Improve code readability and debug visibility in multiple classes

In `UsePerson.java` and `RandomDemo.java`, print statements were added to provide more visibility during debug. In `FlatMapDemo.java`, replaced `size() == 0` with `isEmpty()` for checking empty collections, improving code readability and performance. Added a new generator in `RandomDemo.java`, showing usage of the `DoubleStream` with the `Math::random` method.

src/main/java/RandomDemo.java

@@ -1,13 +1,19 @@
 import java.util.OptionalInt;
 import java.util.Random;
+import java.util.stream.DoubleStream;
 import java.util.stream.IntStream;
 
 public class RandomDemo {
+    @SuppressWarnings("SimplifyStreamApiCallChains")
     public static void main(String[] args) {
+        DoubleStream.generate(Math::random)
+                .limit(10)
+                .forEach(System.out::println);
+
         Random r = new Random();
         int sum = IntStream.generate(() -> r.nextInt(10))
                 .limit(10)
-                .map(n -> {
+                .map(n -> {        // this is the peek method
                     System.out.println("n = " + n);
                     return n;
                 })
@@ -22,6 +28,7 @@ public static void main(String[] args) {
                 .peek(System.out::println)
                 .filter(n -> n > 7)
                 .findFirst();
+        System.out.println(first);
 
     }
 }

src/main/java/lambdas/UsePerson.java

@@ -28,6 +28,7 @@ public static void main(String[] args) {
                 // .map(Person::new) // uses the Person(Person) ctr -> Stream<Person>
                 .collect(Collectors.toList());
         System.out.println(people);
+        System.out.println(people.getClass().getName());
 
         Person[] peopleArray = names.stream()
                 .map(Person::new)

src/main/java/streams/FlatMapDemo.java

@@ -44,7 +44,7 @@ public static void main(String[] args) {
         //      stream() on an empty collection already returns an empty stream
         customers.stream()
                 .flatMap(customer ->
-                        customer.getOrders().size() == 0 ? Stream.empty() :
+                        customer.getOrders().isEmpty() ? Stream.empty() :
                                 customer.getOrders().stream())
                 .forEach(System.out::println);