Modern Java Recipes. Simple Solutions to Difficult Problems in Java 8 and 9

321 Pages·2017·2.21 MB·English

by  Ken Kousen

Modern Java Recipes
Simple Solutions to Difficult Problems
in Java 8 and 9
Ken Kousen
Modern Java Recipes
by Ken Kousen
Copyright © 2017 Ken Kousen. All rights reserved.
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Table of Contents
Foreword. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . ix
Preface. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . xi
1. The Basics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
1.1 Lambda Expressions 2
1.2 Method References 6
1.3 Constructor References 10
1.4 Functional Interfaces 15
1.5 Default Methods in Interfaces 18
1.6 Static Methods in Interfaces 21
2. The java.util.function Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25
2.1 Consumers 26
2.2 Suppliers 28
2.3 Predicates 31
2.4 Functions 35
3. Streams. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39
3.1 Creating Streams 39
3.2 Boxed Streams 43
3.3 Reduction Operations Using Reduce 46
3.4 Check Sorting Using Reduce 55
3.5 Debugging Streams with peek 57
3.6 Converting Strings to Streams and Back 60
3.7 Counting Elements 63
3.8 Summary Statistics 65
3.9 Finding the First Element in a Stream 68
v
3.10 Using anyMatch, allMatch, and noneMatch 73
3.11 Stream flatMap Versus map 75
3.12 Concatenating Streams 79
3.13 Lazy Streams 83
4. Comparators and Collectors. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87
4.1 Sorting Using a Comparator 87
4.2 Converting a Stream into a Collection 91
4.3 Adding a Linear Collection to a Map 94
4.4 Sorting Maps 97
4.5 Partitioning and Grouping 100
4.6 Downstream Collectors 102
4.7 Finding Max and Min Values 104
4.8 Creating Immutable Collections 107
4.9 Implementing the Collector Interface 109
5. Issues with Streams, Lambdas, and Method References. . . . . . . . . . . . . . . . . . . . . . . . . 115
5.1 The java.util.Objects Class 115
5.2 Lambdas and Effectively Final 117
5.3 Streams of Random Numbers 120
5.4 Default Methods in Map 122
5.5 Default Method Conflict 127
5.6 Iterating Over Collections and Maps 130
5.7 Logging with a Supplier 132
5.8 Closure Composition 134
5.9 Using an Extracted Method for Exception Handling 138
5.10 Checked Exceptions and Lambdas 141
5.11 Using a Generic Exception Wrapper 144
6. The Optional Type. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 147
6.1 Creating an Optional 148
6.2 Retrieving Values from an Optional 150
6.3 Optional in Getters and Setters 154
6.4 Optional flatMap Versus map 156
6.5 Mapping Optionals 160
7. File I/O. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 165
7.1 Process Files 166
7.2 Retrieving Files as a Stream 169
7.3 Walking the Filesystem 170
7.4 Searching the Filesystem 172
vi | Table of Contents
8. The java.time Package. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 175
8.1 Using the Basic Date-Time Classes 176
8.2 Creating Dates and Times from Existing Instances 180
8.3 Adjusters and Queries 185
8.4 Convert from java.util.Date to java.time.LocalDate 190
8.5 Parsing and Formatting 194
8.6 Finding Time Zones with Unusual Offsets 197
8.7 Finding Region Names from Offsets 200
8.8 Time Between Events 202
9. Parallelism and Concurrency. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 205
9.1 Converting from Sequential to Parallel Streams 206
9.2 When Parallel Helps 209
9.3 Changing the Pool Size 215
9.4 The Future Interface 217
9.5 Completing a CompletableFuture 220
9.6 Coordinating CompletableFutures, Part 1 225
9.7 Coordinating CompletableFutures, Part 2 231
10. Java 9 Additions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 239
10.1 Modules in Jigsaw 240
10.2 Private Methods in Interfaces 245
10.3 Creating Immutable Collections 247
10.4 Stream: ofNullable, iterate, takeWhile, and dropWhile 252
10.5 Downstream Collectors: filtering and flatMapping 255
10.6 Optional: stream, or, ifPresentOrElse 259
10.7 Date Ranges 262
A. Generics and Java 8. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 267
Index. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 287
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