Update test classes for Java 4, 5, 12, and 15

- add new test cases for Collections API, formatted string handling, JavaBeans EventHandler, and NIO features
- improve code documentation and readability

Author: mperor

JavaReleases/src/test/java/pl/mperor/lab/java/Java12.java

@@ -62,7 +62,7 @@ private String generateFileHashMD5(Path file) throws NoSuchAlgorithmException, I
 
         StringBuilder sb = new StringBuilder();
         for (byte b : hashBytes) {
-            sb.append(String.format("%02x", b));
+            sb.append(String.format("%02x", b)); // byte to 2‑digit hex
         }
         return sb.toString();
     }

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

@@ -62,7 +62,15 @@ public void testTextBlock() {
 
     @Test
     public void testStringFormatted() {
-        Assertions.assertEquals("Hello World!", "Hello %s".formatted("World!"));
+        var positionInFormatted = """
+                user: %1$s
+                last name: %2$s
+                name: %1$s""".formatted("John", "Smith");
+        Assertions.assertEquals("""
+                user: John
+                last name: Smith
+                name: John""", positionInFormatted);
+
         Assertions.assertEquals("Value: 0.00", String.format(Locale.US, "Value: %.2f", 0d));
     }
 

JavaReleases/src/test/java/pl/mperor/lab/java/Java4.java

@@ -2,16 +2,21 @@
 
 import org.junit.jupiter.api.Assertions;
 import org.junit.jupiter.api.Test;
+import pl.mperor.lab.common.TestUtils;
 
 import javax.imageio.ImageIO;
 import java.awt.image.BufferedImage;
+import java.beans.EventHandler;
 import java.io.*;
 import java.net.InetSocketAddress;
 import java.net.ServerSocket;
 import java.nio.channels.ServerSocketChannel;
 import java.nio.channels.SocketChannel;
 import java.nio.file.Files;
 import java.nio.file.Path;
+import java.nio.file.attribute.BasicFileAttributes;
+import java.nio.file.attribute.FileTime;
+import java.time.Instant;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.Executors;
 import java.util.logging.Logger;
@@ -37,8 +42,12 @@ public void testNewInputOutputAkaNIO() throws IOException {
         Path path = Path.of("src", "test", "resources", "nio.txt");
         byte[] fileBytes = Files.readAllBytes(path);
         String content = new String(fileBytes);
-
         Assertions.assertEquals("Hello NIO!", content);
+
+        var fileCreationTime = Files.readAttributes(path, BasicFileAttributes.class)
+                .creationTime();
+        System.out.printf("📃 File '%s' - last access time: ⌚%s%n: ", path.getFileName(), fileCreationTime);
+        Assertions.assertTrue(fileCreationTime.compareTo(FileTime.from(Instant.now())) <= 0);
     }
 
     @Test
@@ -125,4 +134,17 @@ private void handleConnectedClient(ServerSocket serverSocket) throws IOException
         }
     }
 
+    @Test
+    public void testJavaBeansEventHandler() {
+        var out = TestUtils.setTempSystemOut();
+        Runnable runnable = EventHandler.create(Runnable.class, this, "run"); // () -> run();
+        runnable.run();
+        Assertions.assertEquals("Run was called!", out.all());
+        TestUtils.resetSystemOut();
+    }
+
+    public void run() {
+        System.out.print("Run was called!");
+    }
+
 }

JavaReleases/src/test/java/pl/mperor/lab/java/Java5.java

@@ -8,6 +8,7 @@
 import java.lang.annotation.*;
 import java.lang.reflect.Method;
 import java.util.Arrays;
+import java.util.Collections;
 import java.util.List;
 import java.util.concurrent.*;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -146,4 +147,14 @@ public void testStringBuilderInsteadOfStringBuffer() {
         Assertions.assertEquals("Hello World", sb.reverse().toString());
     }
 
+    @Test
+    public void testCollectionsAPI() {
+        var collection = List.of(1,2,3,2,2);
+        Assertions.assertEquals(3, Collections.frequency(collection, 2));
+
+        List<String> empty = Collections.emptyList();
+        Assertions.assertNotNull(empty);
+        Assertions.assertTrue(empty.isEmpty());
+    }
+
 }