Questions and Answers
What is an abstract class?
A class that guides the design of subclasses but cannot itself be instantiated as an object; specifies how the subclass must be implemented.
An abstract class can be instantiated as an object.
False
Will a program that catalogs the types of trees in a forest benefit from an abstract class?
False
A program that catalogs trees with a different size estimation for each species will benefit from an abstract class.
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A program that maintains a grocery list will benefit from an abstract class.
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What is a concrete class?
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What is an abstract method?
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If a subclass does not implement an abstract method, then the subclass must also be defined as abstract.
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An abstract class cannot be instantiated because it has missing methods.
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An abstract class can include both method signatures for abstract methods and complete code for non-abstract methods.
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UML uses italics to denote abstract classes.
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Abstract classes provide compile-time polymorphism.
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What is an interface?
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A class can implement multiple interfaces.
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What keyword is needed to create an interface?
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How do you implement an interface in a class?
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What is an abstract class?
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What do interfaces define?
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What is an abstract class's role regarding default variables?
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What does an interface provide?
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Study Notes
Abstract Classes
- An abstract class serves as a blueprint for subclasses, guiding their design but cannot be instantiated.
- Subclasses are required to implement the behaviors specified by the abstract class to become concrete classes.
- Abstract classes may include both abstract methods (without implementation) and concrete methods (with implementation).
- If a subclass does not implement all abstract methods, it must also be declared as abstract.
Characteristics of Abstract Classes
- Cannot create objects of abstract classes due to missing methods.
- Denoted in UML using italics to distinguish them from concrete classes.
- Facilitate runtime polymorphism, allowing for abstract method calls without knowing the concrete class implementing them.
Concrete Classes
- A concrete class is one that is fully implemented and can be instantiated as an object.
Abstract Methods
- An abstract method is a method defined in an abstract class that subclasses must implement to be concrete.
Interfaces
- An interface defines a set of methods that must be implemented by any implementing class.
- A class can implement multiple interfaces, enabling multiple inheritance of type.
- Use the keyword
interface
in the class definition to create an interface. - Interfaces provide default variables and static final fields without restricting subclass inheritance.
- Unlike abstract classes, interfaces do not provide any implementation code.
Use Cases for Abstract Classes and Interfaces
- Abstract classes are suitable when you want to provide default code and properties for subclasses.
- Interfaces are best used when you want to enforce certain behaviors across unrelated classes.
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Test your understanding of abstract classes in programming with these flashcards. This quiz focuses on key definitions and true/false questions that help clarify the concept of abstract classes and their role in object-oriented design. Perfect for anyone studying object-oriented programming concepts.