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Java Coding Problems - Second Edition

By : Anghel Leonard

4.5 (13)

Java Coding Problems

4.5 (13)

By: Anghel Leonard

Overview of this book

The super-fast evolution of the JDK between versions 12 and 21 has made the learning curve of modern Java steeper, and increased the time needed to learn it. This book will make your learning journey quicker and increase your willingness to try Java’s new features by explaining the correct practices and decisions related to complexity, performance, readability, and more. Java Coding Problems takes you through Java’s latest features but doesn’t always advocate the use of new solutions — instead, it focuses on revealing the trade-offs involved in deciding what the best solution is for a certain problem. There are more than two hundred brand new and carefully selected problems in this second edition, chosen to highlight and cover the core everyday challenges of a Java programmer. Apart from providing a comprehensive compendium of problem solutions based on real-world examples, this book will also give you the confidence to answer questions relating to matching particular streams and methods to various problems. By the end of this book you will have gained a strong understanding of Java’s new features and have the confidence to develop and choose the right solutions to your problems.

Preface

Preface

Who this book is for

What this book covers

To get the most out of this book

Get in touch

Text Blocks, Locales, Numbers, and Math

Text Blocks, Locales, Numbers, and Math

Problems

1. Creating a multiline SQL, JSON, and HTML string

2. Exemplifying the usage of text block delimiters

3. Working with indentation in text blocks

4. Removing incidental white spaces in text blocks

5. Using text blocks just for readability

6. Escaping quotes and line terminators in text blocks

7. Translating escape sequences programmatically

8. Formatting text blocks with variables/expressions

9. Adding comments in text blocks

10. Mixing ordinary string literals with text blocks

11. Mixing regular expression with text blocks

12. Checking if two text blocks are isomorphic

13. Concatenating strings versus StringBuilder

14. Converting int to String

15. Introducing string templates

16. Writing a custom template processor

17. Creating a Locale

18. Customizing localized date-time formats

19. Restoring Always-Strict Floating-Point semantics

20. Computing mathematical absolute value for int/long and result overflow

21. Computing the quotient of the arguments and result overflow

22. Computing the largest/smallest value that is less/greater than or equal to the algebraic quotient

23. Getting integral and fractional parts from a double

24. Testing if a double number is an integer

25. Hooking Java (un)signed integers in a nutshell

26. Returning the flooring/ceiling modulus

27. Collecting all prime factors of a given number

28. Computing the square root of a number using the Babylonian method

29. Rounding a float number to specified decimals

30. Clamping a value between min and max

31. Multiply two integers without using loops, multiplication, bitwise, division, and operators

32. Using TAU

33. Selecting a pseudo-random number generator

34. Filling a long array with pseudo-random numbers

35. Creating a stream of pseudo-random generators

36. Getting a legacy pseudo-random generator from new ones of JDK 17

37. Using pseudo-random generators in a thread-safe fashion (multithreaded environments)

Summary

Free Chapter

Objects, Immutability, Switch Expressions, and Pattern Matching

Objects, Immutability, Switch Expressions, and Pattern Matching

Problems

38. Explain and exemplifying UTF-8, UTF-16, and UTF-32

39. Checking a sub-range in the range from 0 to length

40. Returning an identity string

41. Hooking unnamed classes and instance main methods

42. Adding code snippets in Java API documentation

43. Invoking default methods from Proxy instances

44. Converting between bytes and hex-encoded strings

45. Exemplify the initialization-on-demand holder design pattern

46. Adding nested classes in anonymous classes

47. Exemplify erasure vs. overloading

48. Xlinting default constructors

49. Working with the receiver parameter

50. Implementing an immutable stack

51. Revealing a common mistake with Strings

52. Using the enhanced NullPointerException

53. Using yield in switch expressions

54. Tackling the case null clause in switch

55. Taking on the hard way to discover equals()

56. Hooking instanceof in a nutshell

57. Introducing pattern matching

58. Introducing type pattern matching for instanceof

59. Handling the scope of a binding variable in type patterns for instanceof

60. Rewriting equals() via type patterns for instanceof

61. Tackling type patterns for instanceof and generics

62. Tackling type patterns for instanceof and streams

63. Introducing type pattern matching for switch

64. Adding guarded pattern labels in switch

65. Dealing with pattern label dominance in switch

66. Dealing with completeness (type coverage) in pattern labels for switch

67. Understanding the unconditional patterns and nulls in switch expressions

Summary

Working with Date and Time

Working with Date and Time

Problems

68. Defining a day period

69. Converting between Date and YearMonth

70. Converting between int and YearMonth

71. Converting week/year to Date

72. Checking for a leap year

73. Calculating the quarter of a given date

74. Getting the first and last day of a quarter

75. Extracting the months from a given quarter

76. Computing pregnancy due date

77. Implementing a stopwatch

78. Extracting the count of milliseconds since midnight

79. Splitting a date-time range into equal intervals

80. Explaining the difference between Clock.systemUTC() and Clock.systemDefaultZone()

81. Displaying the names of the days of the week

82. Getting the first and last day of the year

83. Getting the first and last day of the week

84. Calculating the middle of the month

85. Getting the number of quarters between two dates

86. Converting Calendar to LocalDateTime

87. Getting the number of weeks between two dates

Summary

Records and Record Patterns

Records and Record Patterns

Problems

88. Declaring a Java record

89. Introducing the canonical and compact constructors for records

90. Adding more artifacts in a record

91. Iterating what we cannot have in a record

92. Defining multiple constructors in a record

93. Implementing interfaces in records

94. Understanding record serialization

95. Invoking the canonical constructor via reflection

96. Using records in streams

97. Introducing record patterns for instanceof

98. Introducing record patterns for switch

99. Tackling guarded record patterns

100. Using generic records in record patterns

101. Handling nulls in nested record patterns

102. Simplifying expressions via record patterns

103. Hooking unnamed patterns and variables

104. Tackling records in Spring Boot

105. Tackling records in JPA

106. Tackling records in jOOQ

Summary

Arrays, Collections, and Data Structures

Arrays, Collections, and Data Structures

Problems

107. Introducing parallel computations with arrays

108. Covering the Vector API’s structure and terminology

109. Summing two arrays via the Vector API

110. Summing two arrays unrolled via the Vector API

111. Benchmarking the Vector API

112. Applying the Vector API to compute FMA

113. Multiplying matrices via the Vector API

114. Hooking the image negative filter with the Vector API

115. Dissecting factory methods for collections

116. Getting a list from a stream

117. Handling map capacity

118. Tackling Sequenced Collections

119. Introducing the Rope data structure

120. Introducing the Skip List data structure

121. Introducing the K-D Tree data structure

122. Introducing the Zipper data structure

123. Introducing the Binomial Heap data structure

124. Introducing the Fibonacci Heap data structure

125. Introducing the Pairing Heap data structure

126. Introducing the Huffman Coding data structure

127. Introducing the Splay Tree data structure

128. Introducing the Interval Tree data structure

129. Introducing the Unrolled Linked List data structure

130. Implementing join algorithms

Summary

Java I/O: Context-Specific Deserialization Filters

Java I/O: Context-Specific Deserialization Filters

Problems

131. Serializing objects to byte arrays

132. Serializing objects to strings

133. Serializing objects to XML

134. Introducing JDK 9 deserialization filters

135. Implementing a custom pattern-based ObjectInputFilter

136. Implementing a custom class ObjectInputFilter

137. Implementing a custom method ObjectInputFilter

138. Implementing a custom lambda ObjectInputFilter

139. Avoiding StackOverflowError at deserialization

140. Avoiding DoS attacks at deserialization

141. Introducing JDK 17 easy filter creation

142. Tackling context-specific deserialization filters

143. Monitoring deserialization via JFR

Summary

Foreign (Function) Memory API

Foreign (Function) Memory API

Problems

144. Introducing Java Native Interface (JNI)

145. Introducing Java Native Access (JNA)

146. Introducing Java Native Runtime (JNR)

147. Motivating and introducing Project Panama

148. Introducing Panama’s architecture and terminology

149. Introducing Arena and MemorySegment

150. Allocating arrays into memory segments

151. Understanding addresses (pointers)

152. Introducing the sequence layout

153. Shaping C-like structs into memory segments

154. Shaping C-like unions into memory segments

155. Introducing PaddingLayout

156. Copying and slicing memory segments

157. Tackling the slicing allocator

158. Introducing the slice handle

159. Introducing layout flattening

160. Introducing layout reshaping

161. Introducing the layout spreader

162. Introducing the memory segment view VarHandle

163. Streaming memory segments

164. Tackling mapped memory segments

165. Introducing the Foreign Linker API

166. Calling the sumTwoInt() foreign function

167. Calling the modf() foreign function

168. Calling the strcat() foreign function

169. Calling the bsearch() foreign function

170. Introducing Jextract

171. Generating native binding for modf()

Summary

Sealed and Hidden Classes

Sealed and Hidden Classes

Problems

172. Creating an electrical panel (hierarchy of classes)

173. Closing the electrical panel before JDK 17

174. Introducing JDK 17 sealed classes

175. Introducing the permits clause

176. Closing the electrical panel after JDK 17

177. Combining sealed classes and records

178. Hooking sealed classes and instanceof

179. Hooking sealed classes in switch

180. Reinterpreting the Visitor pattern via sealed classes and type pattern matching for switch

181. Getting info about sealed classes (using reflection)

182. Listing the top three benefits of sealed classes

183. Briefly introducing hidden classes

184. Creating a hidden class

Summary

Functional Style Programming – Extending APIs

Functional Style Programming – Extending APIs

Problems

185. Working with mapMulti()

186. Streaming custom code to map

187. Exemplifying a method reference vs. a lamda

188. Hooking lambda laziness via Supplier/Consumer

189. Refactoring code to add lambda laziness

190. Writing a Function for parsing data

191. Composing predicates in a Stream’s filters

192. Filtering nested collections with Streams

193. Using BiPredicate

194. Building a dynamic predicate for a custom model

195. Building a dynamic predicate from a custom map of conditions

196. Logging in predicates

197. Extending Stream with containsAll() and containsAny()

198. Extending Stream with removeAll() and retainAll()

199. Introducing stream comparators

200. Sorting a map

201. Filtering a map

202. Creating a custom collector via Collector.of()

203. Throwing checked exceptions from lambdas

204. Implementing distinctBy() for the Stream API

205. Writing a custom collector that takes/skips a given number of elements

206. Implementing a Function that takes five (or any other arbitrary number of) arguments

207. Implementing a Consumer that takes five (or any other arbitrary number of) arguments

208. Partially applying a Function

Summary

Concurrency – Virtual Threads and Structured Concurrency

Concurrency – Virtual Threads and Structured Concurrency

Problems

209. Explaining concurrency vs. parallelism

210. Introducing structured concurrency

211. Introducing virtual threads

212. Using the ExecutorService for virtual threads

213. Explaining how virtual threads work

214. Hooking virtual threads and sync code

215. Exemplifying thread context switching

216. Introducing the ExecutorService invoke all/any for virtual threads – part 1

217. Introducing the ExecutorService invoke all/any for virtual threads – part 2

218. Hooking task state

219. Combining newVirtualThreadPerTaskExecutor() and streams

220. Introducing a scope object (StructuredTaskScope)

221. Introducing ShutdownOnSuccess

222. Introducing ShutdownOnFailure

223. Combining StructuredTaskScope and streams

224. Observing and monitoring virtual threads

Summary

Concurrency ‒ Virtual Threads and Structured Concurrency: Diving Deeper

Concurrency ‒ Virtual Threads and Structured Concurrency: Diving Deeper

Problems

225. Tackling continuations

226. Tracing virtual thread states and transitions

227. Extending StructuredTaskScope

228. Assembling StructuredTaskScope

229. Assembling StructuredTaskScope instances with timeout

230. Hooking ThreadLocal and virtual threads

231. Hooking ScopedValue and virtual threads

232. Using ScopedValue and executor services

233. Chaining and rebinding scoped values

234. Using ScopedValue and StructuredTaskScope

235. Using Semaphore instead of Executor

236. Avoiding pinning via locking

237. Solving the producer-consumer problem via virtual threads

238. Solving the producer-consumer problem via virtual threads (fixed via Semaphore)

239. Solving the producer-consumer problem via virtual threads (increase/decrease consumers)

240. Implementing an HTTP web server on top of virtual threads

241. Hooking CompletableFuture and virtual threads

242. Signaling virtual threads via wait() and notify()

Summary

Garbage Collectors and Dynamic CDS Archives

Garbage Collectors and Dynamic CDS Archives

Problems

243. Hooking the garbage collector goal

244. Handling the garbage collector stages

245. Covering some garbage collector terminology

246. Tracing the generational GC process

247. Choosing the correct garbage collector

248. Categorizing garbage collectors

249. Introducing G1

250. Tackling G1 throughput improvements

251. Tackling G1 latency improvements

252. Tackling G1 footprint improvements

253. Introducing ZGC

254. Monitoring garbage collectors

255. Logging garbage collectors

256. Tuning garbage collectors

257. Introducing Application Class Data Sharing (AppCDS, or Java’s Startup Booster)

Summary

Socket API and Simple Web Server

Socket API and Simple Web Server

Problems

258. Introducing socket basics

259. Introducing TCP server/client applications

260. Introducing the Java Socket API

261. Writing a blocking TCP server/client application

262. Writing a non-blocking TCP server/client application

263. Writing UDP server/client applications

264. Introducing multicasting

265. Exploring network interfaces

266. Writing a UDP multicast server/client application

267. Adding KEM to a TCP server/client application

268. Reimplementing the legacy Socket API

269. Quick overview of SWS

270. Exploring the SWS command-line tool

271. Introducing the com.sun.net.httpserver API

272. Adapting request/exchange

273. Complementing a conditional HttpHandler with another handler

274. Implementing SWS for an in-memory file system

275. Implementing SWS for a zip file system

276. Implementing SWS for a Java runtime directory

Summary

Other Books You May Enjoy

Other Books You May Enjoy

Index

Index

61. Tackling type patterns for instanceof and generics

Consider the following snippet of code that uses instanceof in the old-school fashion:

public static <K, V> void process(Map<K, ? extends V> map) {
  if (map instanceof EnumMap<?, ? extends V>) {
    EnumMap<?, ? extends V> books 
     = (EnumMap<?, ? extends V>) map;
    if (books.get(Status.DRAFT) instanceof Book) {
      Book book = (Book) books.get(Status.DRAFT);
      book.review();
    }
  }
}
// use case
EnumMap<Status, Book> books = new EnumMap<>(Status.class);
books.put(Status.DRAFT, new Book());
books.put(Status.READY, new Book());
process(books);

As we know from Problem 56, we can combine instanceof with generic types via unbounded wildcards, such as our EnumMap<?, ? extends V> (or EnumMap<?, ?>, but not EnumMap<K, ? extends V>, EnumMap<K, ?>, or EnumMap<K, V>).

This code can be written more concisely via the type pattern for instanceof as follows:

public static <K, V> void process(Map<K, ? extends V> map) {
  if (map instanceof EnumMap<?, ? extends V> books
    && books.get(Status.DRAFT) instanceof Book book) {
      book.review();
  }
}

In the example based on plain instanceof, we can also replace EnumMap<?, ? extends V> with Map<?, ? extends V>. But, as we know from Problem 53, this is not possible with type patterns because the expression type cannot be a subtype of pattern type (upcasting is allowed). However, this is not an issue anymore starting with JDK 21.

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