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520 Object-Oriented Programming Chapter 9 // method overriding getButton public Button getButton() {} { return elevatorButton; } // method overriding getDoor public Door getDoor() {} { return elevatorDoor; } } Using forward engineering provides a sound beginning for code implementation in any language. Thinking About Objects Section 11.10 returns to interactions and focuses on how objects generate and handle the messages passed in collaborations. In addition, we forward engineer more class diagrams to implement these interactions. Eventually, we present the Java code for our simulator in Appendix G, Appendix H and Appendix I. 9.24 (Optional) Discovering Design Patterns: IntroducingCreational, Structural and Behavioral Design Patterns Now that we have introduced object-oriented programming, we begin our deeper presentation of design patterns. In Section 1.17, we mentioned that the gang of four described 23 design patterns using three categories creational, structural and behavioral. In this and the remaining Discovering Design Patterns sections, we discuss the design patterns of each type and their importance, and we mention how each pattern relates to the Java material in the book. For example, several Java Swing components that we introduce in Chapters 12 and 13 use the Composite design pattern, so we introduce the Composite design pattern in Section 13.18. Figure 9.40 identifies the 18 gang-of-four design patterns discussed in this book. Figure 9.40 lists 18 of the most widely used patterns in the software-engineering industry. There are many popular patterns that have been documented since the gang-offour book these include the concurrent design patterns, which are especially helpful in the design of multithreaded systems. Section 15.13 discusses some of these patterns used in industry. Architectural patterns, as we discuss in Section 17.10, specify how subsystems interact with each other. Figure 9.41 specifies the concurrency patterns and architectural patterns that we discuss in this book. Section Creational design patterns Structural design patterns Behavioral design patterns 9.24 Singleton Proxy Memento State Fig. 9.4040 The 18 Gang-of-four design patterns discussed in Java How to Program Fig. 4/e (part 1 of 2). Copyright 1992 2002 by Deitel & Associates, Inc. All Rights Reserved. 7/7/01