Refactoring to Java 17 and Beyond

@jeanneboyarsky mastodon.social/@jeanneboyarsky 1
Refactoring to Java 21 and beyond
Jeanne Boyarsky

August 23, 2023

Philly JUG

speakerdeck.com/boyarsky

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@jeanneboyarsky mastodon.social/@jeanneboyarsky
Commercial
2
Java certs: 8/11/17

Book giveaway at end!

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At end of session
https://speakerdeck.com/boyarsky
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Version of Java?
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Version of Java?
5
Version Plan
7 Upgrade ASAP. Even
extended support is over.
8 or 11 Align code to future. “older
Java comments”
9-10, 12-16, 18-19 Upgrade; not on latest LTS
17 Lots of refactoring
20-21 Even more refactoring

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For each Topic
• Example

• About the feature

• Opportunities

• IDE Support

• What to do if on older Java
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Refactoring
• We are writing legacy code now!

• Refactor for future compatibility
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Text blocks and Strings

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Example: REST API Params
public String getJson(String search) {
String json = "{" +
" \"query\": \"%s\"" +
" \"start\": \"1\"," +
" \"end\": \"10\"" +
"}";
return String.format(json, search);
}
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This is hard to read

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Take Two
Path path = Path.of(
“src/main/resources/query.json");
String json = null;
try {
json = Files.readString(path);
} catch (IOException e) {
throw new UncheckedIOException(e);
}
}
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Now the String is far away

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Text Block
String json = """
{
"query": "%s"
"start": "1"
"end": "10"
}""";
}
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It’s a string literal!
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Adds line breaks, but still works

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Text Block Syntax
String textBlock = """
kcdc,Kansas City,"session,workshop"
meetup,Various,lecture
""";
incidental
whitespace
start block
end block
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12

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Essential Whitespace

Jeanne Boyarsky

""";
incidental
whitespace
essential whitespace
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Ending lines

Jeanne Boyarsky \s

Becoming one of the first Java 17 \
certified programmers \
(and learning new features)

""";
continue on next line

without a line break
new escape character

keeps trailing whitespace
tab
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14

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New lines
\n

Jeanne\nBoyarsky

""";
no line break at end
Two new lines

(explicit and implicit)
One new line (explicit)
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15

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Escaping Three Quotes
better \"""
but can do \"\"\"
""";
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Opportunities
•Externalized data

•Expected values in JUnit

•Formats - CSV, GraphQL, JSON,
SQL, Text, XML, YAML, etc

•Others?
15
17

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IDE Support
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String json = """
{ "query": "%s" "start": "1", "end": "10"}""";
Literal refactoring - no \n

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IDE Support
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String json = """

{\

"query": "%s"\

"start": "1",\

"end": "10"\

}"""; Preserve lines but still no \n

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On older Java?
//TODO convert to text block when on Java 17
String json = "{" +
" \"query\": \"%s\"" +
" \"start\": \"1\"," +
" \"end\": \"10\"" +
"}";
}
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Hard to read but positions for future

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JavaDoc

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Java 5+ Options
/**
*
* List<String> getNames() {
*
* }
*
*
* List<String> getNames() { }

*
* @code List getNames {}}
*/
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Combined
/**
* @code
* List getNames() {
*
* }
* }
*/
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No HTML

IDE limitations: recognize, syntax highlighting, etc

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Inline Snippet
/**

* {@snippet :

* List getNames() {

*

* }

* }

*/

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18
Limitations:

No /* */ comments

Must have balanced pairs of {}

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Extended Snippet
/**

* {@snippet file=“JavaClass.java" region="section"}

*/

// @start region=“section"
/* many lines */
// @end
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Real files editable in your IDE

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Opportunities
•More/better code examples

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26
•Others?

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On older Java?
//TODO switch to snippet on Java 21
/**
* @code
* List getNames() {
*
* }
* }
*/
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Positions for future

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On older Java?
//TODO use external snippet on Java 21
using ThisClass.java
/**
* @code
* List getNames() {
*
* }
* }
*/
// @start region=“section"
// @end
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Records

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Originally
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Ran out of room

on screen!

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Record 16
public record Book (String title, int numPages) {
}
New type Automatically get

* final record

* private final instance variables

* public accessors

* constructor taking both fields

* equals

* hashCode

* toString
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Using the Record 16
Book book = new Book("Breaking and entering", 289);
System.out.println(book.title());
System.out.println(book.toString());
No “get”
Outputs:

Breaking and entering

Book[title=Breaking and entering, numPages=289]
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Opportunities
•Immutable POJOs

•Don’t have to write equals/
hashCode

•Vs reflection - EqualsBuilder

•Make code coverage tool happy

•Others?
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IDE Support
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public record Book(String title, int numPages) {
}
Had to make instance variables final. Also didn’t
remove my equals() even though generated by IntelliJ

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On older Java?
//TODO convert to record when on Java 17
public final class Book {
private String title;
private int numPages;
public Book(String title, int numPages) {
this.title = title;
this.numPages = numPages;
}
public String title() {
return title;
}
public int numPages() {
return numPages;
}
// hash code, equals
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Be sure to use al
fields for equals/
hashCode

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Instanceof

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Casting
if (num instanceof Integer) {
Integer numAsInt = (Integer) num;
System.out.println(numAsInt);
}
if (num instanceof Double) {
Double numAsDouble = (Double) num;
System.out.println(numAsDouble.intValue());
}
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Casting 16
if (num instanceof Integer numAsInt) {
}
if (num instanceof Double numAsDouble) {
}
Pattern

variable
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Flow Scope 16
if (num instanceof Double d1
&& d1.intValue() % 2 == 0) {
System.out.println(d1.intValue());
}
if (num instanceof Double d2
|| d2.intValue() % 2 == 0) {
System.out.println(d2.intValue());
}
Does not

compile

because

d2 might
not be
double
Compiles
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Does this compile? 16
if (num instanceof Double n)
System.out.println(n.intValue());
if (num instanceof Integer n)
System.out.println(n);
Yes. Only in scope for if statement
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No. If statement is over
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if (!(num instanceof Double n)) {
return;
}
Yes. Returns early so rest is
like an else
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if (!(num instanceof Double n)) {
return;
}
No. n is still in scope
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Record Pattern 21
public static void titles(List books) {

for (var obj : books) {

if (obj instanceof Book(String title, int numPages)) {

System.out.println(title);

}

}

}

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Opportunities
•Library code

•Equals methods

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45
•Others?

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IDE Support
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if (num instanceof Integer numAsInt) {
}

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On older Java?
//TODO convert to pattern var when on Java 17
if (num instanceof Double) {
Double numAsDouble = (Double) num;
}
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Positions for future

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Switch expressions

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Originally
public String getLocation(String store) {
String result = "";
switch (store) {
case "Hallmark":
result = "KC";
break;
case "Crayola":
result = "PA";
break;
default:
result = "anywhere";
}
return result;
}
You remembered the breaks, right?
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Switch Expressions 14
return switch (store) {
case "Hallmark" -> "KC";
case "Crayola" -> "PA";
default -> "anywhere";
};
}
Arrow labels
No break keyword
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Missing value 14
enum Position { TOP, BOTTOM };
Position pos = Position.TOP;
int stmt = switch(pos) {
case TOP: yield 1;
};
int expr = switch(pos) {
case BOTTOM -> 0;
};
Does not compile
because assigning
value

(poly expression)
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Pattern matching for switch 21
public int toInt(Object obj) {
return switch (obj) {
case Integer i -> i;
case Double d -> d.intValue();
case String s -> Integer.parseInt(s);
default -> throw new
IllegalArgumentException("unknown type");
};
}
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But wait, there’s more 21
static void printOddOrEven(Object obj) {
switch (obj) {
case Integer i when i % 2 == 1 ->
System.out.println("odd");
case Integer i when i % 2 == 0 ->
System.out.println(“even");
default -> System.out.println("not an int");
};
}
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Opportunities
•Many if/else chains!

•Switch statements with many
breaks

•Sets the stage for advanced
matching

•Others?
17
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IDE Support
55
String result = switch (store) {
case "Hallmark" -> "KC";
case "Crayola" -> "PA";
default -> "anywhere";
};
return result;

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On older Java?
//TODO convert to switch expression on Java 17
String result = "";
switch (store) {
case "Hallmark":
result = "KC";
break;
case "Crayola":
result = "PA";
break;
default:
result = "anywhere";
}
return result;
}
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APIs

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Sequenced Collections
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21
• addFirst()

• addLast()

• getFirst()

• getLast()

• removeFirst()

• removeLast()

Set

• reversed()
Map

• reversed()

• sequencedKeySet()

• sequencedValues()

• sequencedEntrySet()

• putFirst(k, v)

• putLast(k, v)

from NavigableMap

• firstEntry()

• lastEntry()

• pollFirstEntry()

• pollLastEntry()

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toList()
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16
public List listLonger(
Stream stream) {
return stream.collect(Collectors.toList());
}
public List listShorter(
Stream stream) {
return stream.toList();
}

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Teeing Collector
60
12
record Separations(String spaceSeparated,
String commaSeparated) {}
var list = List.of("x", "y", "z");
Separations result = list.stream()
.collect(Collectors.teeing(
Collectors.joining(" "),
Collectors.joining(","),
(s, c) -> new Separations(s, c)));
System.out.println(result);

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Formatting a String
String firstName = "Jeanne";
String lastName = "Boyarsky";
String str = String.format(
"Hi %s %s!", firstName, lastName);
System.out.println(str);
System.out.println("Hi %s %s!".formatted(
firstName, lastName));
Outputs:

Hi Jeanne Boyarsky!

Hi Jeanne Boyarsky!
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Common Conversions
Conversion What it does
%s Formattable

as String
%d Decimal

integer

(no dot)
%c Char
%f Float

(decimal)
%n New line
Many more out of
scope. Examples:

• %e - scientific
notation

• %t - time

• %S - converts to all
uppercase
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Conversion Examples
Code Output
"%d%%".formatted(1.2) exception
"%d%%".formatted(1) 1%
"%s%%".formatted(1) 1%
"%s%%".formatted(1.2) 1.2%
“%f%%".formatted(1.2) 1.200000f
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Formatting a Number
Char What it does
- Left justified
+ Always

include

+/-
space Leading

space if

positive
Char What it does
0 Zero padded
, Group

numbers
( Negative # in

parens
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Flag Examples
Code Output
"%,d".formatted(1234) 1,234
"%+d".formatted(1234) 1234
“% d".formatted(1234) 1234
“%,(d”.formatted(-1234) (1,234)
“%,f”.formatted(
1.23456789)
1.234568
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Compact Number
NumberFormat defaultFormat =
NumberFormat.getCompactNumberInstance();
NumberFormat shortFormat = NumberFormat
.getCompactNumberInstance(
Locale.US, NumberFormat.Style.SHORT);
NumberFormat longFormat = NumberFormat
.getCompactNumberInstance(
Locale.US, NumberFormat.Style.LONG);
System.out.println(defaultFormat.format(1_000_000));
System.out.println(shortFormat.format(1_000_000));
System.out.println(longFormat.format(1_000_000));
1M

1M

1 million
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New Files.mismatch()
Path kcdc = Path.of("files/kcdc.txt");
Path kc = Path.of("files/kc.txt");
System.out.println(Files.mismatch(kcdc, kc));
System.out.println(Files.mismatch(kcdc, kcdc));
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11 (index of first character different)

-1 (same file contents regardless of whether exists)
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Virtual Threads
var ex = Executors.newThreadPerTaskExecutor()

vs

var ex = Executors.newVirtualThreadPerTaskExecutor()

ex.submit(runnOrCall)

// or managed

Thread.Builder b = Thread.ofPlatform().name("xxx");

vs

Thread.Builder b = Thread.ofVirtual().name("xxx");

b.start(runnable)
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This could be a whole presentation….
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Book Giveaway
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Refactoring to Java 17 and Beyond

Refactoring to Java 17 and Beyond

Jeanne Boyarsky

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