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Questions and Answers
What is the primary purpose of abstraction?
Which of the following is a characteristic of inner classes?
What is the term for creating objects from other objects?
What is the term for converting a superclass to its subclass?
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Which of the following is an example of abstraction?
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What is the purpose of encapsulation?
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What is the purpose of inheritance in object-oriented programming?
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What is the term for when multiple methods with the same name can be defined with different parameter lists?
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What is the primary goal of encapsulation in object-oriented programming?
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What is the purpose of an interface in object-oriented programming?
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What is the term for when a subclass provides a specific implementation for a method that is already defined in its superclass?
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What is the primary benefit of encapsulation in object-oriented programming?
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What is the term for showing only the necessary information to the outside world while hiding the implementation details?
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What is the keyword used to implement inheritance in Java?
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Study Notes
Inheritance
- Inheritance is a mechanism in which one class can inherit the properties and behavior of another class.
- The class that is being inherited from is called the superclass or parent class.
- The class that is doing the inheriting is called the subclass or child class.
- Inheritance is implemented using the
extendskeyword. - A subclass inherits all the fields and methods of its superclass.
- A subclass can also override the methods of its superclass.
Polymorphism
- Polymorphism is the ability of an object to take on multiple forms.
- There are two types of polymorphism:
- Method Overloading: When multiple methods with the same name can be defined with different parameter lists.
- Method Overriding: When a subclass provides a specific implementation for a method that is already defined in its superclass.
- Polymorphism is achieved through method overriding and method overloading.
Encapsulation
- Encapsulation is the concept of bundling data and methods that operate on that data within a single unit.
- In Java, encapsulation is achieved through the use of classes and objects.
- Data is hidden from the outside world and can only be accessed through methods provided by the class.
- Encapsulation helps to:
- Hide implementation details
- Improve data security
- Reduce coupling between objects
Interfaces
- An interface is a abstract class that defines a contract that must be implemented by any class that implements it.
- An interface defines a set of methods that must be implemented by any class that implements it.
- Interfaces are abstract and cannot be instantiated.
- Interfaces are used to define a common set of methods that can be called by other classes.
- Interfaces are implemented using the
implementskeyword.
Abstraction
- Abstraction is the concept of showing only the necessary information to the outside world while hiding the implementation details.
- Abstraction helps to:
- Reduce complexity
- Improve modularity
- Improve code reusability
- Abstraction is achieved through abstract classes and interfaces.
Inner Classes
- An inner class is a class that is defined inside another class.
- Inner classes have access to the members of the outer class.
- Inner classes can be used to implement helper classes or to encapsulate data and behavior.
- Inner classes can be static or non-static.
Composition
- Composition is the concept of creating objects from other objects.
- Composition is a "has-a" relationship between objects.
- Composition is used to create complex objects from simpler objects.
- Composition is achieved through the use of containers and component objects.
Downcasting and Upcasting
- Casting is the process of converting one object type to another.
- There are two types of casting:
- Upcasting: Converting a subclass to its superclass.
- Downcasting: Converting a superclass to its subclass.
- Upcasting is implicit and can be done without an explicit cast.
- Downcasting is explicit and requires an explicit cast.
- Downcasting can result in a
ClassCastExceptionif the object is not of the correct type.
Inheritance
- A class can inherit properties and behavior of another class using the
extendskeyword. - The inherited class is called the subclass or child class, while the class being inherited from is called the superclass or parent class.
- A subclass inherits all fields and methods of its superclass and can also override them.
Polymorphism
- Polymorphism is the ability of an object to take on multiple forms.
- There are two types of polymorphism: Method Overloading (multiple methods with the same name but different parameter lists) and Method Overriding (subclass provides a specific implementation for a method already defined in its superclass).
- Polymorphism is achieved through method overriding and method overloading.
Encapsulation
- Encapsulation is the concept of bundling data and methods that operate on that data within a single unit.
- In Java, encapsulation is achieved through the use of classes and objects.
- Data is hidden from the outside world and can only be accessed through methods provided by the class.
- Encapsulation helps to hide implementation details, improve data security, and reduce coupling between objects.
Interfaces
- An interface is an abstract class that defines a contract that must be implemented by any class that implements it.
- An interface defines a set of methods that must be implemented by any class that implements it.
- Interfaces are abstract and cannot be instantiated.
- Interfaces are used to define a common set of methods that can be called by other classes and are implemented using the
implementskeyword.
Abstraction
- Abstraction is the concept of showing only the necessary information to the outside world while hiding the implementation details.
- Abstraction helps to reduce complexity, improve modularity, and improve code reusability.
- Abstraction is achieved through abstract classes and interfaces.
Inner Classes
- An inner class is a class that is defined inside another class.
- Inner classes have access to the members of the outer class.
- Inner classes can be used to implement helper classes or to encapsulate data and behavior.
- Inner classes can be static or non-static.
Composition
- Composition is the concept of creating objects from other objects.
- Composition is a "has-a" relationship between objects.
- Composition is used to create complex objects from simpler objects and is achieved through the use of containers and component objects.
Downcasting and Upcasting
- Casting is the process of converting one object type to another.
- There are two types of casting: Upcasting (converting a subclass to its superclass) and Downcasting (converting a superclass to its subclass).
- Upcasting is implicit and can be done without an explicit cast.
- Downcasting is explicit and requires an explicit cast, and can result in a
ClassCastExceptionif the object is not of the correct type.
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Description
Understand the basics of object-oriented programming in Java, including inheritance and polymorphism.
