The road from Java 8 to Java 11

dfa@aman:~ $ cat Hello.java (1)
public class Hello { (1)
        public static void main(String[] args) {
                System.out.println("hello world!");
        }
}
dfa@aman:~ $ javac Hello.java (2)
dfa@aman:~ $ java Hello (2)
hello world!

dfa@aman:~ $ cat demo.java (1)
public class Hello { (1)
        public static void main(String[] args) {
                System.out.println("hello world!");
        }
}
dfa@aman:~ $ java hello.java (2)
hello world!

dfa@aman:~ $ docker run --rm -p 80:80 kennethreitz/httpbin
[2018-09-29 10:04:20 +0000] [1] [INFO] Starting gunicorn 19.9.0
[2018-09-29 10:04:20 +0000] [1] [INFO] Listening at: http://0.0.0.0:80 (1)
[2018-09-29 10:04:20 +0000] [1] [INFO] Using worker: gevent
[2018-09-29 10:04:20 +0000] [9] [INFO] Booting worker with pid: 9

dfa@aman:~ $ curl localhost/user-agent
{
  "user-agent": "curl/7.54.0"
}

import java.net.URI;
import java.net.http.*;
import java.time.Duration;

public class HttpClientDemo {
        public static void main(String[] args) throws Exception {
                if (args.length != 1) {
                        System.err.println("missing URL argument");
                        System.exit(1);
                }
                URI uri = URI.create(args[0]);
                HttpClient client = HttpClient.newBuilder()
                        .version(HttpClient.Version.HTTP_2)
                        .build();
                HttpRequest request = HttpRequest.newBuilder()
                        .uri(uri)
                        .timeout(Duration.ofSeconds(1))
                        .build();
                HttpResponse<String> response = client.send(request, HttpResponse.BodyHandlers.ofString());
                System.out.print(response.body());
        }
}

dfa@aman:~ $ java java11_http_client.java http://localhost/user-agent
{
  "user-agent": "Java-http-client/11"
}

dfa@aman:~ $ java java11_http_client.java http://localhost/delay/2
Exception in thread "main" java.net.http.HttpTimeoutException: request timed out (1)
	at java.net.http/jdk.internal.net.http.HttpClientImpl.send(HttpClientImpl.java:559)
	at java.net.http/jdk.internal.net.http.HttpClientFacade.send(HttpClientFacade.java:119)
	at HttpClientDemo.main(java11_http_client.java:19)

(var x, var y) -> x.process(y)

(x, y) -> x.process(y)

Optional<String> featureToggle = ...;
if (featureToggle.isEmpty()) {
        logger.warn("feature 'xxx' disabled");
}

jshell> int[] a = { 1 }
a ==> int[1] { 1 }

jshell> a[4]
|  Exception java.lang.ArrayIndexOutOfBoundsException: Index 4 out of bounds for length 1
|        at (#2:1)

jshell> int[] a = { 1 }
a ==> int[1] { 1 }

jshell> a[4]
|  java.lang.ArrayIndexOutOfBoundsException thrown: 4
|        at (#4:1)

String d = Character.toString(100)
assert d.equals("d")

String a = Character.toString(65);
assert a.equals("A")

jshell> "a\nb\nc\n".lines().map(String::toUpperCase).toArray()
$1 ==> Object[2] { "A", "B", "C }

jshell> "ab".repeat(5) (1)
$1 ==> "ababababab"

jshell> "ab".repeat(1) (2)
$2 ==> "ab"

jshell> "ab".repeat(0) (3)
$3 ==> ""

jshell> "ab".repeat(-1) (4)
|  Exception java.lang.IllegalArgumentException: count is negative: -1
|        at String.repeat (String.java:3149)
|        at (#1:1)

jshell> "ab".repeat(Integer.MAX_VALUE) (5)
|  Exception java.lang.OutOfMemoryError: Repeating 4 bytes String 2147483647 times will produce a String exceeding maximum size.
|        at String.repeat (String.java:3164)
|        at (#2:1)

jshell> var halfSpace = "\u0020"
halfSpace ==> " "

jshell> var fullSpace = "\u3000"
fullSpace ==> "　"

jshell> halfSpace.trim().isEmpty()
$1 ==> true (1)

jshell> fullSpace.trim().isEmpty()
$2 ==> false (2)

boolean blank = string.codePoints().allMatch(Character::isWhitespace);

jshell> var halfSpace = "\u0020"
halfSpace ==> " "

jshell> var fullSpace = "\u3000"
fullSpace ==> "　"

jshell> halfSpace.repeat(10).isBlank()
$1 ==> true

jshell> fullSpace.repeat(10).isBlank()
$2 ==> true

jshell> var nonBreakingSpace = "\u00A0"
nonBreakingSpace ==> " "

jshell> nonBreakingSpace.isBlank()
$1 ==> false

jshell> var halfSpace = "\u0020"
halfSpace ==> " "

jshell> halfSpace.trim()
$2 ==> ""

jshell> var fullSpace = "\u3000"
$3 ==> " "

jshell> fullSpace.trim()
$4 ==> " " (1)

jshell> fullSpace.strip()
$5 ==> "" (2)

jshell> var text = fullSpace + "foo bar" + fullSpace
text ==> "　foo bar　"

jshell> text.stripTrailing()
$7 ==> "　foo bar"

jshell> text.stripLeading()
$8 ==> "foo bar　"

jshell> var builder = new StringBuilder("aaa");
builder ==> aaa

jshell> var buffer = new StringBuffer("aaa");
buffer ==> aaa

jshell> var string = "aaa";
string ==> "aaa"

jshell> CharSequence.compare(builder, buffer); (1)
$1 ==> 0

jshell> CharSequence.compare(string, buffer); (2)
$2 ==> 0

String content = Files.readString(Path.of("main.adoc"), StandardCharsets.UTF_8);

jshell> Path.of("dir", "subdir", "file")
$2 ==> dir/subdir/file

jshell> Path.of()
|  Error:
|  no suitable method found for of(no arguments)
|      method java.nio.file.Path.of(java.lang.String,java.lang.String...) is not applicable
|        (actual and formal argument lists differ in length)
|      method java.nio.file.Path.of(java.net.URI) is not applicable
|        (actual and formal argument lists differ in length)
|  Path.of()
|  ^-----^

public static Path of(String first, String... more) {
    ...
}

HashMap<String, String> a = new HashMap<>();
var b = new HashMap<String, String>();
assert a.equals(b);

Map<String, Integer> map = Map.of("a", 1, "b", 2); (1)
for (Map.Entry<String, Integer> entry : map.entrySet()) { (1)
    System.out.println(entry);
}

var map2 = Map.copyOf(map); (2)
for (var entry : map2.entrySet()) { (2)
    System.out.println(entry);
}

jshell> var var = 1 (1)
var ==> 1

jshell> class var { } (2)
|  Error:
|  'var' not allowed here
|    as of release 10, 'var' is a restricted local variable type and cannot be used for type declarations
|  class var { }

var a = new Object() {
   void m() {
   }
};
a.m(); (1)

dfa@aman ~ $ docker container run -it --rm --cpus 1 openjdk:9-jdk-slim (1)
Sep 29, 2018 7:56:31 AM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 9.0.4
|  For an introduction type: /help intro

jshell> Runtime.getRuntime().availableProcessors()
$1 ==> 4 (2)

dfa@aman:~ $ docker container run -it --rm --cpus 1 openjdk:10-jdk-slim (1)
Sep 29, 2018 8:11:29 AM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10.0.2
|  For an introduction type: /help intro

jshell> Runtime.getRuntime().availableProcessors()
$1 ==> 1 (2)

dfa@aman:~ $ docker container run -it --rm --cpuset-cpus="1,2"  openjdk:10-jdk-slim
Sep 29, 2018 8:14:53 AM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10.0.2
|  For an introduction type: /help intro

jshell> Runtime.getRuntime().availableProcessors()
$1 ==> 2

dfa@aman:~ $ docker container run -it --rm openjdk:10-jdk-slim
Sep 29, 2018 8:20:47 AM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10.0.2
|  For an introduction type: /help intro

jshell> Runtime.getRuntime().maxMemory() / 1024 / 1024
$2 ==> 500 (1)

dfa@aman:~ $ docker container run -it --rm --memory 512M openjdk:10-jdk-slim (1)
Sep 29, 2018 8:25:12 AM java.util.prefs.FileSystemPreferences$1 run
INFO: Created user preferences directory.
|  Welcome to JShell -- Version 10.0.2
|  For an introduction type: /help intro

jshell> Runtime.getRuntime().maxMemory() / 1024 / 1024
$1 ==> 123 (2)

{@summary This is the first sentence.} This is the second sentence.

jshell> import java.io.*

jshell> var a = new StringReader("hello world")
a ==> java.io.StringReader@3abbfa04

jshell> var b = new StringWriter()
b ==>

jshell> a.transferTo(b)
$4 ==> 11

jshell> b
b ==> hello world

jshell> import java.lang.management.*

jshell> ProcessHandle.current()
$1 ==> 20674 (1)

jshell> ManagementFactory.getRuntimeMXBean().getPid()
$2 ==> 11429 (2)

Set<Integer> set = Set.of(1,2,3,4);
List<Integer> list = List.of(1,2,1,2);
Map<String, Integer> map = Map.of("key1", 1, "key2", 2);
Map<String, Integer> mapLonger = Map.ofEntries(Map.entry("key1", 1), Map.entry("key2", 2));

jshell> List<Object> list = new ArrayList<>()
list ==> []

jshell> List<Object> unmodifiableList = Collections.unmodifiableList(list)
unmodifiableList ==> []

jshell> list.add(1) (1)
$3 ==> true

jshell> unmodifiableList (1)
unmodifiableList ==> [1]

jshell> List<Object> immutableList = List.of();
immutableList ==> []

jshell> immutableList.add(1)
|  Exception java.lang.UnsupportedOperationException
|        at ImmutableCollections.uoe (ImmutableCollections.java:71)
|        at ImmutableCollections$AbstractImmutableCollection.add (ImmutableCollections.java:75)
|        at (#6:1)

jshell> List<Integer> a = List.of(1,2,3)
a ==> [1, 2, 3]

jshell> List<Integer> b = List.copyOf(a)
b ==> [1, 2, 3]

jshell> a == b
$7 ==> true

jshell> Set.of(1,1)
|  java.lang.IllegalArgumentException thrown: duplicate element: 1
|        at ImmutableCollections$SetN.<init> (ImmutableCollections.java:463)
|        at Set.of (Set.java:521)

jshell> List<Optional<Integer>> data = List.of(Optional.of(42), Optional.empty(), Optional.of(-1));
data ==> [Optional[42], Optional.empty, Optional[-1]]

jshell> data.stream().filter(Optional::isPresent).map(Optional::get).collect(Collectors.toList()); (1)
$1 ==> [42, -1]

jshell> data.stream().flatMap(Optional::stream).collect(Collectors.toList()); (2)
$2 ==> [42, -1]
List<Optional<String>> listOfOptionals = something();

public Stream<T> stream() {
    if (!isPresent()) {
        return Stream.empty();
    } else {
        return Stream.of(value);
    }
}

IntStream
  .iterate(1, n -> n + 1)
  .takeWhile(n -> n < 10)
  .forEach(System.out::println);

import java.lang.StackWalker.Option;
import java.util.logging.Logger;

public class LoggerFactory {
        public static Logger forEnclosingClass() {
                Class<?> callerClass = StackWalker.getInstance(Option.RETAIN_CLASS_REFERENCE).getCallerClass();
                return Logger.getLogger(callerClass.getCanonicalName());
        }
}

// client code
public class Demo {

    private final Logger logger = LoggerFactory.forEnclosingClass();

}

jshell> Predicate<Integer> pred = _ -> false;
|  Error:
|  '_' used as an identifier
|    (use of '_' as an identifier is forbidden for lambda parameters)
|  Predicate<Integer> pred = _ -> false;
|                            ^

String version = Runtime.class.getPackage().getImplementationVersion();

double version = Double.parseDouble(System.getProperty("java.specification.version"));

String[] javaVersionElements = System.getProperty("java.runtime.version").split("\\.|_|-b");

Runtime.Version version = Runtime.version();

import java.lang.Runtime.Version;
import java.lang.System;

String versionString = System.getProperty("java.version");
Version version = Version.parse(versionString);
System.out.printf("java %d.%d%n", version.major(), version.minor());

ProcessHandle self = ProcessHandle.current();
ProcessHandle.Info procInfo = self.info();
System.out.println(procInfo);

ProcessHandle.allProcesses().map(ProcessHandle::info).forEach(System.out::println);

[user: Optional[dfa], cmd: /Library/Java/JavaVirtualMachines/jdk-11.jdk/Contents/Home/bin/java, args: [-agentlib:jdwp=transport=dt_socket,address=localhost:61581, jdk.jshell.execution.RemoteExecutionControl, 61580], startTime: Optional[2018-10-19T06:15:44.622Z], totalTime: Optional[PT0.459124S]]
[user: Optional[dfa], cmd: /Library/Java/Home//bin/jshell, startTime: Optional[2018-10-19T06:15:44.225Z]]
[user: Optional[root], startTime: Optional[2018-10-19T06:14:33.378Z]]
[user: Optional[dfa], cmd: /System/Library/PrivateFrameworks/AOSKit.framework/Versions/A/XPCServices/com.apple.iCloudHelper.xpc/Contents/MacOS/com.apple.iCloudHelper, startTime: Optional[2018-10-19T06:14:33.081Z]]
[user: Optional[dfa], cmd: /Library/Java/JavaVirtualMachines/jdk-11.jdk/Contents/Home/bin/java, args: [-agentlib:jdwp=transport=dt_socket,address=localhost:61572, jdk.jshell.execution.RemoteExecutionControl, 61571], startTime: Optional[2018-10-19T06:14:32.070Z]]
...

@Deprecate(forRemoval=true)
public void foo() {

}

@Deprecate(since="1.0")
public void bar() {

}

$ java -Xlog:gc* -jar myapp.jar
[0.012s][info][gc,heap] Heap region size: 1M
[0.018s][info][gc     ] Using G1
[0.019s][info][gc,heap,coops] Heap address: 0x00000006c0000000, size: 4096 MB, Compressed Oops mode: Zero based, Oop shift amount: 3
... application output
... exit
[1.803s][info][gc,heap,exit ] Heap
[1.803s][info][gc,heap,exit ]  garbage-first heap   total 262144K, used 11264K [0x00000006c0000000, 0x00000007c0000000)
[1.803s][info][gc,heap,exit ]   region size 1024K, 12 young (12288K), 0 survivors (0K)
[1.803s][info][gc,heap,exit ]  Metaspace       used 10805K, capacity 11186K, committed 11520K, reserved 1058816K
[1.803s][info][gc,heap,exit ]   class space    used 1042K, capacity 1203K, committed 1280K, reserved 1048576K

$ java -Xlog:gc,gc+heap -jar myapp.jar
[0.013s][info][gc,heap] Heap region size: 1M
[0.019s][info][gc     ] Using G1
... application output
[89.471s][info][gc,heap] GC(0) Eden regions: 24->0(151)
[89.471s][info][gc,heap] GC(0) Survivor regions: 0->2(3)
[89.471s][info][gc,heap] GC(0) Old regions: 0->0
[89.471s][info][gc,heap] GC(0) Humongous regions: 0->0
[89.471s][info][gc     ] GC(0) Pause Young (G1 Evacuation Pause) 24M->1M(256M) 3.926ms
... exit

public static SecureRandom getInstanceStrong()
                                      throws NoSuchAlgorithmException

jshell> Integer.MAX_VALUE * 2 (1)
$1 ==> -2
jshell> Math.multiplyExact(Integer.MAX_VALUE, 2) (2)
|  Exception java.lang.ArithmeticException: integer overflow
|        at Math.multiplyExact (Math.java:906)
|        at (#2:1)

jshell> String.join(",");
$10 ==> ""

jshell> String.join(",", "a");
$11 ==> "a"

jshell> String.join(",", "a", "b");
$12 ==> "a,b"

jshell> void foo(List<String> args) { System.out.println(args); }
|  created method foo(List<String>)

jshell> foo(Collections.<String>emptyList()) (1)
[]

jshell> foo(Collections.emptyList()) (2)
[a, b]

jshell> public class Foo {
   ...>   public void foo() { }
   ...> }
|  created class Foo (1)

jshell> public class Foo2 {
   ...>   public void foo(Foo2 this) { }
   ...> }
|  created class Foo2 (2)

jshell> int[] array = new int[10]
array ==> int[10] { 0, 0, 0, 0, 0, 0, 0, 0, 0, 0 }

jshell> Arrays.setAll(array, idx -> idx + 1)

jshell> array
array ==> int[10] { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 }

jshell> Arrays.parallelPrefix(array, (acc, e) -> acc + e)

jshell> array
array ==> int[10] { 1, 3, 6, 10, 15, 21, 28, 36, 45, 55 }

jshell> int[] triangularNumber(int n) {
   ...>   int[] result = new int[n];
   ...>   Arrays.parallelSetAll(result, idx -> idx + 1);
   ...>   Arrays.parallelPrefix(result, (acc, e) -> acc + e);
   ...>   return result;
   ...> }
|  created method triangularNumber(int)

jshell> triangularNumber(4)
$1 ==> int[4] { 1, 3, 6, 10 }

jshell> triangularNumber(10)
$2 ==> int[10] { 1, 3, 6, 10, 15, 21, 28, 36, 45, 55 }

jshell> triangularNumber(100)
$3 ==> int[100] { 1, 3, 6, 10, 15, 21, 28, 36, 45, 55, 66, 78, 91, 105, 120, 136, 153, 171, 190, 210, 231, 253, 276, 300, 325, 351, 378, 406, 435, 465, 496, 528, 561, 595, 630, 666, 703, 741, 780, 820, 861, 903, 946, 990, 1035, 1081, 1128, 1176, 1225, 1275, 1326, 1378, 1431, 1485, 1540, 1596, 1653, 1711, 1770, 1830, 1891, 1953, 2016, 2080, 2145, 2211, 2278, 2346, 2415, 2485, 2556, 2628, 2701, 2775, 2850, 2926, 3003, 3081, 3160, 3240, 3321, 3403, 3486, 3570, 3655, 3741, 3828, 3916, 4005, 4095, 4186, 4278, 4371, 4465, 4560, 4656, 4753, 4851, 4950, 5050 }