Java 14 examples

Author: wesleyegberto

.gitignore

@@ -13,4 +13,6 @@ output/
 hs_err_pid*
 .vscode/
 .DS_Store
-*.data
+*.data
+jdt.ls-java-project/
+*.dmg

java-14/HelpfulNPEMessages.java

@@ -0,0 +1,63 @@
+import static java.util.stream.Collectors.toList;
+
+import java.util.stream.IntStream;
+
+/**
+ * To run: `java -XX:+ShowCodeDetailsInExceptionMessages HelpfulNPEMessages.java`
+ */
+public class HelpfulNPEMessages {
+	public static void main(String[] args) {
+		simpleObjectAccess();
+		insideStreams();
+	}
+
+	private static void simpleObjectAccess() {
+		System.out.println("=== Simple Object Attribute Access ===");
+		try {
+			var thing = new Thing(11);
+			System.out.println("Value " + thing.weight.value);
+		} catch (NullPointerException ex) {
+			ex.printStackTrace();
+		}
+	}
+
+	private static void insideStreams() {
+		System.out.println("%n=== Attribute Access Inside Streams ===");
+		try {
+			IntStream.of(2, 4, 6, 8, 9)
+				.mapToObj(Thing::new)
+				.map(thing -> thing.weight.value)
+				.forEach(v -> System.out.println("Val " + v));
+		} catch (NullPointerException ex) {
+			ex.printStackTrace();
+		}
+	}
+}
+
+class Thing {
+	Weight weight;
+
+	Thing(int weight) {
+		if (weight % 2 == 0) {
+			this.weight = new Weight(weight);
+		}
+	}
+
+	public Weight getWeight() {
+		return weight;
+	}
+}
+
+class Weight {
+	Integer value;
+
+	Weight(int value) {
+		if (value % 2 == 0) {
+			this.value = value;
+		}
+	}
+
+	public int getValue() {
+		return value;
+	}
+}

java-14/JFREventStreamTest.java

@@ -0,0 +1,79 @@
+import java.time.Duration;
+import java.util.stream.IntStream;
+import java.util.ArrayList;
+
+import jdk.jfr.consumer.RecordingStream;
+
+/***
+ * The profiles configurations is stored in: `$JAVA_HOME/lib/jrf/`
+ */
+public class JFREventStreamTest {
+	public static void main(String[] args) throws InterruptedException {
+		var task = new FibonacciCalculator(Thread.currentThread());
+
+		var thread = new Thread(task, "t-fib");
+		thread.start();
+
+		try (var rs = new RecordingStream()) {
+			rs.enable("jdk.CPULoad").withPeriod(Duration.ofSeconds(1));
+			rs.enable("jdk.GarbageCollection").withPeriod(Duration.ofSeconds(1));
+			rs.enable("jdk.GCHeapSummary").withPeriod(Duration.ofSeconds(1));
+
+			rs.onEvent("jdk.CPULoad", event -> {
+				System.out.printf("\tCPU load: %f%% - %f%%%n",
+					(event.getFloat("jvmUser") * 100),
+					(event.getFloat("machineTotal") * 100)
+				);
+			});
+			rs.onEvent("jdk.GCHeapSummary", event -> {
+				System.out.printf("\tGC - Summary - %s %f MB%n",
+					event.getString("when"),
+					(event.getFloat("heapUsed") / 1_000_000)
+				);
+
+			});
+			rs.onEvent("jdk.GarbageCollection", event -> {
+				System.out.printf("\tGC - Cause %s - Durantion: %.04fms%n", event.getString("cause"), (event.getFloat("duration") / 1_000_000));
+			});
+			rs.startAsync();
+
+			thread.join();
+		}
+
+	}
+}
+
+class FibonacciCalculator implements Runnable {
+	private Thread thread;
+
+	FibonacciCalculator(Thread thread) {
+		this.thread = thread;
+	}
+
+	public void run() {
+		System.out.println("Starting calculation");
+		int number = 40;
+		while (true) {
+			System.out.println("Calculating for " + number);
+			var result = calculate(number);
+			System.out.println("Result for " + number + " is " + result);
+			if (!thread.isAlive()) {
+				System.out.println("Ending calculation");
+				break;
+			}
+
+			number += 5;
+		}
+	}
+
+	/**
+	 * Bad implementation to take much time.
+	 */
+	public long calculate(int n) {
+		if (n <= 1)
+			return 1;
+		var list = new ArrayList<>(n);
+		IntStream.range(0, n).forEach(__ -> list.add(new Object()));
+		return calculate(n - 1) + calculate(n - 2);
+	}
+}

java-14/PackagingTool.java

@@ -0,0 +1,22 @@
+import javax.swing.JOptionPane;
+
+/**
+ * Steps:
+ *
+ * - compile: `javac PackagingTool.java`
+ * - create JAR: `jar -cfe packaging-tool-example.jar PackagingTool PackagingTool.class`
+ * - test JAR: `java -jar packaging-tool-example.jar`
+ * - create the Package: `jpackage --name pack-tool-sample --input . --main-jar packaging-tool-example.jar --main-class PackagingTool`
+ *
+ * Package will generate:
+ * - `dmg` on macOS
+ * - `msi` on Windows
+ * - `app` on Linux
+ */
+public class PackagingTool {
+	public static void main(String[] args) {
+		System.out.println("Main =)");
+		JOptionPane.showMessageDialog(null, "Hello world from self-contained application", null,
+				JOptionPane.INFORMATION_MESSAGE);
+	}
+}

java-14/README.md

@@ -10,10 +10,16 @@ To run each example use: `java --enable-preview --source 14 <FileName.java>`
   * Promotion to standard
 * Text blocks improvements
   * added new flags
-* Patttern  matching for `instanceof`
+* Patttern matching for `instanceof`
   * added as Preview
 * Records
   * added as Preview
+* Helpful NullPointerExpections
+  * flag to enable: `-XX:+ShowCodeDetailsInExceptionMessages`
+* Packaging tool to create self-contained Java applications
+  * bin: `jpackage`
+* JFR Event Stream
+  * [Here](https://github.com/flight-recorder/health-report) is a great example of a tool built
 
 ## JEPs