Any class with an abstract method is automatically abstract itself, and must be declared as such.A class may be declared abstract even if it has no abstract methods.
Any class with an abstract method is automatically abstract itself, and must be declared as such.A class may be declared abstract even if it has no abstract methods.
任一类以一个抽象方法自动地是抽象的本身,且必须被声明，一个类可以被声明是抽象的既使它没有抽象方法。