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Questions and Answers
What keyword is used in Java to indicate that a class is inheriting from another class?
In which type of inheritance does a subclass inherit from another subclass?
What is the purpose of using inheritance in Java?
What is the impact of the 'protected' modifier on class attributes in inheritance?
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Which of these is an example of single inheritance?
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In the context of inheritance, what is an interface used for?
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Which type of inheritance allows multiple subclasses to inherit from a single superclass?
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What would happen if you set an attribute in the superclass to 'private'?
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What is the purpose of the final keyword in a class declaration?
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Which of the following accurately describes compile-time polymorphism?
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In Java, runtime polymorphism is primarily achieved through which mechanism?
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Which statement best explains the concept of inheritance in Java?
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What do you understand about multilevel inheritance?
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How is single inheritance characterized in Java?
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Which of the following is NOT a benefit of using interfaces in inheritance?
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What is a key feature of reusability in classes?
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What is hierarchical inheritance?
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Which type of inheritance involves a class inheriting the properties of another class, which in turn inherits from yet another class?
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What type of inheritance is demonstrated when a Dog class and a Cat class both inherit from the Animal class?
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How are interfaces related to inheritance in Java?
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What does reusability in classes imply?
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In Java, how is a subclass defined?
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Which of the following is NOT a type of inheritance in Java?
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What characterizes single inheritance in Java?
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Study Notes
Java Inheritance Syntax
- The "extends" keyword indicates that you are making a new class that derives from an existing class.
- The "extends" keyword increases the functionality of the class being extended.
Inheritance Concepts
- There are two main types of inheritance: subclass and superclass.
- A subclass inherits from a superclass.
- A superclass is the parent class that is being inherited from.
Example 1-3: Inheritance of Car class from Vehicle Class
- The Car class inherits from the Vehicle class using the "extends" keyword.
- The Car class has its own attributes and methods.
- The Car class can access the attribute "brand" which is a protected attribute in the Vehicle class.
- The Car class can call the "honk()" method inherited from the Vehicle class.
Why and When To Use Inheritance?
- Inheritance is useful for code reusability, allowing you to reuse attributes and methods from an existing class when creating a new class.
Java Inheritance (Subclass and Superclass)
- Inheritance is a mechanism in which a class inherits properties and behaviors from another class called the superclass or subclass.
- In Java, it is possible to inherit attributes and methods from one class to another.
Types of Inheritance in Java
- Single inheritance: When a class inherits from another class.
- Multilevel inheritance: When there is a chain of inheritance where one class inherits from another class which inherits from a third.
- Hierarchical inheritance: When two or more classes inherit from a single class.
Single Inheritance Example
- The Dog class inherits from the Animal class, demonstrating single inheritance.
Multilevel Inheritance Example
- The BabyDog class inherits from the Dog class which inherits from the Animal class, demonstrating multilevel inheritance.
Hierarchical Inheritance Example
- The Dog and Cat classes inherit from the Animal class, demonstrating hierarchical inheritance.
Terms Used In Inheritance
- Class: A group of objects that share common properties.
- Subclass/Child class: A class that inherits from another class.
- Superclass/Parent class: The class from which a subclass inherits.
The "final" Keyword
- If you don't want other classes to inherit from a class, use the "final" keyword.
- If you try to access a final class, Java will generate an error.
Example 1-4: Using the "final" Keyword
- The code example shows a class called "Vehicle" declared as "final" which means it cannot be inherited.
- The "Main" class attempts to inherit from the "Vehicle" class, which will result in an error because a final class cannot be extended.
Java Polymorphism
- Polymorphism means "many forms".
- It occurs when we have many classes that are related to each other by inheritance.
- With inheritance, the subclass inherits methods and attributes from the superclass.
- Polymorphism allows us to perform a single action in different ways.
Types of Java Polymorphism
- Compile-time Polymorphism (Overloading): When there are multiple functions with the same name but different parameters.
- Runtime Polymorphism (Overriding): When two or more classes are related through inheritance and a method is overridden.
Compile-time Polymorphism (Overloading)
- Overloading occurs when there are multiple functions with the same name but different parameters.
- Functions can be overloaded by changes in the number of arguments or by a change in the type of arguments.
Runtime Polymorphism (Overriding)
- Occurs when two or more classes are related through inheritance.
- An "IS-A" relationship must exist between classes.
- A method in the subclass must override a method from the superclass to achieve Runtime polymorphism.
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Description
Explore the fundamentals of inheritance in Java, focusing on the use of the 'extends' keyword, and the relationship between subclasses and superclasses. Understand the benefits of code reusability and how to implement inheritance in your code with practical examples.