Preface

17

Design Pattern Categories

19

How to Learn

20

Pattern-Based Learning

20

Category-Based Learning

21

Quick and Dirty Learning

23

Ad-Hoc Learning

23

1 MVC

27

1.1 Case Study: Read, Process, Display, and Post

28

1.2 Passing Select Options

33

1.3 Distributing Application Logic

34

1.4 Related Patterns

34

1.5 Summary

35

2 Abstract Factory

39

2.1 Case Study: Log Analysis

40

2.2 Related Patterns

47

2.3 Summary

47

3 Builder

49

3.1 Case Study: Jobs for Text Files

49

3.2 When to Use

66

3.3 Privacy

66

3.4 Summary

67

4 Factory

69

4.1 Case Study: FI Documents for Parties

69

4.2 Advantages

75

4.3 Related Patterns

75

4.4 Summary

76

5 Lazy Initialization

77

5.1 Case Study: Logging Errors

77

5.2 Advantages

81

5.3 Related Patterns

81

5.4 Summary

82

6 Multiton

83

6.1 Case Study: Vendor Balance

84

6.2 When to Use

88

6.3 When to Avoid

88

6.4 State Modification

89

6.5 Summary

89

7 Prototype

91

7.1 Case Study: Item Clone

91

7.2 Changing Class Properties

95

7.3 Clone Operations

96

7.4 Related Patterns

96

7.5 Summary

97

8 Singleton

99

8.1 Case Study: Subcomponents

99

8.2 Advantages and Disadvantages

106

8.3 Related Patterns

106

8.4 Summary

106

9 Adapter

109

9.1 Case Study: Project Management Tools

109

9.2 Glue Code

118

9.3 Two-Way Adapters

118

9.4 Legacy Classes

122

9.5 Summary

122

10 Bridge

123

10.1 Case Study: Messaging Framework

123

10.2 Advantages

131

10.3 Summary

131

11 Composite

133

11.1 Recursive Programming: A Refresher

133

11.2 Case Study: HR Positions

137

11.3 Advantages

144

11.4 Disadvantages

144

11.5 When to Use

145

11.6 Related Patterns

145

11.7 Summary

146

12 Data Access Object

147

12.1 Case Study: Potential Customers

147

12.2 Redundant Code Prevention

152

12.3 Related Patterns

153

12.4 Summary

153

13 Decorator

155

13.1 Case Study: User Exit

155

13.2 Advantages and Challenges

161

13.3 Related Patterns

162

13.4 Summary

162

14 Façade

165

14.1 Case Study: Bonus Calculation

166

14.2 When and Where to Use

168

14.3 Related Patterns

170

14.4 Summary

170

15 Flyweight

171

15.1 Case Study: Negative Stock Forecast

171

15.2 Disadvantages

181

15.3 When to Use

181

15.4 Related Patterns

182

15.5 Summary

182

16 Property Container

185

16.1 Case Study: Enhancing an SAP Program

185

16.2 Static vs. Instance Containers

194

16.3 Sharing Variables

195

16.4 Variable Uniqueness

196

16.5 Related Patterns

196

16.6 Summary

198

17 Proxy

199

17.1 Case Study: Sensitive Salary Information

199

17.2 When to Use

206

17.3 Related Patterns

207

17.4 Summary

207

18 Chain of Responsibility

209

18.1 Case Study: Purchase Order Approver Determination

209

18.2 Risks

217

18.3 Related Patterns

217

18.4 Summary

218

19 Command

221

19.1 Case Study: SD Documents

221

19.2 When to Use or Avoid

229

19.3 Related Patterns

229

19.4 Summary

230

20 Mediator

231

20.1 Case Study: Stock Movement Simulation

232

20.2 When to Use

241

20.3 Disadvantages

241

20.4 Summary

241

21 Memento

243

21.1 Case Study: Budget Planning

243

21.2 Risks

252

21.3 Redo

253

21.4 Summary

254

22 Observer

255

22.1 Case Study: Target Sales Values

256

22.2 Advantages

261

22.3 Disadvantages

261

22.4 Multiple Subjects

262

22.5 Related Patterns

263

22.6 Summary

264

23 Servant

265

23.1 Case Study: Address Builder

266

23.2 Extensions

274

23.3 Related Patterns

275

23.4 Summary

275

24 State

277

24.1 Case Study: Authorization-Based Class Behavior

277

24.2 Advantages

283

24.3 Related Patterns

284

24.4 Summary

284

25 Strategy

285

25.1 Case Study: Sending Material Master Data

286

25.2 Advantages

291

25.3 Passing Data to the Strategy Object

291

25.4 Optional Strategies

293

25.5 Intermediate Abstract Classes

297

25.6 Related Patterns

302

25.7 Summary

302

26 Template Method

305

26.1 Case Study: Average Transaction Volume

306

26.2 When to Use

318

26.3 Advantages and Risks

319

26.4 Degree of Abstraction

320

26.5 The “Hollywood Principle”

320

26.6 Summary

321

27 Visitor

323

27.1 Case Study: Incoming Invoice Processing

323

27.2 When to Use

333

27.3 Related Patterns

334

27.4 Summary

335

Appendices

337

A Object-Oriented Programming

339

A.1 Object-Oriented ABAP Development Environment

339

A.2 Class

341

A.3 Superclass

343

A.4 Abstract Class

345

A.5 Interface

351

A.6 UML

355

A.7 Summary

359

B Subclass Determination

361

B.1 Hardcoding

361

B.2 Convention over Configuration

361

B.3 SAP Class Tables

363

B.4 Custom Table

368

C Principles

371

C.1 Object-Oriented Principles

371

C.2 Design Principles

373

C.3 Anti-Patterns

375

D The Author

383