Introduction in Java

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1 Introduction
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Sitting at your desk in front of your workstation, you stare into space, trying to figure out how to write a new program feature You know intuitively what must be done and what data and which objects come into play, but you have this underlying feeling that there is a more elegant and general way to write this program In fact, you probably don't write any code until you can build a picture in your mind of what code does and how the pieces of the code interact The more that you can picture this "organic whole" or gestalt, the more likely you are to feel comfortable that you have developed the best solution to the problem If you don't grasp this whole right away, you might stare out of the window for a long time, even though the basic solution to the problem is quite obvious In one sense, you feel that the more elegant solution will be more reusable and more maintainable However, even if you are likely to be the only programmer, you feel reassured once you have designed a solution that is relatively clean and doesn't expose too many internal inelegancies One of the main reasons that computer science researchers began to recognize design patterns was to satisfy this need for good, simple, and reusable solutions The term design pattern sounds a bit formal to the uninitiated and can be somewhat off-putting when you first encounter it But, in fact, a design pattern is just a convenient way of reusing object-oriented (OO) code between projects and between programmers The idea behind design patterns is simple: to catalog common interactions between objects that programmers have often found useful A common pattern cited in early literature on programming frameworks is Model-View-Controller (MVC) for Smalltalk [Krasner and Pope, 1988], which divides the user interface problem into three parts (see Figure 11): Figure 11 The Model-View-Controller framework
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Data Model, which contains the computational parts of the program View, which presents the user interface Controller, which interacts between the user and the view
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Each aspect of the problem is a separate object, and each has its own rules for managing its data Communication between the user, the graphical user interface (GUI), and the data should be carefully controlled; this separation of functions accomplishes that very nicely Three objects talking to each other using this restrained set of connections is an example of a powerful design pattern
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In other words, a design pattern describes how objects communicate without becoming entangled in each other's data models and methods Keeping this separation has always been an objective of good OO programming If you have been trying to keep objects minding their own business, you are probably already using some of the common design patterns It is interesting that the MVC pattern is used throughout Java 12 as part of the JFC, also known as Swing components More formal recognition of design patterns began in the early 1990s when Erich Gamma [1993] described patterns incorporated in the GUI application framework, ET++ Programmers began to meet and discuss these ideas The culmination of these discussions and a number of technical meetings was the publication of the seminal book, Design Patterns Elements of Reusable Software, by Gamma, Helm, Johnson, and Vlissides [1995] This book, commonly called the Gang of Four, or GoF, book, became an all-time bestseller and has had a powerful impact on those seeking to understand how to use design patterns It describes 23 common, generally useful patterns and comments on how and when you might apply them We will refer to this groundbreaking book as Design Patterns, throughout this book Since the publication of Design Patterns, several other useful books have been published One closely related book is The Design Patterns Small talk Companion [Alpert, Brown, and Woolf, 1998], which covers the same 23 patterns but from the Smalltalk point of view In this book, we refer to it as the Smalltalk Companion
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