In this tutorial, I will talk about the JDK 11 product changes. Then I will dive into several API changes with Java examples. Finally I will show the new Single-File Launcher, which executes a Java source file without going through the compile processing.

1. Java 11 New Features – Introduction

Oracle JDK was free and richer than theOpenJDK prior toversion 11 that was released on September 25, 2018. Oracle has shipped its OpenJDK athttp://jdk.java.net/ and licensed it under GPL+CE since 2017.Oracle commercial JDK and OpenJDK are almost identical in version 11. Oracle commercial JDK is not free to use in production since version 11. Clickhere for more details about Oracle release cycle and the free-support expiration date.

There are other OpenJDK providers, such as IBM and RedHat. Clickhere for more details about OpenJDK providers comparison.

Java 11 includes lots of bug fixes and seventeen JDK Enhancement Proposals (JEPs). Here are the list of JEPs:

• 181: Nest-Based Access Control
• 309: Dynamic Class-File constants
• 315: Improve Aarch6 Intrinsic
• 318: Epsilon: A no-op Garbage collector (Experimental)
• 320: Remove the Java EE and CORBA Modules
• 321: HTTP Client (Standard)
• 323: Local-Variable Syntax for Lambda Parameters
• 324: Key Agreement with Curve25519 and Curve448
• 327: Unicode 10
• 328: Flight Recorder
• 329: ChaCha20 and Poly1305 Cryptographic Algorithms
• 330: Launch Single-File Source Code Programs
• 331: Low-Overhead Heap Profiling
• 332: Transport Layer Security (TLS) 1.3
• 333: ZGC: A Scalable Low-Latency Garbage Collector (Experimental)
• 336: Deprecate the Pack200 Tools and API

In this tutorial, I will use Oracle OpenJDK 11 to demonstrate the following API changes:

• Thejava.lang.String class has six new methods.
• Thejava.nio.file.Files class has four new static methods.
• Thejava.util.function.Predicate has one new method.
• The newjava.net.http module supportshttpclient.
• Single file launcher executes the source code without compiling first.

2. Install Oracle OpenJDK 11

In this step, I will install Oracle OpenJDK 11 in my Windows 10 PC. Oracle outlines the installation stepshere. Here are my steps:

Downloadhttp://jdk.java.net/11/. Extract the zip file into a folder. Mine is atC:\MaryZheng\DevTools\Java\OpenJDK11\jdk-11.0.2

Set up the environment variables forJAVA_HOME andPATH.

set environment variables

C:\MaryZheng\DevTools\Java>set JAVA_HOME=C:\MaryZheng\DevTools\Java\OpenJDK11\jdk-11.0.2C:\MaryZheng\DevTools\Java>set PATH=%JAVA_HOME%\bin;%PATH%C:\MaryZheng\DevTools\Java>where javaC:\MaryZheng\DevTools\Java\OpenJDK11\jdk-11.0.2\bin\java.exe

Verify that JDK11 is installed correctly by executing the commandjava -version

java -version

C:\MaryZheng\DevTools\Java>java -versionopenjdk version "11.0.2" 2019-01-15OpenJDK Runtime Environment 18.9 (build 11.0.2+9)OpenJDK 64-Bit Server VM 18.9 (build 11.0.2+9, mixed mode)

3. Technologies Used

The example code in this article was built and run using:

• Java 11
• Maven 3.6.0
• Eclipse
• JUnit 4.12

I will create a simple Maven project.Pom.xml includes a Junit dependency.

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd"><modelVersion>4.0.0</modelVersion><groupId>jdk11-demo</groupId><artifactId>jdk11-demo</artifactId><version>0.0.1-SNAPSHOT</version><build><sourceDirectory>src</sourceDirectory><plugins><plugin><artifactId>maven-compiler-plugin</artifactId><version>3.8.0</version><configuration><release>11</release></configuration></plugin></plugins></build><dependencies><dependency><groupId>junit</groupId><artifactId>junit</artifactId><version>4.12</version></dependency></dependencies></project>

4. Changes at java.lang.String

JDK 11 enhances thejava.lang.String class with six new methods:

• boolean isBlank() – returns true if the string is empty or contains only white-spaces.
• Stream <String> lines() – returns a stream of lines extracted from this string, separated by line terminators.
• String repeat​(int count) – returns a string whose value is the concatenation of this string’s repeated count times.
• String strip() – returns a string whose value is this string, with all leading and trailing white-spaces removed.
• String stripLeading() – returns a string whose value is this string, with all leading white-spaces removed.
• String stripTrailing() – returns a string whose value is this string, with all trailing white-spaces removed.

In this step, I will create aStringTest.java class to demonstrate these new methods. Clickhere for a very detailed example.

StringTest.java

package org.jcg.zheng;import static org.junit.Assert.assertEquals;import static org.junit.Assert.assertTrue;import java.util.List;import java.util.stream.Collectors;import org.junit.Test;public class StringTest {    private static final char UNICODE_SPACE_VER52 = '\u2000';    private static final char ASCII_UTF8 = '\u0020';    @Test    public void test_repeat() {        String test = new String("Test");        String longString = test.repeat(10);        assertEquals("TestTestTestTestTestTestTestTestTestTest", longString);    }    @Test    public void test_lines() {        String multipleLinesString = "First line.\nSecond line.\nThird line.\n";        List<String> lines = multipleLinesString.lines().collect(Collectors.toList());        assertEquals("First line.", lines.get(0));        assertEquals("Second line.", lines.get(1));        assertEquals("Third line.", lines.get(2));    }    @Test    public void test_stripLeading() {        String hasLeadingWhiteSpace = " Test  ";        String clearedTest = hasLeadingWhiteSpace.stripLeading();        assertEquals("Test  ", clearedTest);    }    @Test    public void test_stripTrailing() {        String hasLeadingWhiteSpace = " Test  ";        String clearedTest = hasLeadingWhiteSpace.stripTrailing();        assertEquals(" Test", clearedTest);    }    @Test    public void test_strip() {        String hasLeadingWhiteSpace = " Test\t\n  ";        String clearedTest = hasLeadingWhiteSpace.strip();        assertEquals("Test", clearedTest);    }    @Test    public void test_trim() {        String hasLeadingWhiteSpace = " Test\t\n  ";        String clearedTest = hasLeadingWhiteSpace.trim();        assertEquals("Test", clearedTest);    }    @Test    public void trim_vs_strip() {        String testStr = UNICODE_SPACE_VER52 + "abc" + UNICODE_SPACE_VER52;        assertTrue(Character.isWhitespace(UNICODE_SPACE_VER52));        assertEquals(UNICODE_SPACE_VER52 + "abc" + UNICODE_SPACE_VER52, testStr.trim());        // Strip is Unicode-aware        assertEquals("abc", testStr.strip());        testStr = ASCII_UTF8 + "abc" + ASCII_UTF8;        assertTrue(Character.isWhitespace(ASCII_UTF8));        assertEquals("abc", testStr.trim());        assertEquals("abc", testStr.strip());        testStr = '\u001F' + "abc" + '\u001F';        assertTrue(Character.isWhitespace('\u001F'));        assertEquals("abc", testStr.trim());        assertEquals("abc", testStr.strip());    }    @Test    public void test_isBlank() {        assertTrue("".isBlank());        assertTrue(System.getProperty("line.separator").isBlank());        assertTrue("\t".isBlank());        assertTrue("    ".isBlank());        assertTrue("\t\n    ".isBlank());    }}

Note: The existingtrim() method provides the same functions as thestrip() method with the only difference being the white-space definition. In thetrim() method, the white-space is defined as any character whosecodepoint is less than or equal to\u0020. In thestrip() method, the white-space is defined by the staticCharacter.isWhitespace method.

5. Changes at java.nio.file.Files

Java 11 enhancesjava.nio.file.Files by adding four new static methods to read string from a file and write string into a file directly:

• static String readString(Path path) – reads contents from a file into a string, decoding from bytes to characters using theUTF-8 charset.
• static String readString(Path path, Charset cs) – reads characters from a file into a string, decoding from bytes to characters using the specifiedcharset.
• static Path writeString(Path path, CharSequence csq, OpenOption… options) – writes aCharSequence to a file
• static Path writeString(Path path, CharSequence csq, Charset cs, OpenOption… options) – writes aCharSequence to a file with the specifiedcharset.

In this step, I will create aFilesTest.java to show you how to use these methods to read string from a file and write string to a file.

FilesTest.java

package org.jcg.zheng;import static org.junit.Assert.assertEquals;import java.io.IOException;import java.nio.charset.Charset;import java.nio.file.Files;import java.nio.file.Path;import org.junit.Test;public class FilesTest {    @Test    public void writeString_readString() {        try {            Path localFile = Path.of("C:\\MaryZheng\\Temp\\test.txt");            String sampleString = "Some example of text";            Files.writeString(localFile, sampleString);            String readData = Files.readString(localFile);            assertEquals(sampleString, readData);        } catch (IOException e) {            e.printStackTrace();        }    }    @Test    public void writeString_readString_utf8() {        try {            String sampleString = "Some example of text";            Files.writeString(Path.of("test.txt"), sampleString, Charset.forName("UTF-8"));            String readData = Files.readString(Path.of("test.txt"));            assertEquals(sampleString, readData);        } catch (IOException e) {            e.printStackTrace();        }    }}

6. Change at java.util.Predicate

JDK11 enhancesjava.util.function.Predicate with a staticnot() method.

static <T> Predicate<T> not​(Predicate<? super T> target) – returns a predicate that is the negation of the supplied predicate.

In this step, I will create aPredicateTest.java to show how to use thenot method to filter out an empty name from a list of names.

PredicateTest.java

package org.jcg.zheng;import static org.junit.Assert.assertEquals;import java.util.List;import java.util.function.Predicate;import java.util.stream.Collectors;import java.util.stream.Stream;import org.junit.Test;public class PredicateTest {    @Test    public void test_Predicate_Not() {        String[] names = { "TEST", "MARY", " ", "" };        List loweCaseList = Stream.of(names).filter(Predicate.not(String::isBlank))                .collect(Collectors.toList());        assertEquals(2, loweCaseList.size());    }}

7. New HttpClient Module

JDK 11 provides a new module –java.net.http. It supports both HTTP/1.1 and HTTP/2 and replaces the legacyHttpUrlConnection class. It includes several new classes:

• HttpClient – sends requests and receive responses. It uses a builder to create an instance.
• HttpRequest – encapsulates an HTTP request. A request is constructed using a builder.HttpRequest.BodyPublisher handles when a request has a body.
• HttpResponse – encapsulates an HTTP response.HttpResponse.BodyHandler handles the response body.

In this step, I will create anHttpClientTest.java to show how to invokeRestful services to create, read, update, and delete a user.

HttpClientTest.java

package org.jcg.zheng;import java.net.URI;import java.net.http.HttpClient;import java.net.http.HttpRequest;import java.net.http.HttpRequest.BodyPublishers;import java.net.http.HttpResponse;import java.net.http.HttpResponse.BodyHandlers;import org.junit.Before;import org.junit.Test;public class HttpClientTest {    private HttpClient client;    String serviceUri;    @Before    public void setup() {        client = HttpClient.newHttpClient();// default to HTTP_2        serviceUri = "https://reqres.in/api/users";    }    @Test    public void get_ofString() {        String getUrl = serviceUri + "/2";        HttpRequest request = HttpRequest.newBuilder().uri(URI.create(getUrl)).build();        HttpResponse response;        try {            response = client.send(request, BodyHandlers.ofString());            System.out.println("Response" + response.body());        } catch (Exception e) {            e.printStackTrace();        }    }    @Test    public void put_ofString() {        String putUrl = serviceUri + "/2";        String upUsdateerString = "{\"name\": \"Mary\",  \"job\": \"leader\"}";        HttpRequest request = HttpRequest.newBuilder().uri(URI.create(putUrl))                .PUT(BodyPublishers.ofString(upUsdateerString)).build();        HttpResponse response;        try {            response = client.send(request, BodyHandlers.ofString());            System.out.println("Response" + response.body());        } catch (Exception e) {            e.printStackTrace();        }    }    @Test    public void post_discarding() {        String newUserString = "{\"name\": \"Mary\",  \"job\": \"leader\"}";        HttpRequest request = HttpRequest.newBuilder().uri(URI.create(serviceUri))                .POST(BodyPublishers.ofString(newUserString)).build();        try {            HttpResponse response = client.send(request, BodyHandlers.discarding());            System.out.println("Response" + response.statusCode());        } catch (Exception e) {            e.printStackTrace();        }    }    @Test    public void delete_ofString() {        String deleteUrl = serviceUri + "/2";        HttpRequest request = HttpRequest.newBuilder().uri(URI.create(deleteUrl)).DELETE().build();        try {            HttpResponse response = client.send(request, BodyHandlers.discarding());            System.out.println("Response" + response.statusCode());        } catch (Exception e) {            e.printStackTrace();        }    }}

8. New Single-File Launcher

JDK11’s new single-file launcher allows executing Java source codes directly using thejava interpreter. The source code is compiled in memory and then executed by the interpreter. The limitation is that all the classes have to be defined in the same file.

In this step, I will create a java source file which has apublic static main method and prints out a “hello world” message.

8.1 A Source File

SingleFileLauncher .java

public class SingleFileLauncher {    public static void main(String[] args) {        System.out.println("Hello World!!!");    }}

8.2 Demo with javac and java

Prior to Java 11, you need to do two steps:

• Runjavac.exe to generate the byte-code class files
• Executejava with a class name.

javac command example

C:\MaryZheng\Workspaces\jdk11-demo\src\main\java>javac SingleFileLauncher.javaC:\MaryZheng\Workspaces\jdk11-demo\src\main\java>dir Volume in drive C is OSDisk Volume Serial Number is 528C-6C8F Directory of C:\MaryZheng\Workspaces\jdk11-demo\src\main\java03/10/2019  01:04 PM    <DIR>          .03/10/2019  01:04 PM    <DIR>          ..02/18/2019  01:52 PM    <DIR>          org03/10/2019  01:04 PM               444 SingleFileLauncher.class03/10/2019  12:44 PM               138 SingleFileLauncher.java               2 File(s)            582 bytes               3 Dir(s)  25,755,234,304 bytes freeC:\MaryZheng\Workspaces\jdk11-demo\src\main\java>

java command example

C:\MaryZheng\Workspaces\jdk11-demo\src\main\java>java SingleFileLauncherHello World!!!C:\MaryZheng\Workspaces\jdk11-demo\src\main\java>

8.3 Demo with Single-File Launcher

In Java 11, you can runjava with a java source file name directly.

java ${fileName.java}

C:\MaryZheng\Workspaces\jdk11-demo>java src\main\java\SingleFileLauncher.javaHello World!!!C:\MaryZheng\Workspaces\jdk11-demo>

Note: The java source file name follows the file format not the java package format.

9. Summary

In this tutorial, I demonstrated five API changes in Java 11:

• Thejava.lang.String class – six new methods
• Thejava.nio.file.Files class – four new static methods
• Thejava.util.function.Predicate – one new method
• The newjava.net.http module –httpclient
• Single file launcher – execute source code without compiling first

But there are more changes in Java 11 than the ones demonstrated here. Please visitOracle web site for more details.

10. Download the Source Code

This was a Java 11 new features tutorial.

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