in uppercase. Signup and view all the answers

In the provided example, what does the childClass inherit from finalclass?

The childClass cannot inherit anything from finalclass. Signup and view all the answers

What will be the output of the honda.run() method in the given example?

running safely with 100kmph Signup and view all the answers

What happens when you try to assign a new value to a final variable?

A compilation error will occur. Signup and view all the answers

Which of the following statements about abstract methods is correct?

Concrete subclasses must implement abstract methods. Signup and view all the answers

Study Notes

Inheritance

Inheritance is a fundamental OOP concept that allows creating new classes based on existing ones.
The extended class is called the subclass/child class, and the source class is called the superclass/parent class.
Inheritance promotes code reuse and supports the "is-a" relationship between classes.
Use the extends keyword in the class declaration to define inheritance.
Subclasses inherit all the fields and methods of the superclass (except private members).

Types of Inheritance

Single Inheritance: A subclass inherits from a single superclass. This is the most common type.
Multilevel Inheritance: A subclass acts as a superclass for another subclass, creating a chain of inheritance.
Hierarchical Inheritance: Multiple subclasses extend a single superclass.
Multiple Inheritance (through Interfaces): Java doesn't directly support multiple inheritance of classes, but allows it through interfaces. A class can implement multiple interfaces, inheriting their method signatures.
Hybrid Inheritance: A combination of different inheritance types, like single, multilevel, and multiple inheritance.

Dynamic Method Dispatch

Dynamic method dispatch is a mechanism that selects the appropriate method implementation at runtime, based on the object's actual type, not just the reference type.
Enables polymorphism, where objects of different subclasses can be treated uniformly through their common superclass.

The `final` Keyword

The final keyword restricts modification or inheritance of classes, methods, and variables.
Final Classes: Can't be subclassed. Ensures implementation remains unchanged.
Final Methods: Cannot be overridden by any subclass. Useful for enforcing specific method implementations in a hierarchy.
Final Variables: Value cannot be modified after assignment. Become constants (convention is to use all uppercase for variable names).

Abstract Classes and Methods

An abstract class cannot be instantiated directly. It serves as a blueprint for subclasses.
Declared using the abstract keyword.
Can contain abstract methods, which must be overridden by concrete subclasses.

Packages

Packages are a mechanism for organizing related classes and interfaces.
Provide data encapsulation and help reduce naming conflicts.
Two types: built-in and user-defined.
Built-in Packages: Part of the Java API, e.g., java.lang, java.io, java.util.
User-defined Packages: Created by the user. Specify package name by using package mypackage.

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Description

Explore the concept of inheritance in object-oriented programming, including types like single, multilevel, and hierarchical inheritance. Understand how subclasses and superclasses interact, and learn about the extends keyword for class declaration.