Add CompletableFutureExample and SupplyAsyncExampleOne classes to demonstrate CompletableFuture usage

Author: kumarcodes

src/main/java/com/java8/CompletableFutureExample.java

@@ -0,0 +1,30 @@
+package com.java8;
+
+import java.util.concurrent.CompletableFuture;
+
+/**
+ * Demonstrates simple usages of CompletableFuture: supplyAsync and runAsync.
+ * <p>
+ * supplyAsync: runs a Supplier that produces a result and returns a
+ * CompletableFuture<T>. The example calls join() to wait for the result.
+ * <p>
+ * runAsync: runs a Runnable that does not produce a result and returns a
+ * CompletableFuture<Void>. Because runAsync is non-blocking, the program may
+ * exit before the task completes unless the future is awaited (e.g., join()).
+ */
+public class CompletableFutureExample {
+    public static void main(String[] args) {
+        // supplyAsync(): accepts a Supplier<T> and runs it asynchronously (by default
+        // using the ForkJoinPool.commonPool()). It returns a CompletableFuture<T>
+        // that will complete with the supplier's result. Calling join() blocks the
+        // current thread until the result is available (and will rethrow exceptions).
+        CompletableFuture<String> supplyAsyncFuture = CompletableFuture.supplyAsync(() -> "Hello supplyAsync World!");
+        System.out.println(supplyAsyncFuture.join());
+        // runAsync(): accepts a Runnable and runs it asynchronously, returning a
+        // CompletableFuture<Void>. Because it doesn't produce a value, you must
+        // still wait on the returned future (e.g., join()) if you need to ensure
+        // the task completes before program exit.
+        CompletableFuture<Void> runAsyncFuture = CompletableFuture.runAsync(() -> System.out.println("Hello runAsync World!"));
+        runAsyncFuture.join();
+    }
+}

src/main/java/com/java8/SupplyAsyncExampleOne.java

@@ -0,0 +1,7 @@
+package com.java8;
+
+public class SupplyAsyncExampleOne {
+    public static void main(String[] args) {
+
+    }
+}