Java Idioms

@jeanneboyarsky 1 Java Idioms Jeanne Boyarsky Wednesday February 19, 2020
DevNexus speakerdeck.com/boyarsky

@jeanneboyarsky About Me • Java Champion • Author • Developer
at NYC bank for 17+ years • FIRST Robotics Mentor 2

@jeanneboyarsky Pause for a Commercial 3 Java 11 certs •1Z0-815
- Out now •1Z0-816 - April ETA

@jeanneboyarsky Disclaimer • A bit of the material is from
my books. • Some of the material in this presentation may appear in our upcoming certification books. 4

@jeanneboyarsky Introductions 5

@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections •
Streams • Advanced Streams • File I/O • Other Useful APIs 6

@jeanneboyarsky Module Flow •Review lab from previous module •Lecture/review •Hands
on exercises •10 minute break This means if a colleague needs to call you, the last 15-20 minutes of each hour is best. 7

@jeanneboyarsky Idiom • Recurring construct • Has meaning • Common
approach 8

@jeanneboyarsky Design Patterns • Typically higher level • May be
language agnostic 9

@jeanneboyarsky Anti-Pattern • Common “solution” • Negative effects 10

@jeanneboyarsky Example #1 - What is it? 11 Design Pattern
(Singleton)

@jeanneboyarsky Example #2 - What is it? 12 Idiom (Pre-Java
8)

@jeanneboyarsky Example #3 - What is it? 13 Anti-pattern *
catches “Exception” * ignores exception

@jeanneboyarsky Example #4 - What is it? 14

@jeanneboyarsky Is there a match? 16 IntelliJ warning!

@jeanneboyarsky 17 Is there a match?

@jeanneboyarsky Only whitespace 18

@jeanneboyarsky Even Better 19 Java 11 Java 11

@jeanneboyarsky String Concatentation 20 Best choice changes over time

@jeanneboyarsky Equal? 21

@jeanneboyarsky Case Insensitive Equal 22

@jeanneboyarsky Case Insensitive Compare 23

@jeanneboyarsky Creating Csv 24 Better to use Commons CSV Library

@jeanneboyarsky Multiples 25

@jeanneboyarsky How do I unit test this? 26 can edit?
pass in a mock stub out real System.out Yes No

@jeanneboyarsky Pass Mock object 27

@jeanneboyarsky And Test 28

@jeanneboyarsky If Cannot Change 29

@jeanneboyarsky Formatting • %s - string • %d - int
• %f - float/double (minimum width/precision) • %n - new line

@jeanneboyarsky Review - What best API? • Check if String
empty? • Duplicate String? • Merge Strings? • Compare case sensitive strings? • Compare non-case sensitive strings? 31

@jeanneboyarsky Lab 32 Do NOT use streams or lambdas in
this lab

@jeanneboyarsky Lab & Break 33 https://github.com/boyarsky/2020- devnexus-java-idioms

@jeanneboyarsky Lab Review • Any questions? • How did you
solve Tic Tac Toe? 35

@jeanneboyarsky Remove all Numbers 36 Note replaceAll What are two
ways to remove blanks spaces too?

@jeanneboyarsky Remove leading pattern 37 Three changes: replaceFirst() ^ +

@jeanneboyarsky Remove trailing pattern 38 Watch escaping

@jeanneboyarsky Remove middle 39 Off by one error?

@jeanneboyarsky Ugly regex 40

@jeanneboyarsky Better regex 41

@jeanneboyarsky Regex quick reference 42 0 or more * 1
or more + 0 or 1 ? any . three x’s x{3} range [0-9] Not in range [^0-9] Digit \d White space \s Word \w

@jeanneboyarsky Splitting on a Regex 43

@jeanneboyarsky Contains only digits 44

@jeanneboyarsky Contains any digits 45 More to regex

@jeanneboyarsky Case Insensitive 46

@jeanneboyarsky Case Insensitive 47

@jeanneboyarsky Multi Line Replace 48 (?m) Also $1 a b
c

@jeanneboyarsky Dot All 49 (?s) <form> <input /> <textarea />
</form>

@jeanneboyarsky Pattern Idiom 50

@jeanneboyarsky Pattern Replace 51

@jeanneboyarsky Review - How do I? • Match digit? •
Remove a single match? • Treat dot as any character? • Match a character 100 times? • Loop through matches? • Match a period? 52

@jeanneboyarsky Lab Review • Any questions? • Did you like
replaceAll() or Pattern better? • What was hardest? 55

@jeanneboyarsky Create a Set 56 Java 9

@jeanneboyarsky Create a List 57 Java 9

@jeanneboyarsky Mutable List 58 Java 9

@jeanneboyarsky Mutable Copy 59

@jeanneboyarsky Immutable Copy 60 Java 10

@jeanneboyarsky Synchronized View 61

@jeanneboyarsky Unmodifiable View 62

@jeanneboyarsky Create a Map 63

@jeanneboyarsky Create a Map 64 Java 9

@jeanneboyarsky Sorting 65

@jeanneboyarsky Sorting 66

@jeanneboyarsky Removing from a List 67

@jeanneboyarsky Element in List 68

@jeanneboyarsky Replacing 69

@jeanneboyarsky Venn Diagram? 70

@jeanneboyarsky Defaulting 71

@jeanneboyarsky Add to map if not present 72

@jeanneboyarsky Other Useful Map Methods • containsKey(), containsValue() • entrySet()
• keySet(), values() • remove(key) • remove(key, value) • replace(key, value) • replace(key, oldValue, newValue) 73

@jeanneboyarsky Printing 74

@jeanneboyarsky Review - How do I? • Create an immutable
copy • Remove all values less than 5 • Update the value in a map if the current value is 10 • Return 0 if the value isn’t found • Find the intersection of two collections 75

@jeanneboyarsky Lab Review • Did you get them all? •
Which was your longest solution? • How many ways did you get the challenge question? 78

@jeanneboyarsky Optional 79 Optional.empty() Optional.of(95) 95

@jeanneboyarsky Stream Flow 80 Intermediate Operations Source Terminal Operation

@jeanneboyarsky Painting Example 81 1 2 3 4 5 6
Take sign out of box Put sign in pile Intermediate Operations Paint sign

@jeanneboyarsky Painting Example 82 Take sign out of box Put
sign in pile Intermediate Operations Only do 2 signs Paint sign

@jeanneboyarsky Painting Example 83 stream() forEach() Intermediate Operations filter() limit()
sorted()

@jeanneboyarsky Basic Stream 84

@jeanneboyarsky Find max 85

@jeanneboyarsky Join a String 86

@jeanneboyarsky Get First Elements 87 Java 9

@jeanneboyarsky Get element 88 Java 9

@jeanneboyarsky Strings 89

@jeanneboyarsky Useful Terminal Operations • count() • collect() - more
on this next module • allMatch(), anyMatch(), noneMatch() • findFirst(), findAny() • min()/max() • forEach() 90

@jeanneboyarsky Useful Intermediate Operations • filter() • map() • distinct()
• limit(), skip() • sorted() • peek() 91

@jeanneboyarsky Review - What method can… • Return whether 5/5
values == 7? • Return whether >=1 values == 7? • Make a stream smaller? • Change the order of stream elements? • Loop through stream elements? • Ignore the first 2 elements? • Ignore any elements are the first 2? 92

Which was your longest solution? • What did you come up with for takeWhile() or dropWhile()? 95

@jeanneboyarsky Infinite: Generating 96

@jeanneboyarsky Infinite: Iterative 97 Java 9

@jeanneboyarsky FlatMap 98

@jeanneboyarsky Creating Map 99

@jeanneboyarsky Creating Map With Conflict 100

@jeanneboyarsky Grouping By Key 101

@jeanneboyarsky Partitioning By Key 102

@jeanneboyarsky Grouping By Key 103

@jeanneboyarsky Reduce 104

@jeanneboyarsky Review • Sources • generate() • iterate() • Intermediate
• flatMap() • Terminal • reduce() • Collectors • toMap() • groupingBy() • partitioningBy() 105

@jeanneboyarsky What method for? • Creating an infinite stream of
a times table? • Creating a Map that always has two keys? • Creating a Map with a custom key/ value? • Returning an Optional representing the stream? 106

How did you solve the challenge problem? • Did you see how different methods are useful for different problems? 109

@jeanneboyarsky Creating a Path 110

@jeanneboyarsky Absolute Path 111

@jeanneboyarsky Separators 112 Windows: \\ and ; Mac/Linux: / and
:

@jeanneboyarsky Read File into String 113 Java 11

@jeanneboyarsky Read File into List 114

@jeanneboyarsky Read File with Stream 115

@jeanneboyarsky Write File from String 116 Java 11

@jeanneboyarsky Write File from List 117

@jeanneboyarsky Append To File 118

@jeanneboyarsky Walk Tree 119

@jeanneboyarsky Convert to unchecked 120 Or unchecked wrapper

@jeanneboyarsky Delete File 121

@jeanneboyarsky What API to? • Read file into a single
string? • Write a List to a file? • Get rid of a file? • List all files in directory? • Add to a file? • Process file as a Stream<String>? 122

How did you solve the challenge problem? • Which seemed easier - reading all lines or lines() for the odd/ even problem? 125

@jeanneboyarsky Math 126

@jeanneboyarsky Math 127

@jeanneboyarsky Random 128

@jeanneboyarsky LocalDate 132

@jeanneboyarsky LocalDate 133

@jeanneboyarsky What API to? • Get today? • Get July
4th of this year? • Create a random number between 2 and 10? • Get the largest value of two? • Get a unique id? 134

@jeanneboyarsky Before the last lab: Tomorrow 10:20am Java: Did you
know that? + Win a book 135

Java Idioms

Java Idioms

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