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1. Overview

Oracle released Java 11 in September 2018, only 6 months after its predecessor, version 10.

Java 11 is the first long-term support (LTS) release after Java 8. Oracle also stopped supporting Java 8 in January 2019. As a consequence, a lot of us will upgrade to Java 11.

In this tutorial, we'll take a look at our options for choosing a Java 11 JDK. Then we'll explore new features, removed features, and performance enhancements introduced in Java 11.

Further reading:

Java 11 String API Additions

Learn about additions to the String API in Java 11.

Java 11 Local Variable Syntax for Lambda Parameters

Learn how to use var syntax with lambda expressions in Java 11

Negate a Predicate Method Reference with Java 11

Learn how to negate a predicate method reference with Java 11.

2. Oracle vs. Open JDK

Java 10 was the last free Oracle JDK release that we could use commercially without a license. Starting with Java 11, there's no free long-term support (LTS) from Oracle.

Thankfully, Oracle continues to provide Open JDK releases, which we can download and use without charge.

Besides Oracle, there are other Open JDK providers that we may consider.

3. Developer Features

Let's take a look at changes to the common APIs, as well as a few other features useful for developers.

3.1. New String Methods

Java 11 adds a few new methods to the String class: isBlank, lines, strip, stripLeading, stripTrailing, and repeat.

Let's see how we can make use of the new methods to extract non-blank, stripped lines from a multi-line string:

String multilineString = "Baeldung helps \n \n developers \n explore Java.";
List<String> lines = multilineString.lines()
  .filter(line -> !line.isBlank())
  .map(String::strip)
  .collect(Collectors.toList());
assertThat(lines).containsExactly("Baeldung helps", "developers", "explore Java.");

These methods can reduce the amount of boilerplate involved in manipulating string objects, and save us from having to import libraries.

In the case of the strip methods, they provide similar functionality to the more familiar trim method; however, with finer control and Unicode support.

3.2. New File Methods

Additionally, it's now easier to read and write Strings from files.

We can use the new readString and writeString static methods from the Files class:

Path filePath = Files.writeString(Files.createTempFile(tempDir, "demo", ".txt"), "Sample text");
String fileContent = Files.readString(filePath);
assertThat(fileContent).isEqualTo("Sample text");

3.3. Collection to an Array

The java.util.Collection interface contains a new default toArray method which takes an IntFunction argument.

This makes it easier to create an array of the right type from a collection:

List sampleList = Arrays.asList("Java", "Kotlin");
String[] sampleArray = sampleList.toArray(String[]::new);
assertThat(sampleArray).containsExactly("Java", "Kotlin");

3.4. The Not Predicate Method

A static not method has been added to the Predicate interface. We can use it to negate an existing predicate, much like the negate method:

List<String> sampleList = Arrays.asList("Java", "\n \n", "Kotlin", " ");
List withoutBlanks = sampleList.stream()
  .filter(Predicate.not(String::isBlank))
  .collect(Collectors.toList());
assertThat(withoutBlanks).containsExactly("Java", "Kotlin");

While not(isBlank) reads more naturally than isBlank.negate(), the big advantage is that we can also use not with method references, like not(String:isBlank).

3.5. Local-Variable Syntax for Lambda

Support for using the local variable syntax (var keyword) in lambda parameters was added in Java 11.

We can make use of this feature to apply modifiers to our local variables, like defining a type annotation:

List<String> sampleList = Arrays.asList("Java", "Kotlin");
String resultString = sampleList.stream()
  .map((@Nonnull var x) -> x.toUpperCase())
  .collect(Collectors.joining(", "));
assertThat(resultString).isEqualTo("JAVA, KOTLIN");

3.6. HTTP Client

The new HTTP client from the java.net.http package was introduced in Java 9. It has now become a standard feature in Java 11.

The new HTTP API improves overall performance and provides support for both HTTP/1.1 and HTTP/2:

HttpClient httpClient = HttpClient.newBuilder()
  .version(HttpClient.Version.HTTP_2)
  .connectTimeout(Duration.ofSeconds(20))
  .build();
HttpRequest httpRequest = HttpRequest.newBuilder()
  .GET()
  .uri(URI.create("http://localhost:" + port))
  .build();
HttpResponse httpResponse = httpClient.send(httpRequest, HttpResponse.BodyHandlers.ofString());
assertThat(httpResponse.body()).isEqualTo("Hello from the server!");

3.7. Nest Based Access Control

Java 11 introduces the notion of nestmates and the associated access rules within the JVM.

A nest of classes in Java implies both the outer/main class and all its nested classes:

assertThat(MainClass.class.isNestmateOf(MainClass.NestedClass.class)).isTrue();

Nested classes are linked to the NestMembers attribute, while the outer class is linked to the NestHost attribute:

assertThat(MainClass.NestedClass.class.getNestHost()).isEqualTo(MainClass.class);

JVM access rules allow access to private members between nestmates; however, in previous Java versions, the reflection API denied the same access.

Java 11 fixes this issue and provides means to query the new class file attributes using the reflection API:

Set<String> nestedMembers = Arrays.stream(MainClass.NestedClass.class.getNestMembers())
  .map(Class::getName)
  .collect(Collectors.toSet());
assertThat(nestedMembers).contains(MainClass.class.getName(), MainClass.NestedClass.class.getName());

3.8. Running Java Files

A major change in this version is that we don't need to compile the Java source files with javac explicitly anymore:

$ javac HelloWorld.java
$ java HelloWorld 
Hello Java 8!

Instead, we can directly run the file using the java command:

$ java HelloWorld.java
Hello Java 11!

4. Performance Enhancements

Now let's take a look at a couple of new features whose main purpose is improving performance.

4.1. Dynamic Class-File Constants

Java class-file format is extended to support a new constant-pool form named CONSTANT_Dynamic.

Loading the new constant-pool will delegate creation to a bootstrap method, just as linking an invokedynamic call site delegates linkage to a bootstrap method.

This feature enhances performance and targets language designers and compiler implementors.

4.2. Improved Aarch64 Intrinsics

Java 11 optimizes the existing string and array intrinsics on ARM64 or AArch64 processors. Additionally, new intrinsics are implemented for sin, cos, and log methods of java.lang.Math.

We use an intrinsic function like any other; however, the intrinsic function gets handled in a special way by the compiler. It leverages CPU architecture-specific assembly code to boost performance.

4.3. A No-Op Garbage Collector

A new garbage collector called Epsilon is available for use in Java 11 as an experimental feature.

It's called a No-Op (no operations) because it allocates memory but does not actually collect any garbage. Thus, Epsilon is applicable for simulating out of memory errors.

Obviously Epsilon won't be suitable for a typical production Java application; however, there are a few specific use-cases where it could be useful:

  • Performance testing
  • Memory pressure testing
  • VM interface testing and
  • Extremely short-lived jobs

In order to enable it, use the -XX:+UnlockExperimentalVMOptions -XX:+UseEpsilonGC flag.

4.4. Flight Recorder

Java Flight Recorder (JFR) is now open-source in Open JDK, whereas it used to be a commercial product in Oracle JDK. JFR is a profiling tool that we can use to gather diagnostics and profiling data from a running Java application.

To start a 120 seconds JFR recording, we can use the following parameter:

-XX:StartFlightRecording=duration=120s,settings=profile,filename=java-demo-app.jfr

We can use JFR in production since its performance overhead is usually below 1%. Once the time elapses, we can access the recorded data saved in a JFR file; however, in order to analyze and visualize the data, we need to make use of another tool called JDK Mission Control (JMC).

5. Removed and Deprecated Modules

As Java evolves, we can no longer use any of its removed features and should stop using any deprecated features. Let's take a quick look at the most notable ones.

5.1. Java EE and CORBA

Standalone versions of the Java EE technologies are available on third-party sites; therefore, there is no need for Java SE to include them.

Java 9 already deprecated selected Java EE and CORBA modules. In release 11, it has now completely removed:

  • Java API for XML-Based Web Services (java.xml.ws)
  • Java Architecture for XML Binding (java.xml.bind)
  • JavaBeans Activation Framework (java.activation)
  • Common Annotations (java.xml.ws.annotation)
  • Common Object Request Broker Architecture (java.corba)
  • JavaTransaction API (java.transaction)

5.2. JMC and JavaFX

JDK Mission Control (JMC) is no longer included in the JDK. A standalone version of JMC is now available as a separate download.

The same is true for JavaFX modules; JavaFX will be available as a separate set of modules outside of the JDK.

5.3. Deprecated Modules

Furthermore, Java 11 deprecated the following modules:

  • Nashorn JavaScript engine, including the JJS tool
  • Pack200 compression scheme for JAR files

6. Miscellaneous Changes

Java 11 introduced a few more changes that are important to mention:

  • New ChaCha20 and ChaCha20-Poly1305 cipher implementations replace the insecure RC4 stream cipher
  • Support for cryptographic key agreement with Curve25519 and Curve448 replace the existing ECDH scheme
  • Upgraded Transport Layer Security (TLS) to version 1.3 brings security and performance improvements
  • Introduced a low latency garbage collector, ZGC, as an experimental feature with low pause times
  • Support for Unicode 10 brings more characters, symbols, and emojis

7. Conclusion

In this article, we explored some new features of Java 11.

We covered the differences between Oracle and Open JDK. We also reviewed API changes, as well as other useful development features, performance enhancements, and removed or deprecated modules.

As always, the source code is available over on GitHub.

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