Update test class for Java 15 ...

- samples only for standard features
- markdown javadoc for JEPs
- organize classes related to Java 15
- improve code readability

Author: mperor

src/main/java/pl/mperor/lab/java/Hidden.java

@@ -0,0 +1,7 @@
+package pl.mperor.lab.java;
+
+public interface Hidden {
+    static int lookup() {
+        return 1;
+    }
+}

src/test/java/pl/mperor/lab/java/Java13.java

@@ -9,23 +9,4 @@
  * Java 13 (September 2019)
  */
 public class Java13 {
-
-    @Test
-    public void testTextBlock() {
-        String json = """
-                {
-                    "login": "admin",
-                    "password": "*****"
-                }
-                """;
-
-        Assertions.assertTrue(json.contains("\"login\": \"admin\""));
-    }
-
-    @Test
-    public void testStringFormatted() {
-        Assertions.assertEquals("Hello World!", "Hello %s".formatted("World!"));
-        Assertions.assertEquals("Value: 0.00", String.format(Locale.US, "Value: %.2f", 0d));
-    }
-
 }

src/test/java/pl/mperor/lab/java/Java15.java

@@ -1,8 +1,99 @@
 package pl.mperor.lab.java;
 
-/**
- * Java 15 (September 2020)
- */
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.invoke.MethodType;
+import java.net.DatagramSocket;
+import java.net.SocketException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.security.*;
+import java.util.Locale;
+
+/// Java 15™ (September 2020)
+/// [JDK 15](https://openjdk.org/projects/jdk/15)
+///
+/// - STANDARD FEATURES:
+///     - 378:	Text Blocks
+///     - 339:	Edwards-Curve Digital Signature Algorithm (EdDSA)
+///     - 371:	Hidden Classes
+///     - 372:	Remove the Nashorn JavaScript Engine
+///     - 373:	Reimplement the Legacy DatagramSocket API
+///     - 374:	Disable and Deprecate Biased Locking
+///     - 377:	ZGC: A Scalable Low-Latency Garbage Collector
+///     - 379:	Shenandoah: A Low-Pause-Time Garbage Collector
+///     - 381:	Remove the Solaris and SPARC Ports
+///     - 385:	Deprecate RMI Activation for Removal [Java17#testRmiActivationRemoved()]
+///
+/// - PREVIEW & INCUBATOR:
+///     - 360:	Sealed Classes (Preview)
+///     - 375:	Pattern Matching for instanceof (Second Preview)
+///     - 384:	Records (Second Preview)
+///     - 383:	Foreign-Memory Access API (Second Incubator)
 public class Java15 {
 
+    @Test
+    public void testTextBlock() {
+        String json = """
+                {
+                    "login": "admin",
+                    "password": "*****"
+                }
+                """;
+
+        Assertions.assertTrue(json.contains("\"login\": \"admin\""));
+    }
+
+    @Test
+    public void testStringFormatted() {
+        Assertions.assertEquals("Hello World!", "Hello %s".formatted("World!"));
+        Assertions.assertEquals("Value: 0.00", String.format(Locale.US, "Value: %.2f", 0d));
+    }
+
+    @Test
+    public void testEdwardsCurveDigitalSignatureAlgorithm() throws NoSuchAlgorithmException, InvalidKeyException, SignatureException {
+        String edwardsAlgorithm = "Ed25519";
+        KeyPairGenerator generator = KeyPairGenerator.getInstance(edwardsAlgorithm);
+        KeyPair keyPair = generator.generateKeyPair();
+        byte[] bytes = "secret".getBytes();
+
+        Signature sig = Signature.getInstance(edwardsAlgorithm);
+        sig.initSign(keyPair.getPrivate());
+        sig.update(bytes);
+        byte[] signed = sig.sign();
+
+        Signature verificationSignature = Signature.getInstance(edwardsAlgorithm);
+        verificationSignature.initVerify(keyPair.getPublic());
+        verificationSignature.update(bytes);
+        Assertions.assertTrue(verificationSignature.verify(signed));
+    }
+
+    @Test
+    public void testHiddenClass() throws Throwable {
+        Path path = Paths.get("build/classes/java/main/pl/mperor/lab/java/Hidden.class");
+
+        MethodHandles.Lookup lookup = MethodHandles.lookup();
+        Class<?> hiddenClass = lookup.defineHiddenClass(Files.readAllBytes(path), true, MethodHandles.Lookup.ClassOption.NESTMATE)
+                .lookupClass();
+        MethodHandle methodHandle = lookup.findStatic(hiddenClass, "lookup", MethodType.methodType(int.class));
+        Assertions.assertEquals(1, methodHandle.invoke());
+    }
+
+    @Test
+    public void testNashornEngineRemoved() {
+        Assertions.assertThrows(ClassNotFoundException.class, () -> {
+            Class.forName("jdk.nashorn.api.scripting.NashornScriptEngineFactory");
+        });
+    }
+
+    @Test
+    public void testDatagramSocket() throws SocketException {
+        DatagramSocket datagramSocket = new DatagramSocket();
+        Assertions.assertNotNull(datagramSocket);
+    }
+
 }

src/test/java/pl/mperor/lab/java/Java16.java

@@ -29,9 +29,9 @@
 ///     - 394:	Pattern Matching for instanceof
 ///     - 390:	Warnings for Value-Based Classes
 ///     - 392:	Packaging Tool
-///     - 396:	Strongly Encapsulate JDK Internals by Default
-///     - 376:	ZGC: Concurrent Thread-Stack Processing
 ///     - 380:	Unix-Domain Socket Channels
+///     - 396:	Strongly Encapsulate JDK Internals by Default [Java17#testStronglyEncapsulatedInternals()]
+///     - 376:	ZGC: Concurrent Thread-Stack Processing
 ///     - 387:	Elastic Metaspace
 ///     - 347:	Enable C++14 Language Features
 ///     - 386:	Alpine Linux Port

src/test/java/pl/mperor/lab/java/Java17.java

@@ -78,9 +78,14 @@ public String call() {
         }
     }
 
+    /**
+     * You may need this JVM argument:
+     * --add-opens java.base/java.lang=ALL-UNNAMED
+     */
     @Test
     public void testStronglyEncapsulatedInternals() {
         Assertions.assertThrows(InaccessibleObjectException.class, () -> deepLookIntoStringBytes("Hello"));
+        new ProcessBuilder("java", "--add-opens", "java.base/java.lang=ALL-UNNAMED");
     }
 
     private static byte[] deepLookIntoStringBytes(String string) throws IllegalAccessException, NoSuchFieldException {
@@ -132,7 +137,7 @@ public void testDeprecated() {
     }
 
     @Test
-    public void testRmiActivation() {
+    public void testRmiActivationRemoved() {
         Assertions.assertFalse(ModuleLayer.boot().findModule("java.rmi").stream()
                 .map(Module::getPackages)
                 .flatMap(Set::stream)