Introduction

• What I want to accomplish: I want to move toAmazon Corretto 15 so I can use the new features in my work projects. These features feel long awaited; So much so,Kotlin andLombok continue to gain popularity.
• How: I plan to convert an existing Java project from amazon‑corretto‑11 to amazon‑corretto‑15,and add code to the project which will leverage the new features just to see how our infrastructure handles them.
• Caveats: This particular service is dockerized. So we would also need to update our docker image to use Java 15. I plan to run the project outside of docker just usingmvn from a local shell.

Conversion process

Change the Maven compiler plugin version.

In the build section of thepom.xml file:

<build><plugins>            . . .<plugin><artifactId>maven-compiler-plugin</artifactId><version>3.8.1</version><configuration><release>15</release><compilerArgs><arg>--enable-preview</arg></compilerArgs></configuration></plugin>            . . .<plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-surefire-plugin</artifactId><configuration><forkCount>0</forkCount><argLine>--enable-preview</argLine></configuration></plugin>            . . .<plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-failsafe-plugin</artifactId><configuration><argLine>--enable-preview</argLine></configuration></plugin></plugins><build>

I neededforkCount in thesurefire plugin configuration because the parent pom declares something higher than0,SUREFIRE-1528.

This is a great reminder that some of the features in 15 are technically experimental still and require preview.
While I would be hesitant to use preview features in a production system, Amazon hasfaithfully iterated on corretto-11 through patches. Thus, as issues arise, there is iteration to fix those problems, and I believe that would also extend to preview features.
And I think it's safe to assume thatcorretto-15 will also have patches issued.

Installing Amazon Corretto 15

Downloadamazon-corretto-15

Or for the Linux users, you couldn't ask for a sweeter time:Linux package managed installation instructions

Updating my IDE

IntelliJ

Download the latest IntelliJ and you will have been all set to useJava 15 since version 2020.2!

Eclipse

Download the latest Eclipse

Using the JDK

Just make sure when you're setting up your IDE, that you point to the correctto JDK installation!

Let's try out these Java 15 features

No more need for lombok here | Records

Here is a simple class in the existing project. Users in this domain are given a "baby step" between0 and7.

With Lombok:

@lombok.DatapublicclassUserBabyStep{publicstaticfinalUserBabyStepNO_BABY_STEP=newUserBabyStep();publicstaticfinalintDEFAULT_BABY_STEP=0;publicstaticfinalintMAX_BABY_STEP=7;privatefinalintvalue;publicUserBabyStep(){this.value=DEFAULT_BABY_STEP;}publicUserBabyStep(finalintvalue){if(value<0||value>MAX_BABY_STEP)thrownewIllegalArgumentException("The Baby Step of a user must be between 0 and 7 inclusively.");this.value=value;}}

Hellorecords!

publicrecordUserBabyStep(intvalue){publicstaticfinalUserBabyStepNO_BABY_STEP=newUserBabyStep();publicstaticfinalintDEFAULT_BABY_STEP=0;publicstaticfinalintMAX_BABY_STEP=7;publicUserBabyStep(){this(DEFAULT_BABY_STEP);}publicUserBabyStep(finalintvalue){if(value<0||value>MAX_BABY_STEP)thrownewIllegalArgumentException("The Baby Step of a user must be between 0 and 7 inclusively.");this.value=value;}}

Notes forrecord

Lombok will generate a more Java‑canonical getter method for fields:getValue(). The getter method produced by therecord feature is:value().
This is more similar to how theImmutables library operates, andis a fancy way to get around when you may, or may not wantisFlag forboolean getters. Especially if you are like me, and prefer leveraging the type system for wrapping primitives in a more domain‑driven class.

Another note is thatrecord‑declared classescannot extend another class! Only implement interfaces.

Necessary usage of the canonical constructor

Finally, when using records, all constructorsmust call the canonical constructor. That is, the constructor with the same types, order, and number of arguments that are declared on the record itself.

Who's up for Checkers?

Instead of just looking for more things to change around in this existing project, I'm going to add irrelevant code simply for the sake of flexing the new features. And then, I want to see how it compiles and how the project plugins handle it.

Also, I isolated thecheckers code if you'd like to take a closer look.

Sealed Interfaces

I'm going to mess around with this here, however, see the note at the end of the article concerning sealed interfaces.

A checker board tends to have two alternating colors tiling a 8 x 8 board.

Eachspace/tile can havecontents; a red or black token.

To demonstrate the difference between individual tiles, there is a sealed interface calledSpace whichpermits aBlackSpace and aRedSpace. Each subclass then also implements thewither method that allows a space to take new contents.

publicenumContents{EMPTY,BLACK,RED;}publicstaticsealedinterfaceSpacepermitsBlackSpace,RedSpace{publicContentscontents();publicintx();publicinty();publicSpacewithContents(finalContentsstate);publicdefaultbooleanisEmpty(){returncontents()==Contents.EMPTY;}publicdefaultbooleancontains(finalContentsstate){returncontents()==state;}publicrecordBlackSpace(Contentscontents,intx,inty)implementsSpace{publicBlackSpace(finalintx,finalinty){this(Contents.EMPTY,x,y);}@OverridepublicSpacewithContents(finalContentscontents){returnnewBlackSpace(contents,x,y);}}publicrecordRedSpace(Contentscontents,intx,inty)implementsSpace{publicRedSpace(finalintx,finalinty){this(Contents.EMPTY,x,y);}@OverridepublicSpacewithContents(finalContentscontents){returnnewRedSpace(contents,x,y);}}}

Now ourCheckerBoard can look a little something like this:

@SuppressWarnings("preview")publicclassCheckerBoard{privatestaticintMAX=8;privatefinalSpace[][]spaces;privateCheckerBoard(){spaces=newSpace[MAX][MAX];forEachSpace((i,j)->spaces[i][j]=((i+j)%2==0)?newBlackSpace(i,j):newRedSpace(i,j));}...}

Note: that, if you are anything like me, you aren't a fan of warnings. So here's a way tosuppress them for the preview features we'll be using.

Multi-line Strings

Java eliminates all leading whitespace between newlines!
Luckily, I already had a scenario where I would not need leading spaces in my string anyways:

classCheckerBoardTest{@TestvoidshouldPrintBoardAsExpected(){finalCheckerBoardsubject=CheckerBoard.freshBoardWithTokens();assertThat(subject.toString()).isEqualTo("""            Ω · Ω · Ω · Ω ·            · Ω · Ω · Ω · Ω            Ω · Ω · Ω · Ω ·            · • · • · • · •            • · • · • · • ·            · ☺ · ☺ · ☺ · ☺            ☺ · ☺ · ☺ · ☺ ·            · ☺ · ☺ · ☺ · ☺            """);}}

The google format spec basically has no idea what to do with this…

Pattern Matching ininstanceof (instanceof casting)

This is a really handy trick that I wish was introduced much earlier.

It is also reminiscent ofa feature of the AssertJ testing library.

The key use of this feature is to prevent a manual class cast of a variable after you areonly in a block of code based on the type of a variable.

So instead of:

publicvoidmethod(finalAnimalanimal){if(animalinstanceofCat){((Cat)animal).meow();}}

We can do:

publicvoidmethod(finalAnimalanimal){if(animalinstanceofCatcat){cat.meow();}}

This method will set up a new checkboard and place the players' tokens in their starting positions. Since pieces should only be allowed to be played to the black spaces on the board, I can place pieces using the awither to keep eachspace instance of my board immutable.

publicstaticCheckerBoardfreshBoardWithTokens(){finalCheckerBoardboard=newCheckerBoard();board.forTopThreeRowsOfSpaces(space->{if(spaceinstanceofBlackSpaces){board.spaces[s.x()][s.y()]=s.withContents(BLACK);}});board.forBottomThreeRowsOfSpaces(space->{if(spaceinstanceofBlackSpaces){board.spaces[s.x()][s.y()]=s.withContents(RED);}});returnboard;}

To be fair, the cast here is not necessary. So if you can come up with a better use case, I'd be happy to hear about it in the comments!

Switch Expression

OurCheckerBoard class has a convenienttoString method for a user friendly visual:

@OverridepublicStringtoString(){returnstreamSpaces().map(space->{finalStringstrSpace=(switch(space.contents()){caseEMPTY:yieldspaceinstanceofRedSpace?"·":"•";caseBLACK:yield"Ω";caseRED:yield"☺";});returnString.format("%s%s",strSpace,space.isRightEdge()?"\n":" ");}).reduce(newStringBuilder(),StringBuilder::append,(l,r)->l).toString();}

That newyield keyword at work! I can essentially iterate over eachspace to yield a character.

More examples can be found here at thisBaeldung article.

Issues

• google code formatter breaks. It looks like it breaks on records, multi-line strings, and theyield keyword that occurs in the switch expressions
  • To solve this, I think some motivated person could just start collaborating on Google GitHub repos for this.The spec repoThe configuration repo
• the maven compiler (actually, the JVM) requires the--enable-preview flag to unlock the features. This is an obvious red flag for usage in production code. It is hard to assess the risk of using these features as well. In the past, many features of the JDK that shipped as previews in earlier versions of Java have actually functioned perfectly. Will that continue to be the case?

Wrap-up

One cannot simply assume thatpreview Java feature will become integrated into the JDK long‑term.
TheJavaDoc for theRecord class even contains a disclaimer:

This class is associated withrecords, a preview feature of the Java language. Programs can only use this class when preview features are enabled. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.

In the case ofrecords, however, you can breathe easy, as it isofficially integrated into Java 16.

As for the other features described in this article:

Sealed interfaces are still not officially being integrated. Even if they stick around, their syntax is subject to change. So that isn't a feature we were able to use here yet.

The other features that I listed as being integrated for version 16, have not changed syntactically since 15, (as far as I could tell). So with those, you're in the clear

Verdict

If you don't care about using the Google code formatter plugin for a while, and don't care about using sealed interfaces yet, you and your team can make the upgrade!

If for some reason you are still tempted to use the sealed interfaces anyways, I would strongly suggest not using them! It is not an officially integrated feature and could change or even go away.
A good example of this was the "Switch Expressions" feature. It was introduced in version 12 and overloaded thebreak keyword. This was changed toyield in version 13 to make more clear the intended behavior. Since it changed, it naturally needed to stay in preview in version 13, then finally was accepted in version 14. There's no telling what kind of iteration the sealed interfaces could still undergo.

Complete side-note | Speaking of features coming and going or staying

Sometimes, it is nice to declare aFunction in a Java Lambda, but you plan to return a specific object regardless of the input. In the past, I have used an underscore_ to define the variable of non-interest.Java 9 had discontinued this from being allowed.
Which I found interesting, considering that the introduction of_ as a variable name, had the apparent intention of being used inlambdas for unused arguments.

While in our code bases, we have now switched to using double underscores__ for this, we also use Vavr. So a nice alternative might be to useFunction1.constant.