Adjust tests for Java 21 & add helper for performance testing

Common/src/main/java/pl/mperor/lab/common/TestUtils.java

@@ -60,4 +60,11 @@ private E getNext(int index) {
         }
     }
 
+    public static long measureExecutionTimeMillis(Runnable task) {
+        long startTime = System.currentTimeMillis();
+        task.run();
+        long endTime = System.currentTimeMillis();
+        return endTime - startTime;
+    }
+
 }

JavaReleases/src/test/java/pl/mperor/lab/java/Java21.java

@@ -4,10 +4,11 @@
 import org.junit.jupiter.api.Test;
 import pl.mperor.lab.common.TestUtils;
 
-import java.util.Collections;
-import java.util.List;
-import java.util.NoSuchElementException;
-import java.util.SequencedCollection;
+import java.time.Duration;
+import java.util.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.stream.IntStream;
 
 /// Java 21™ (September 2023)
 /// [JDK 21](https://openjdk.org/projects/jdk/21)
@@ -35,6 +36,7 @@ public class Java21 {
     @Test
     public void testVirtualThreads() throws InterruptedException {
         TestUtils.ReadableOut out = TestUtils.setTempSystemOut();
+        // same as Thread.ofVirtual().start(() -> ...)
         Thread virtualThread = Thread.startVirtualThread(() ->
                 System.out.print("Hello from Virtual Thread!")
         );
@@ -46,13 +48,45 @@ public void testVirtualThreads() throws InterruptedException {
         Assertions.assertEquals("Hello from Virtual Thread!", out.all());
     }
 
+
+    @Test
+    public void testVirtualVsPlatformThreads() {
+        final int threadPool = 100;
+
+        long virtualThreadsTime = TestUtils.measureExecutionTimeMillis(() -> {
+                    try (var executor = Executors.newVirtualThreadPerTaskExecutor()) {
+                        execute(threadPool, executor);
+                    }
+                }
+        );
+
+        long platformThreadsTime = TestUtils.measureExecutionTimeMillis(() -> {
+                    try (var executor = Executors.newFixedThreadPool(threadPool)) {
+                        execute(threadPool, executor);
+                    }
+                }
+        );
+
+        System.out.println("🌀 virtual threads: %s [ms]".formatted(virtualThreadsTime));
+        System.out.println("🖥️ platform threads: %s [ms]".formatted(platformThreadsTime));
+        Assertions.assertTrue(platformThreadsTime > virtualThreadsTime);
+    }
+
+    private static void execute(int threadPool, ExecutorService executor) {
+        IntStream.rangeClosed(0, threadPool).forEach(i -> executor.submit(() -> {
+            Thread.sleep(Duration.ofMillis(100));
+            return i;
+        }));
+    }
+
     @Test
     public void testSequencedCollections() {
         List<String> letters = List.of("one", "two", "three");
-        Assertions.assertInstanceOf(SequencedCollection.class, letters);
         Assertions.assertEquals("one", letters.getFirst());
         Assertions.assertEquals("three", letters.getLast());
         Assertions.assertThrows(NoSuchElementException.class, Collections.emptyList()::getFirst);
+        Assertions.assertInstanceOf(SequencedCollection.class, letters);
+        Assertions.assertInstanceOf(SequencedCollection.class, new LinkedHashMap<>().keySet());
     }
 
     @Test
@@ -70,7 +104,8 @@ record LineSegment(Point start, Point end) {}
 
     @Test
     public void testSwitchPatternMatching() {
-        Assertions.assertEquals("String: Hello", switchOverClasses("Hello"));
+        Assertions.assertEquals("Short String: abc", switchOverClasses("abc"));
+        Assertions.assertEquals("Long String: longer than abc", switchOverClasses("longer than abc"));
         Assertions.assertEquals("int: 1", switchOverClasses(1));
         Assertions.assertEquals("long: 13", switchOverClasses(13L));
         Assertions.assertEquals("boolean: true", switchOverClasses(true));
@@ -86,7 +121,8 @@ public String toString() {
 
     private static String switchOverClasses(Object obj) {
         return switch (obj) {
-            case String s -> String.format("String: %s", s);
+            case String s when s.length() <= 3 -> String.format("Short String: %s", s);
+            case String s -> String.format("Long String: %s", s);
             case Integer i -> String.format("int: %d", i);
             case Long l -> String.format("long: %d", l);
             case Boolean b -> String.format("boolean: %s", b);