Abstract Classes - Lecture Slides - Computer Science II | CS 162, Papers of Computer Science

Download Abstract Classes - Lecture Slides - Computer Science II | CS 162 and more Papers Computer Science in PDF only on Docsity! 1 1 CS162: Introduction to Computer Science II Abstract Classes 2 Abstract classes 3 Abstract Classes • An abstract class represents a generic concept eg. shape • An abstract class cannot be instantiated • Use the modifier abstract on the class header to declare a class as abstract, e.g.: public abstract class Shape{ // } 4 Abstract Classes • An abstract class often contains abstract methods with no definitions – The abstract modifier must be applied to each abstract method – Forces subclass to redefine the abstract method – An abstract class typically contains some non- abstract methods (with definitions) • A class declared as abstract is not required to contain abstract methods 5 Abstract Class Example public abstract class Shape { private String shapeName = ”undefined”; public abstract double area(); // no definition code public void setName(String name) { shapeName = name; } public String getName() { return shapeName; } } Note: You can’t instantiate a shape class because it is an abstract class! 6 Abstract Classes • A child of an abstract class must override the abstract methods of the parent – if you inherit from an abstract class but you don’t define the abstract functions, then the subclass must be abstract. • An abstract method cannot be defined as final (because it must be overridden) or static (because it has no definition yet)