Add java11-features module: runnable demos and captured output for the ankurm.com java11-features article

README.md

@@ -101,3 +101,4 @@ MIT licensed, see `LICENSE`.
 
 Modules for the Java 8 / 11 / 17 / 21 feature articles, one folder each, each with `src/`, `broken/`, `output/` and `run.sh`:
 - `java8-features/` — see its README
+- `java11-features/` — see its README

java11-features/README.md

@@ -0,0 +1,13 @@
+# java11-features — Java 11 features with examples
+
+Companion code for the ankurm.com article **Java 11 Features with Examples (and What Changed from Java 8)**. The explanation lives in the article; this folder holds the runnable sources and the transcripts they produced. There is no `docs/` folder: the depth is inside the article itself.
+
+```bash
+JDK8=/path/to/jdk8 JDK11=/path/to/jdk11 ./run.sh      # regenerates output/*.txt
+```
+
+- `src/` compiles and runs unchanged on the JDK named in each output header.
+- `broken/` fails to compile on purpose; the compiler's own message is committed in `output/`.
+- `output/` is real captured output, regenerated by `run.sh`.
+
+Tested on: Temurin 1.8.0_504 and 11.0.32.1.

java11-features/broken/JaxbRemoved.java

@@ -0,0 +1,8 @@
+import javax.xml.bind.JAXBContext;
+
+/** Compiles on 8, fails on 11: JEP 320 removed the Java EE modules (java.xml.bind and friends). */
+public class JaxbRemoved {
+    public static void main(String[] args) throws Exception {
+        System.out.println(JAXBContext.class.getName());
+    }
+}

java11-features/broken/VarWithoutLambda.java

@@ -0,0 +1,9 @@
+import java.util.function.BiFunction;
+
+/** Fails to compile on purpose: you cannot mix var and explicit types in one lambda's parameters. */
+public class VarWithoutLambda {
+    public static void main(String[] args) {
+        BiFunction<Integer, Integer, Integer> f = (var a, Integer b) -> a + b;
+        System.out.println(f.apply(1, 2));
+    }
+}

java11-features/output/01-string-methods.txt

@@ -0,0 +1,7 @@
+$ javac src/StringMethods.java && java StringMethods     (11.0.32.1)
+trim() length   : 9
+strip() length  : 5
+isBlank("  ")   : true   isEmpty: false
+lines()         : [a, b, c]
+repeat(3)       : ababab
+stripLeading    : [x ]  stripTrailing: [  x]

java11-features/output/02-files.txt

@@ -0,0 +1,3 @@
+$ javac src/FilesDemo.java && java FilesDemo     (11.0.32.1)
+read back       : one|two|three
+Path.of         : a/b/c.txt

java11-features/output/03-http-client.txt

@@ -0,0 +1,4 @@
+$ javac src/HttpClientDemo.java && java HttpClientDemo     (11.0.32.1)
+sync            : 200 hello from server version=HTTP_1_1
+header          : X-Demo=yes
+async           : hello from server

java11-features/output/04-var-lambda.txt

@@ -0,0 +1,3 @@
+$ javac src/VarLambda.java && java VarLambda     (11.0.32.1)
+(var a, var b)  : 5
+with annotation : x-y

java11-features/output/05-single-file.txt

@@ -0,0 +1,2 @@
+$ java src/SingleFile.java     (11.0.32.1)
+launched from source, java.version=11.0.32.1

java11-features/output/06-nest-mates.txt

@@ -0,0 +1,4 @@
+$ javac src/NestMates.java && java NestMates     (11.0.32.1)
+nest host       : NestMates
+inner can read  : 42
+access$ methods on outer: 0

java11-features/output/07-compile-errors.txt

@@ -0,0 +1,20 @@
+$ javac broken/JaxbRemoved.java     (1.8.0_504)
+(compiled cleanly)
+
+$ javac broken/JaxbRemoved.java     (11.0.32.1)
+broken/JaxbRemoved.java:1: error: package javax.xml.bind does not exist
+import javax.xml.bind.JAXBContext;
+                     ^
+broken/JaxbRemoved.java:6: error: cannot find symbol
+        System.out.println(JAXBContext.class.getName());
+                           ^
+  symbol:   class JAXBContext
+  location: class JaxbRemoved
+2 errors
+
+$ javac broken/VarWithoutLambda.java     (11.0.32.1)
+broken/VarWithoutLambda.java:6: error: invalid lambda parameter declaration
+        BiFunction<Integer, Integer, Integer> f = (var a, Integer b) -> a + b;
+                                                  ^
+  (cannot mix 'var' and explicitly-typed parameters)
+1 error

java11-features/output/08-string-methods-on-8.txt

@@ -0,0 +1,33 @@
+# trim vs strip on the same string, Java 8 has no strip(); the Java 8 compile of src/StringMethods.java:
+$ javac src/StringMethods.java     (1.8.0_504)
+src/StringMethods.java:9: error: cannot find symbol
+        System.out.println("strip() length  : " + padded.strip().length());
+                                                        ^
+  symbol:   method strip()
+  location: variable padded of type String
+src/StringMethods.java:10: error: cannot find symbol
+        System.out.println("isBlank(\"  \")   : " + "  ".isBlank() + "   isEmpty: " + "  ".isEmpty());
+                                                        ^
+  symbol:   method isBlank()
+  location: class String
+src/StringMethods.java:11: error: cannot find symbol
+        System.out.println("lines()         : " + "a\nb\r\nc".lines().collect(Collectors.toList()));
+                                                             ^
+  symbol:   method lines()
+  location: class String
+src/StringMethods.java:12: error: cannot find symbol
+        System.out.println("repeat(3)       : " + "ab".repeat(3));
+                                                      ^
+  symbol:   method repeat(int)
+  location: class String
+src/StringMethods.java:13: error: cannot find symbol
+        System.out.println("stripLeading    : [" + "  x ".stripLeading() + "]  stripTrailing: [" + "  x ".stripTrailing() + "]");
+                                                         ^
+  symbol:   method stripLeading()
+  location: class String
+src/StringMethods.java:13: error: cannot find symbol
+        System.out.println("stripLeading    : [" + "  x ".stripLeading() + "]  stripTrailing: [" + "  x ".stripTrailing() + "]");
+                                                                                                         ^
+  symbol:   method stripTrailing()
+  location: class String
+6 errors

java11-features/run.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+# Java 11 features: every demo compiled and run on real JDKs; regenerates output/*.txt
+#   JDK8=/path JDK11=/path ./run.sh
+set -uo pipefail
+unset JAVA_TOOL_OPTIONS
+HERE="$(cd "$(dirname "$0")" && pwd)"
+JDK8="${JDK8:-/opt/jdks/jdk8}"; JDK11="${JDK11:-/opt/jdks/jdk11}"
+OUT="$HERE/output"; mkdir -p "$OUT"; B="$(mktemp -d)"; trap 'rm -rf "$B"' EXIT
+cd "$HERE"
+ver() { "$1/bin/java" -version 2>&1 | sed -n 1p | sed 's/.*"\(.*\)".*/\1/'; }
+cr() { local jdk="$1" src="$2" cls="$3" o; o="$(mktemp -d -p "$B")"
+  echo "\$ javac $src && java $cls     ($(ver "$jdk"))"
+  "$jdk/bin/javac" -encoding UTF-8 -d "$o" "$src" 2>&1 | grep -v '^Note:'; "$jdk/bin/java" -cp "$o" "$cls" 2>&1; }
+co() { local jdk="$1" src="$2" o; o="$(mktemp -d -p "$B")"
+  echo "\$ javac $src     ($(ver "$jdk"))"; local r; r="$("$jdk/bin/javac" -encoding UTF-8 -d "$o" "$src" 2>&1)"; if [ -n "$r" ]; then echo "$r"; else echo "(compiled cleanly)"; fi; }
+cr "$JDK11" src/StringMethods.java StringMethods   > "$OUT/01-string-methods.txt"
+cr "$JDK11" src/FilesDemo.java FilesDemo           > "$OUT/02-files.txt"
+cr "$JDK11" src/HttpClientDemo.java HttpClientDemo > "$OUT/03-http-client.txt"
+cr "$JDK11" src/VarLambda.java VarLambda           > "$OUT/04-var-lambda.txt"
+{ echo "\$ java src/SingleFile.java     ($(ver "$JDK11"))"; "$JDK11/bin/java" src/SingleFile.java 2>&1; } > "$OUT/05-single-file.txt"
+cr "$JDK11" src/NestMates.java NestMates           > "$OUT/06-nest-mates.txt"
+{ co "$JDK8" broken/JaxbRemoved.java; echo; co "$JDK11" broken/JaxbRemoved.java; echo; co "$JDK11" broken/VarWithoutLambda.java; } > "$OUT/07-compile-errors.txt"
+{ echo "# the Java 8 compile of src/StringMethods.java: these String methods do not exist on 8"; co "$JDK8" src/StringMethods.java; } > "$OUT/08-string-methods-on-8.txt"
+exit 0

java11-features/src/FilesDemo.java

@@ -0,0 +1,13 @@
+import java.nio.file.*;
+
+/** Files.readString / writeString and Path.of, new in 11. */
+public class FilesDemo {
+    public static void main(String[] args) throws Exception {
+        Path p = Files.createTempFile("demo", ".txt");
+        Files.writeString(p, "one\ntwo\nthree");
+        String s = Files.readString(p);
+        System.out.println("read back       : " + s.replace("\n", "|"));
+        System.out.println("Path.of         : " + Path.of("a", "b", "c.txt"));
+        Files.delete(p);
+    }
+}

java11-features/src/HttpClientDemo.java

@@ -0,0 +1,30 @@
+import com.sun.net.httpserver.HttpServer;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.http.*;
+import java.util.concurrent.CompletableFuture;
+
+/** The standard java.net.http client (JEP 321): sync, async, against a local server so the output is stable. */
+public class HttpClientDemo {
+    public static void main(String[] args) throws Exception {
+        HttpServer server = HttpServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
+        server.createContext("/hello", ex -> {
+            byte[] body = "hello from server".getBytes();
+            ex.getResponseHeaders().add("X-Demo", "yes");
+            ex.sendResponseHeaders(200, body.length);
+            ex.getResponseBody().write(body); ex.close();
+        });
+        server.start();
+        String url = "http://127.0.0.1:" + server.getAddress().getPort() + "/hello";
+        HttpClient client = HttpClient.newHttpClient();
+        HttpRequest req = HttpRequest.newBuilder(URI.create(url)).GET().build();
+
+        HttpResponse<String> r = client.send(req, HttpResponse.BodyHandlers.ofString());
+        System.out.println("sync            : " + r.statusCode() + " " + r.body() + " version=" + r.version());
+        System.out.println("header          : X-Demo=" + r.headers().firstValue("X-Demo").orElse("?"));
+
+        CompletableFuture<String> f = client.sendAsync(req, HttpResponse.BodyHandlers.ofString()).thenApply(HttpResponse::body);
+        System.out.println("async           : " + f.get());
+        server.stop(0);
+    }
+}

java11-features/src/NestMates.java

@@ -0,0 +1,13 @@
+import java.lang.reflect.Modifier;
+
+/** JEP 181: nest-based access. Private members of nest mates no longer need synthetic accessor methods. */
+public class NestMates {
+    private int secret = 42;
+    static class Inner { int peek(NestMates n) { return n.secret; } }
+    public static void main(String[] args) {
+        System.out.println("nest host       : " + Inner.class.getNestHost().getSimpleName());
+        System.out.println("inner can read  : " + new Inner().peek(new NestMates()));
+        long synthetic = java.util.Arrays.stream(NestMates.class.getDeclaredMethods()).filter(m -> m.getName().startsWith("access$")).count();
+        System.out.println("access$ methods on outer: " + synthetic);
+    }
+}

java11-features/src/SingleFile.java

@@ -0,0 +1,6 @@
+/** Run directly with:  java SingleFile.java   (JEP 330, no javac step). */
+public class SingleFile {
+    public static void main(String[] args) {
+        System.out.println("launched from source, java.version=" + System.getProperty("java.version"));
+    }
+}

java11-features/src/StringMethods.java

@@ -0,0 +1,15 @@
+import java.util.stream.Collectors;
+
+/** The String additions in Java 11: isBlank, lines, strip, repeat. */
+public class StringMethods {
+    public static void main(String[] args) {
+        String em = String.valueOf((char) 0x2003);          // EM SPACE: whitespace to strip(), not to trim()
+        String padded = em + " hello " + em;
+        System.out.println("trim() length   : " + padded.trim().length());
+        System.out.println("strip() length  : " + padded.strip().length());
+        System.out.println("isBlank(\"  \")   : " + "  ".isBlank() + "   isEmpty: " + "  ".isEmpty());
+        System.out.println("lines()         : " + "a\nb\r\nc".lines().collect(Collectors.toList()));
+        System.out.println("repeat(3)       : " + "ab".repeat(3));
+        System.out.println("stripLeading    : [" + "  x ".stripLeading() + "]  stripTrailing: [" + "  x ".stripTrailing() + "]");
+    }
+}

java11-features/src/VarLambda.java

@@ -0,0 +1,15 @@
+import java.util.function.BiFunction;
+
+/** JEP 323: var in lambda parameters. The point is annotations, not brevity. */
+public class VarLambda {
+    @java.lang.annotation.Retention(java.lang.annotation.RetentionPolicy.RUNTIME)
+    @java.lang.annotation.Target(java.lang.annotation.ElementType.PARAMETER)
+    @interface NonNull {}
+
+    public static void main(String[] args) {
+        BiFunction<Integer, Integer, Integer> add = (var a, var b) -> a + b;
+        BiFunction<String, String, String> join = (@NonNull var a, @NonNull var b) -> a + "-" + b;
+        System.out.println("(var a, var b)  : " + add.apply(2, 3));
+        System.out.println("with annotation : " + join.apply("x", "y"));
+    }
+}