Declaring an Abstract Class and Abstract Methods

You make a class abstract by declaring it with keyword abstract. An abstract class normally contains one or more abstract methods. An abstract method is one with keyword abstract in its declaration, as in

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public abstract void draw(); // abstract method

Abstract methods do not provide implementations. A class that contains any abstract methods must be explicitly declared abstract even if that class contains some concrete (nonabstract) methods. Each concrete subclass of an abstract superclass also must provide concrete implementations of each of the superclass’s abstract methods. Constructors and static methods cannot be declared abstract. Constructors are not inherited, so an abstract constructor could never be implemented. Though non-private static methods are inherited, they cannot be overridden. Since abstract methods are meant to be overridden so that they can process objects based on their types, it would not make sense to declare a static method as abstract.