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Unformatted text preview: Chapter XXI Interfaces, Abstract Classes and Polymorphism Chapter XXI Topics 21.1 Introduction 21.2 Classes and Interfaces 21.3 Implementing Interfaces 21.4 Implementing Multiple Interfaces 21.5 Using Fields in an Interface 21.6 Abstract Classes 21.7 Polymorphism 21.8 The Object Class and Polymorphism 21.9 Summary Chapter XXI Interfaces, Abstract Classes and Polymorphism 1093 21.1 Introduction This chapter will be a brief introduction on topics that are covered in considerable detail in a second computer science course. The topics in this chapter are particularly important for students taking the AP Examination. It is very likely some questions on the exam will pertain to the material in this chapter. The title of this chapter is probably intimidating. Words like interfaces , abstract classes and polymorphism are not part of the typical vocabulary used by high school students. So right now let us examine these words before you look at some Java program examples. Interface is used quite frequently in computer technology. Interface describes the manner of communication between two computer areas. For instance, a program input can be done in a GUI environment or a text environment. With a GUI (Graphics User Interface) the program user is provided with windows, radio buttons, check boxes, pulldown menus and other graphical features that are used to get input from the user. A text environment is less user-friendly and usually requires that users know the type of input or commands that are required. The Mac Os environment and the Windows PC environment is a graphics interface and the DOS command line is a text interface. In everyday, non-technical English, abstract is used for various purposes. You may hear that a painting is abstract. If such is the case, the painting will not resemble a photograph of some image. You may not even have a clue initially what the painting resembles. The opposite of abstract is concrete . Concrete items can be detected with one or more of our senses. Abstract items are not detectable with our senses. During Word War II the entire downtown area of the city of Rotterdam, in the Netherlands was destroyed. Today there stands an abstract sculpture in Rotterdam that resembles a man in agony. The statue has a large hole in the center. Strictly using your senses you will observe a metal sculpture of a man with angular exaggerated features and a large hole in the center. The sculpture is not an accurate depiction of a human being. It turns out that the sculpture represents Rotterdam in the agony of its wartime destruction. The large hole represents the utter destruction of its city center or downtown area. Polymorphism is not part of any teenage vocabulary. I doubt if it is part of anybody's vocabulary, if you do not include computer scientists who use Object Oriented Design. Strange as this word may seem, you are familiar with parts of the word. You know that polygon means many sides. In today's special affects movies you have also become aware of...
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This note was uploaded on 10/14/2010 for the course APSC AP taught by Professor Kurt during the Spring '98 term at Wooster.
- Spring '98