Java Next!

From Amber to Loom, from Panama to Valhalla

Developer Advocate

Java Team at Oracle

Accento 2023

  • Karlsruhe

  • October 24th, 25th

  • 50% discount: AccJUGCH23

I have two free tickets!

Lots to talk about!

Project Amber
Project Panama
Project Valhalla
Project Loom

Project Amber

Smaller, productivity-oriented Java language features



Some downsides of Java:

  • can be cumbersome

  • tends to require boilerplate

  • situational lack of expressiveness

Amber continuously improves that situation.


Pattern Matching

Amber’s main thrust is pattern matching:

  • improved switch

  • records

  • sealed types

  • pattern matching

Inside Java Newscast #29

inside java newscast 29

String composition

Composing strings in Java is cumbersome:

String property = "last_name";
String value = "Doe";

// concatenation
String query =
	"SELECT * FROM Person p WHERE p."
		+ property + " = '" + value + "'";
// formatting
String query =
	"SELECT * FROM Person p WHERE p.%s = '%s'"
		.formatted(property, value);

Comes with free SQL injection! 😳

String interpolation

Why not?

// (fictional syntax!)
String query =
	"SELECT * FROM Person p "
		+ "WHERE p.\{property} = '\{value}'";

Also comes with free SQL injection! 😳

String interpolation

SQL injections aren’t the only concern.

These also need validation and sanitization:


  • JSON

  • YAML

  • …​

All follow format-specific rules.

String templating

Enter String Templates (JEP 430):

String query = STR."""
	SELECT * FROM Person p
	WHERE p.\{property} = '\{value}'

Template expression ingredients:

  • template with embedded expressions
    ~> StringTemplate

  • template processor (e.g. STR):
    transforms StringTemplate into String*

Template procesor STR

String form = STR."""
	Desc     Unit   Qty   Amount
	\{desc} $\{price} \{qty} $\{price * qty}

	Subtotal  $\{price * qty}
	Tax       $\{price * qty * tax}
	Total     $\{price * qty * (1.0 + tax)}
Desc     Unit   Qty   Amount
hammer   $7.88  3     $23.64

Subtotal  $23.64
Tax       $3.546
Total     $27.186

Template processor FMT

String form = FMT."""
	Desc        Unit      Qty   Amount
	%-10s\{desc} $%5.2f\{price} %5d\{qty} $%5.2f\{price * qty}

	Subtotal  $%5.2f\{price * qty}
	Tax       $%5.2f\{price * qty * tax}
	Total     $%5.2f\{price * qty * (1.0 + tax)}
Desc        Unit      Qty   Amount
hammer      $ 7.88      3   $23.64

Subtotal  $23.64
Tax       $ 3.55
Total     $27.19

Why strings?

Often, strings are just exchange format, e.g.:

  • start with: String + values

  • validate / sanitize (i.e. parse)

  • dumb down to: String 🤔

  • parse to: JSONObject, Statement, …

Why the detour?

Custom templating

STR is a singleton instance of
a Processor implementation:

public interface Processor<RESULT, EX> {
	RESULT process(StringTemplate s) throws EX;

RESULT can be of any type!

Custom templating

// prevents SQL injections
Statement query = SQL."""
	SELECT * FROM Person p
	WHERE p.\{property} = '\{value}'

// validates & escapes JSON
JSONObject doc = JSON."""
		"name": "\{name}",
		"year": "\{bday.getYear()}"

Template strings

Preview feature in Java 21! 🙌🏾

Amber endeavors

Pattern matching:

Amber endeavors

Other endeavors and conversations:

Project Amber

  • makes Java more expressive

  • reduces amount of code

  • makes us more productive


JDK 21
  • pattern matching in switch finalizes (JEP 441)

  • record patterns finalize (JEP 440)

  • template strings preview (JEP 430)

  • simplified main previews (JEP 445)


My personal (!) guesses (!!):

  • relaxed this()/super()

  • primitive types in patterns

  • more deconstruction

  • multi-file source launcher

Deeper Dives

Project Panama

Interconnecting JVM and native code



  • vector API

  • foreign memory API

  • foreign function API


Given two float arrays a and b,
compute c = - (a² + b²):

// a, b, c have same length
void compute(float[] a, float[] b, float[] c) {
	for (int i = 0; i < a.length; i++) {
		c[i] = (a[i] * a[i] + b[i] * b[i]) * -1.0f;


Vectorization - modern CPUs:

  • have multi-word registers (e.g. 512 bit)

  • can store several numbers (e.g. 16 float​s)

  • can execute several computations at once

single instruction, multiple data (SIMD)

Just-in-time compiler tries to vectorize loops.

Works but isn’t reliable.

Vector API

static final VectorSpecies<Float> VS =

// a, b, c length is multiple of vector length
void compute(float[] a, float[] b, float[] c) {
	int upperBound = VS.loopBound(a.length);
	for (i = 0; i < upperBound; i += VS.length()) {
		var va = FloatVector.fromArray(VS, a, i);
		var vb = FloatVector.fromArray(VS, b, i);
		var vc = va.mul(va)
		vc.intoArray(c, i);

Vector API


  • clear and concise API (given the requirements)

  • platform agnostic

  • reliable run-time compilation and performance

  • graceful degradation

Foreign memory

Storing data off-heap is tough:

  • ByteBuffer is limited (2GB) and inefficient

  • Unsafe is…​ unsafe and not supported

Foreign-memory API

Safe and performant foreign-memory API:

  • control (de)allocation:
    Arena, MemorySegment, SegmentAllocator

  • to access/manipulate: MemoryLayout, VarHandle

Foreign functions

JNI isn’t ideal:

  • involves several tedious artifacts (header file, impl, …​)

  • can only interoperate with languages that align
    with OS/architecture the JVM was built for

  • doesn’t reconcile Java/C type systems

Foreign-function API

Streamlined tooling/API for foreign functions
based on method handles:

  • jextract: generates method handles from header file

  • classes to call foreign functions
    Linker, FunctionDescriptor, SymbolLookup

Project Panama

  • connects Java with the native world

  • offers safe, detailed, and performant APIs


JDK 21
  • foreign APIs in 3rd preview (JEP 442)

  • vector API in 6th incubation (JEP 448)

Vector API needs to wait for Valhalla’s
primitive types and universal generics.


My personal (!) guess (!!):

  • foreign APIs finalize in 2024

Deeper Dives

Deeper Dives

Project Valhalla

Advanced Java VM and Language feature candidates



Java has a split type system:

  • primitives

  • classes

We can only create classes, but:

  • have identity

  • have references


All classes come with identity:

  • extra memory for header

  • mutability

  • locking, synchronization, etc.

But not all custom types need that!


All class instances come as references:

  • memory access indirection

  • nullability

But not all custom types need that!

Project Valhalla

Valhalla’s goals is to unify the type system:

  • value types (disavow identity)

  • null-restriction + implicit constructors
    (disavow identity + references)

  • universal generics (ArrayList<int>)

  • specialized generics (backed by int[])

Value types

value class RationalNumber {
	private long nominator;
	private long denominator;

	// constructor, etc.

Codes (almost) like a class - exceptions:

  • class and fields are implcitly final

  • superclasses are limited

Value type behavior

No identity:

  • some runtime operations throw exceptions

  • "identity" check == compares by state

  • null is default value


  • guaranteed immutability

  • more expressiveness

  • more optimizations

Migration to value types

The JDK (as well as other libraries) has many value-based classes, such as Optional and LocalDateTime. […​] We plan to migrate many value-based classes in the JDK to value classes.

Getting rid of references

In general, value types have references:

  • allow null

  • prevent flattening

How do we get rid of them?


No references = no null!

⇝ Restrict variables to non-null values:

// number can't be null
ComplexNumber! number = // ...



A variable with a null-restricted type prevents attempts to set the variable to null. Details of this behavior are described in the referenced JEP.

Let’s follow that reference!

null restricted jep


JEP 401 (continued):

The details of general-purpose null-restricted types are still under development. The most relevant feature for this JEP is that the type of a variable or method return may use a ! suffix to indicate that it does not store null. This is enforced with runtime checks.



Variable can’t be null:

ComplexNumber! number = // ...

But can ComplexNumber cope?

Default instances

The type needs a default instance:

  • implicit constructor

  • without code

Implicit constructor

value class ComplexNumber {
	private double real;
	private double imaginary;

	// implicitly sets all fields to default values
	public implicit ComplexNumber();

	public ComplexNumber(double r, double i) {
		// ...

	// etc.


No references

The just-in-time compiler can
inline/flatten variables …

  • of a value type

  • with implicit constructor

  • that are null-restricted

Performance comparable to today’s primitives! 🚀

Emergent performance

Don’t create a type in order to get performance.


  • "Is the type value-ish?" ⇝ value type

  • "Is all-fields-default usable?" ⇝ implicit constructor

  • "Is no null needed?" ⇝ restrict nullness

Performance emerges from domain decisions!

Universal generics

When everybody creates their own value classes,
boxing becomes omni-present and very painful!

Universal generics allow value classes
as type parameters:

List<long> ids = new ArrayList<>();
List<RationalNumber> numbers = new ArrayList<>();

Specialized generics

Healing the rift in the type system is great!

But if ArrayList<int> is backed by Object[],
it will still be avoided in many cases.

Specialized generics will fix that:
Generics over primitives will avoid references!

Project Valhalla

Value types, implicit constructors, null-restriction
plus universal and specialized generics:

  • fewer trade-offs between
    design and performance

  • no more manual specializations

  • better performance

  • can express design more clearly

  • more robust APIs

Makes Java more expressive and performant.



At most one more iteration.

— Brian Goetz

Deeper Dives

Deeper Dives

Ad break

There’s much more going on!


Lots of API additions and changes:

  • sequenced collections ㉑ (JEP 431)

  • IP address resolution SPI ⑱ (JEP 418)

  • new random generator API ⑰ (JEP 356)

  • Unix domain sockets ⑯ (JEP 380)

As well as lots of small additions to:
String, Stream, Math, CompletableFuture, regex, HTTP/2 API




Plus continuous GC and
performance improvements.


Cleaning house

Deprecations (for removal):

Cleaning house

Already removed:


To ease migrations:

  • stick to supported APIs

  • stick to standardized behavior

  • stick to well-maintained projects

  • keep dependencies and tools up to date

  • stay ahead of removals (jdeprscan)

  • build on each release (including EA)

Then you, too, can enjoy these projects ASAP!


  • Java 11+ overtook Java 8

  • adoption of 17 (from 11) looks good

  • lots of excitement for Java 21

Project Loom

JVM features and APIs for supporting easy-to-use, high-throughput, lightweight concurrency and new programming models



Imagine a hypothetical HTTP request:

  1. interpret request

  2. query database (blocks)

  3. process data for response

Resource utilization:

  • good for 1. and 3.

  • really bad for 2.

How to implement that request?


Align application’s unit of concurrency (request)
with Java’s unit of concurrency (thread):

  • use thread per request

  • simple to write, debug, profile

  • blocks threads on certain calls

  • limited number of platform threads
    ⇝ bad resource utilization
    ⇝ low throughput


Only use threads for actual computations:

  • use non-blocking APIs
    (with futures / reactive streams)

  • harder to write, challenging to debug/profile

  • incompatible with synchronous code

  • shares platform threads
    ⇝ great resource utilization
    ⇝ high throughput


Resolve the conflict between:

  • simplicity

  • throughput

Enter virtual threads!

A virtual thread:

  • is a regular Thread

  • low memory footprint ([k]bytes)

  • small switching cost

  • scheduled by the Java runtime

  • requires no OS thread when waiting

Virtual thread management

The runtime manages virtual threads:

  • runs them on a pool of carrier threads

  • makes them yield on blocking calls
    (frees the carrier thread!)

  • continues them when calls return

Virtual thread example

Remember the hypothetical request:

  1. interpret request

  2. query database (blocks)

  3. process data for response

In a virtual thread:

  • runtime submits task to carrier thread pool

  • when 2. blocks, virtual thread yields

  • runtime hands carrier thread back to pool

  • when 2. unblocks, runtime resubmits task

  • virtual thread continues with 3.


try (var executor = Executors
		.newVirtualThreadPerTaskExecutor()) {
		.range(0, 1_000_000)
		.forEach(number -> {
			executor.submit(() -> {
				return number;
} // executor.close() is called implicitly, and waits


void handle(Request request, Response response)
		throws InterruptedException {
	try (var executor = Executors
			.newVirtualThreadPerTaskExecutor()) {
		var futureA = executor.submit(this::taskA);
		var futureB = executor.submit(this::taskB);
		response.send(futureA.get() + futureB.get());
	} catch (ExecutionException ex) {;


Virtual threads aren’t "faster threads":
Each task takes the same time (same latency).

So why bother?

Parallelism vs concurrency


Task origin






Resource use







CPU cores


# of threads

# of cores

# of tasks


When workload is not CPU-bound:

  • start waiting as early as possible

  • for as many tasks as possible

⇝ Virtual threads increase throughput:

  • when number of concurrent tasks is high

  • when workload is not CPU-bound

Use Cases

Virtual threads are cheap and plentiful:

  • no pooling necessary

  • allows thread per task

  • allows liberal creation
    of threads for subtasks

⇝ Enables new concurrency programming models.

Structured concurrency

Structured programming:

  • prescribes single entry point
    and clearly defined exit points

  • influenced languages and runtimes

Simlarly, structured concurrency prescribes:

When the flow of execution splits into multiple concurrent flows, they rejoin in the same code block.

Structured concurrency

When the flow of execution splits into multiple concurrent flows, they rejoin in the same code block.

⇝ Threads are short-lived:

  • start when task begins

  • end on completion

⇝ Enables parent-child/sibling relationships
and logical grouping of threads.

Unstructured concurrency

void handle(Request request, Response response)
		throws InterruptedException {
	try (var executor = Executors
			.newVirtualThreadPerTaskExecutor()) {
		// what's the relationship between
		// this and the two spawned threads?
		// what happens when one of them fails?
		var futureA = executor.submit(this::taskA);
		var futureB = executor.submit(this::taskB);
		// what if we only need the faster one?
		response.send(futureA.get() + futureB.get());
	} catch (ExecutionException ex) {;

Structured concurrency

void handle(Request request, Response response)
		throws InterruptedException {
	// define explicit success/error handling
	try (var scope = new StructuredTaskScope
			.ShutdownOnFailure()) {
		var futureA = scope.fork(() -> doA(request));
		var futureB = scope.fork(() -> doB(request));
		// wait explicitly until success criteria met

		response.send(futureA.get() + futureB.get());
	} catch (ExecutionException ex) {;

Structured concurrency

  • forked tasks are children of the scope

  • creates relationship between threads

  • success/failure policy can be defined
    across all children

Project Loom

Virtual threads:

  • code is simple to write, debug, profile

  • high throughput

  • new programing model

Structured concurrency:

  • clearer concurrency code

  • simpler failure/success policies

  • better debugging


JDK 21
  • virtual threads finalize (JEP 444)

  • structured concurrency previews (JEP 453)

  • scoped values preview (JEP 446)


My personal (!) guesses (!!):

  • structured concurrency and
    scoped vlaues finalize

  • maybe more structured concurrency APIs

Deeper Dives

So long…​

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