Book Image

Java Coding Problems - Second Edition

By : Anghel Leonard
Book Image

Java Coding Problems - Second Edition

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.

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Java Coding Problems - Second Edition
Anghel Leonard
Mar, 2024 | 798 pages
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Table of Contents (16 chapters)
Preface
Preface
Who this book is for
What this book covers
To get the most out of this book
Get in touch
1
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
2
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
3
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
4
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
5
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
6
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
7
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
8
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
9
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<String, T> 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
10
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
11
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
12
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
13
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
14
Other Books You May Enjoy
Other Books You May Enjoy
15
Index
Index

85. Getting the number of quarters between two dates

This is just another problem that requires us to have a deep grasp of the Java Date/Time API. This time, we talk about java.time.temporal.IsoFields, which was introduced in Problem 73. One of the ISO fields is QUARTER_YEARS, which is a temporal unit representing the concept of a quarter-year. So, having two LocalDate instances, we can write this:

public static long nrOfQuarters(
    LocalDate startDate, LocalDate endDate) {
  return IsoFields.QUARTER_YEARS.between(startDate, endDate);
}

Feel free to challenge yourself to provide a solution for java.util.Date/Calendar.

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