| | Abstract class (in C++, pure virtual method): blueprint for a class without any implementation and thus cannot be instantiated |
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| | Abstract class methods: not all must be abstract, some can be concrete |
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| | Abstract class required: when at least one of the methods in the class is abstract |
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| | Abstract method: require non-abstract derived classes to provide their own implementation of this method |
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| | Interface class: an abstract class with public abstract methods all of which must be implemented in the inherited classes |
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| | Interface class methods: all must be abstract and public and thus accessibility modifiers not needed |
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| | Multiple interfaces: can be inherited |
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| | Namespace class: classes are declared inside a namespace |
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