Demonstrate Optional additions in 9 and 10

Author: Nicolai Parlog

README.md

@@ -116,8 +116,8 @@ Check out the [jpms](http://blog.codefx.org/tag/jpms/) tag on my blog, [this dem
 * ⑪ [I/O](src/main/java/org/codefx/demo/java11/api/io)
 * ⑪ [`Predicate` / `Pattern`](src/main/java/org/codefx/demo/java11/api/predicate)
 * ⑪ [`Collection`](src/main/java/org/codefx/demo/java11/api/collection/ToArray.java)
-* ⑪⑨ `Optional` [in Java 11](src/main/java/org/codefx/demo/java11/api/optional/IsEmpty.java)
-  and [in Java 9](src/main/java/org/codefx/demo/java9/api/optional/Or.java) ([article](http://blog.codefx.org/java/dev/java-9-optional/))
+* ⑪⑩⑨ `Optional` [in Java 11](src/main/java/org/codefx/demo/java11/api/optional/IsEmpty.java), [in Java 10](src/main/java/org/codefx/demo/java10/api/optional/OrElseThrow.java),
+  and [in Java 9](src/main/java/org/codefx/demo/java9/api/optional/Or.java) ([article](http://blog.codefx.org/java/dev/java-9-optional/))^
 * ⑨ [OS processes](src/main/java/org/codefx/demo/java9/api/processes) ([JEP 102](http://openjdk.java.net/jeps/102))
 
 Some of the small changes have their own articles (in which case they are linked), but many don't.

src/main/java/org/codefx/demo/java10/api/optional/OrElseThrow.java

@@ -0,0 +1,23 @@
+package org.codefx.demo.java10.api.optional;
+
+import java.util.Optional;
+import java.util.concurrent.ThreadLocalRandom;
+
+public class OrElseThrow {
+
+	public static void main(String[] args) {
+		Optional<String> randomOptional = createRandomOptional();
+		if (randomOptional.isPresent()) {
+			// `orElseThrow` works exactly like `get`
+			String value = randomOptional.orElseThrow();
+			System.out.println(value);
+		}
+	}
+
+	private static Optional<String> createRandomOptional() {
+		return ThreadLocalRandom.current().nextInt() < 0
+				? Optional.empty()
+				: Optional.of("not empty");
+	}
+
+}

src/main/java/org/codefx/demo/java9/api/optional/Or.java

@@ -16,10 +16,7 @@ public static void main(String[] args) {
 				.forEach(System.out::println);
 	}
 
-	public static Optional load(String id) {
-		// TODO:
-		// chain the `from` methods and return the first non-empty Optional
-		// (if one exists)
+	public static Optional<Customer> load(String id) {
 		return fromMemory(id)
 				.or(() -> fromDisk(id))
 				.or(() -> fromRemote(id));