Summarizing Keyword Combinations
The following table summarizes the various valid (yes) and invalid (no) keyword
Keyword Interface Abstract class Class Sealed class struct
Abstract no yes no no no
New yes* yes yes yes no†
override no yes yes yes no‡
private no yes yes yes yes
protected no yes yes yes no**
public no yes yes yes yes
sealed no yes yes yes no
virtual no yes yes no no
*An interface can extend another interface and introduce a new method with the same
†A struct implicitly derives from System.Object, which contains methods that the struct
‡A struct implicitly derives from System.Object, which contains no virtual methods.
**A struct is implicitly sealed and cannot be derived from.
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