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Which is the valid declarations within an interface definition?

Correct Answer: public double methoda();

Explanation:

Option A is correct. A public access modifier is acceptable. The method prototypes in an interface are all abstract by virtue of their declaration, and should not be declared abstract.


Option B is wrong. The final modifier means that this method cannot be constructed in a subclass. A final method cannot be abstract.


Option C is wrong. static is concerned with the class and not an instance.


Option D is wrong. protected is not permitted when declaring a method of an interface. See information below.


Member declarations in an interface disallow the use of some declaration modifiers; you cannot use transient, volatile, or synchronized in a member declaration in an interface. Also, you may not use the private and protected specifiers when declaring members of an interface.


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