Java Idioms for becoming a more powerful developer

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Java Idioms
Jeanne Boyarsky

Wednesday June 21, 2023

KCDC

speakerdeck.com/boyarsky

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About Me
• Java Champion

• Author

• Developer at NYC
bank for 21+
years

• FIRST Robotics
Mentor
2

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Pause for a Commercial
3
Java certs: 8/11/17

Book giveaway at end!

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Disclaimer
• A bit of the material is from my
books.

• Some of the material in this
presentation may appear in
our upcoming certification
books.
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Introductions
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Agenda
• Strings and Text Blocks

• Regular Expressions

• Collections & Streams

• File I/O + Other Useful APIs
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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.
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Idiom
• Recurring construct

• Has meaning

• Common approach
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Design Patterns
• Typically higher level

• May be language agnostic
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Anti-Pattern
• Common “solution”

• Negative effects
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Example #1 - What is it?
11
Design Pattern

(Singleton)

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Idiom

(Pre-Java 8)

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13
Anti-pattern

* catches “Exception”

* ignores exception

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Agenda



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Is there a match?
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IntelliJ warning!

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Is there a match?

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Only whitespace
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Even Better
19
Java 11
Java 11

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String Concatentation
20
Best choice
changes over time

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Equal?
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Case Insensitive Equal
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Case Insensitive Compare
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Creating Csv
24
Better to use
Commons
CSV Library

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Multiples
25
Java 11

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Formatting
• %s - string

• %d - int

• %f - float/double (minimum width/precision)

• %n - new line

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Formatting
Java 15

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Text Blocks
28
Java 15

(adds line breaks)

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Text Blocks
29
incidental

whitespace
essential

whitespace
no trailing

new line
quote not

escaped

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Other “new” APIs
API Introduced
stripLeading()

stripTrailing()

lines()
11
indent(number) 12
transform(function) 12
stripIndent()

translateEscapes()
15
indexOf(ch, beginIndex, endIndex)

indexOf(str, beginIndex, endIndex)
21
splitWithDelimiters(regex, limit) 21

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Review - What best API?
• Check if String empty?

• Duplicate String?

• Merge Strings?

• Compare case sensitive
strings?

• Compare non-case sensitive
strings?
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Lab
32
Do NOT use streams or lambdas

in this lab

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Lab & Break
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https://github.com/boyarsky/
2023-kcdc-java-idioms

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Agenda



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Lab Review
• Any questions?

• How did you solve Tic Tac Toe?
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Remove all Numbers
36
Note replaceAll
What are two ways to remove
blank spaces too?

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Remove leading pattern
37
Three changes:

replaceFirst()

^

+

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Remove trailing pattern
38
Watch escaping

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Remove middle
39
Off by one error?

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Ugly regex
40

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Better regex
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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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Brainstorm
43
How many ways can we match

one or more using at most

2 x characters?

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Splitting on a Regex
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Contains only digits
45

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Contains any digits
46
More to regex

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Case Insensitive
47

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Case Insensitive
48

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Multi Line Replace
49
(?m)

Also $1
a

b

c

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Dot All
50
(?s)

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Pattern Idiom
51

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Pattern Replace
52

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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?
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Lab & Break
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Agenda



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Lab Review
• Any questions?

• Did you like replaceAll() or
Pattern better?

• What was hardest?
56

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Create a Set
57
Java 9

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Create a List
58
Java 9

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Mutable List
59
Java 9

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Mutable Copy
60

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Immutable Copy
61
Java 10

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Synchronized View
62

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Unmodifiable View
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Create a Map
64

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Create a Map
65
Java 9

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Sorting
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Sorting
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Removing from a List
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Element in List
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Replacing
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Venn Diagram?
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Defaulting
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Add to map if not present
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Other Useful Map Methods
• containsKey(), containsValue()

• entrySet()

• keySet(), values()

• remove(key)

• remove(key, value)

• replace(key, value)

• replace(key, oldValue, newValue)
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Printing
75

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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
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Find max
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Join a String
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Get First Elements
79
Java 9
and 16

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Get element
80
Java 9

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Strings
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Useful Terminal Operations
• count()

• collect() - more on this next module

• allMatch(), anyMatch(), noneMatch()

• findFirst(), findAny()

• min()/max()

• forEach()

• toArray, toList()
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Useful Intermediate Operations
• filter()

• map()

• distinct()

• limit(), skip()

• sorted()

• peek()
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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?
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Infinite: Generating
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Infinite: Iterative
86
Java 9

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FlatMap
87

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Creating Map
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Creating Map With Conflict
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Grouping By Key
90

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Partitioning By Key
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Grouping By Key
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Reduce
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Review
• Sources

• generate()

• iterate()

• Intermediate

• flatMap()

• Terminal

• reduce()

• Collectors

• toMap()

• groupingBy()

• partitioningBy()
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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?
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Lab & Break
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Agenda



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Lab Review
• How did you feel about longer
streams?

• Did you see how different
methods are useful for
different problems?
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@jeanneboyarsky
Records
99
Java 16
Ran out of room
on the screen

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@jeanneboyarsky
Records
100
Automatically get

* final record

* private final instance
variables

* public accessors

* constructor taking both
fields

* equals

* hashCode

Can @Override any
methods (ex: backward
compatibility for getters)

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Creating a Path
101

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Absolute Path
102

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Separators
103
Windows:

\\ and ;
Mac/Linux:

/ and :

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Read File into String
104
Java 11

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Read File into List
105

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Read File with Stream
106

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Write File from String
107
Java 11

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Write File from List
108

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Append To File
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Walk Tree
110

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Convert to unchecked
111
Or
unchecked
wrapper

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Delete File
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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?
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Math
114

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Math
115

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Random
116

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Random
117

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Random
118

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Random
119

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LocalDate
120

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LocalDate
121

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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?
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Win a book
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Lab & Break
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Java Idioms for becoming a more powerful developer

Java Idioms for becoming a more powerful developer

Jeanne Boyarsky

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