Java Idioms - Speaker Deck

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

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

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

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@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

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@jeanneboyarsky Introductions 5

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

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@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

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

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

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

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

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

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

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@jeanneboyarsky Example #4 - What is it? 14

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 15

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@jeanneboyarsky Is there a match? 16 IntelliJ warning!

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@jeanneboyarsky 17 Is there a match?

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@jeanneboyarsky Only whitespace 18

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@jeanneboyarsky Even Better 19 Java 11 Java 11

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@jeanneboyarsky String Concatentation 20 Best choice changes over time

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@jeanneboyarsky Equal? 21

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@jeanneboyarsky Case Insensitive Equal 22

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@jeanneboyarsky Case Insensitive Compare 23

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@jeanneboyarsky Creating Csv 24 Better to use Commons CSV Library

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@jeanneboyarsky Multiples 25

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

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@jeanneboyarsky Pass Mock object 27

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@jeanneboyarsky And Test 28

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@jeanneboyarsky If Cannot Change 29

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

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

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

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

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 34

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

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

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

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@jeanneboyarsky Remove trailing pattern 38 Watch escaping

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@jeanneboyarsky Remove middle 39 Off by one error?

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@jeanneboyarsky Ugly regex 40

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@jeanneboyarsky Better regex 41

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@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

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@jeanneboyarsky Splitting on a Regex 43

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@jeanneboyarsky Contains only digits 44

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@jeanneboyarsky Contains any digits 45 More to regex

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@jeanneboyarsky Case Insensitive 46

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@jeanneboyarsky Case Insensitive 47

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

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@jeanneboyarsky Dot All 49 (?s)

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@jeanneboyarsky Pattern Idiom 50

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@jeanneboyarsky Pattern Replace 51

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@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

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@jeanneboyarsky Lab & Break 53 https://github.com/boyarsky/2020- devnexus-java-idioms

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 54

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

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@jeanneboyarsky Create a Set 56 Java 9

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@jeanneboyarsky Create a List 57 Java 9

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@jeanneboyarsky Mutable List 58 Java 9

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@jeanneboyarsky Mutable Copy 59

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@jeanneboyarsky Immutable Copy 60 Java 10

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@jeanneboyarsky Synchronized View 61

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@jeanneboyarsky Unmodifiable View 62

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@jeanneboyarsky Create a Map 63

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@jeanneboyarsky Create a Map 64 Java 9

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@jeanneboyarsky Sorting 65

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@jeanneboyarsky Sorting 66

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@jeanneboyarsky Removing from a List 67

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@jeanneboyarsky Element in List 68

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@jeanneboyarsky Replacing 69

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@jeanneboyarsky Venn Diagram? 70

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@jeanneboyarsky Defaulting 71

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@jeanneboyarsky Add to map if not present 72

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

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@jeanneboyarsky Printing 74

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@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

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@jeanneboyarsky Lab & Break 76 https://github.com/boyarsky/2020- devnexus-java-idioms

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 77

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

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

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@jeanneboyarsky Stream Flow 80 Intermediate Operations Source Terminal Operation

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

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

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

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@jeanneboyarsky Basic Stream 84

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@jeanneboyarsky Find max 85

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@jeanneboyarsky Join a String 86

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@jeanneboyarsky Get First Elements 87 Java 9

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@jeanneboyarsky Get element 88 Java 9

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@jeanneboyarsky Strings 89

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

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

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@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

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@jeanneboyarsky Lab & Break 93 https://github.com/boyarsky/2020- devnexus-java-idioms

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 94

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@jeanneboyarsky Lab Review • Did you get them all? • Which was your longest solution? • What did you come up with for takeWhile() or dropWhile()? 95

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@jeanneboyarsky Infinite: Generating 96

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@jeanneboyarsky Infinite: Iterative 97 Java 9

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@jeanneboyarsky FlatMap 98

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@jeanneboyarsky Creating Map 99

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@jeanneboyarsky Creating Map With Conflict 100

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@jeanneboyarsky Grouping By Key 101

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@jeanneboyarsky Partitioning By Key 102

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@jeanneboyarsky Grouping By Key 103

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@jeanneboyarsky Reduce 104

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

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@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

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@jeanneboyarsky Lab & Break 107 https://github.com/boyarsky/2020- devnexus-java-idioms

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 108

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@jeanneboyarsky Lab Review • Did you get them all? • How did you solve the challenge problem? • Did you see how different methods are useful for different problems? 109

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@jeanneboyarsky Creating a Path 110

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@jeanneboyarsky Absolute Path 111

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

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@jeanneboyarsky Read File into String 113 Java 11

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@jeanneboyarsky Read File into List 114

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@jeanneboyarsky Read File with Stream 115

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@jeanneboyarsky Write File from String 116 Java 11

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@jeanneboyarsky Write File from List 117

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@jeanneboyarsky Append To File 118

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@jeanneboyarsky Walk Tree 119

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@jeanneboyarsky Convert to unchecked 120 Or unchecked wrapper

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@jeanneboyarsky Delete File 121

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@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? 122

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@jeanneboyarsky Lab & Break 123 https://github.com/boyarsky/2020- devnexus-java-idioms

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@jeanneboyarsky Agenda • Strings • Regular Expressions • Collections • Streams • Advanced Streams • File I/O • Other Useful APIs 124

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@jeanneboyarsky Lab Review • Did you get them all? • How did you solve the challenge problem? • Which seemed easier - reading all lines or lines() for the odd/ even problem? 125

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@jeanneboyarsky Math 126

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@jeanneboyarsky Math 127

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@jeanneboyarsky Random 128

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@jeanneboyarsky Random 129

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@jeanneboyarsky Random 130

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@jeanneboyarsky Random 131

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@jeanneboyarsky LocalDate 132

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@jeanneboyarsky LocalDate 133

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@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

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

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@jeanneboyarsky Lab & Break 136 https://github.com/boyarsky/2020- devnexus-java-idioms