Object-Oriented Programming, unit: Abstract Classes and Interfaces. Core concepts, terminology, and worked-example cues a college student meets for this unit, building on prior units without repeating them. Front: a term, concept, or short problem cue. Back: the definition, explanation, or answer.
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- What is an abstract class?
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A class that cannot be instantiated directly and may contain unimplemented methods- What is an abstract method?
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A method declared without an implementation, requiring subclasses to define it- Why would a class be declared abstract?
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To define a common structure while forcing subclasses to provide specific behavior- What is an interface, in OOP?
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A contract defining method signatures that implementing classes must provide- What is the main difference between an abstract class and an interface?
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An abstract class can include shared implementation; an interface traditionally only declares method signatures- Can a class implement multiple interfaces?
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Yes, a class can implement any number of interfaces- Can a class extend multiple abstract classes (in most single-inheritance languages)?
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No, typically only one class can be extended, but multiple interfaces can be implemented- What is a default method in an interface?
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A method with a provided implementation that implementing classes may optionally override- What is a marker interface?
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An interface with no methods, used to tag a class with a particular property- Why use an interface instead of a concrete class as a type?
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It allows code to depend on behavior rather than a specific implementation, improving flexibility- What is programming to an interface, as a design principle?
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Writing code that depends on abstract behavior rather than concrete implementations- What happens if a class fails to implement all abstract methods of an interface?
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The class must itself be declared abstract, or a compile error occurs- What is an abstract class's constructor used for, even though it cannot be instantiated?
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Initializing shared state that subclasses inherit when they are instantiated- What is a pure virtual function, in C++?
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A virtual function declared with "= 0" and no implementation in the base class, forcing derived classes to override it.- In C++, what makes a class abstract?
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Containing at least one pure virtual function.
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