Refactor LazyStreams class and update SummarizingDemo

Removed unused logger from LazyStreams class and rearranged order of stream operations for better readability. Modified behavior for handling empty streams in FlatMapDemo. Added functionality to generate a list of random doubles in SummarizingDemo. Also, made miscellaneous changes to improve code readability and maintainability.

src/main/java/SummarizingDemo.java

@@ -1,8 +1,16 @@
 import java.util.DoubleSummaryStatistics;
+import java.util.List;
 import java.util.stream.DoubleStream;
 
 public class SummarizingDemo {
     public static void main(String[] args) {
+        List<Double> collect = DoubleStream.generate(Math::random)
+                .limit(10)
+                .boxed()
+                .toList();
+        System.out.println(collect);
+
+
         DoubleSummaryStatistics stats = DoubleStream.generate(Math::random)
                 .limit(1_000_000)
                 .summaryStatistics();

src/main/java/lambdas/UsePerson.java

@@ -7,6 +7,7 @@
 import java.util.stream.Collectors;
 
 public class UsePerson {
+    @SuppressWarnings("Convert2MethodRef")
     public static void main(String[] args) {
         List<String> names = Arrays.asList("John", "Paul", "George", "Ringo");
 
@@ -26,8 +27,7 @@ public static void main(String[] args) {
         people = names.stream()
                 .map(Person::new) // uses the Person(String) ctr
                 .peek(person -> System.out.println(person + " processed by " +
-                                                   Thread.currentThread()
-                                                           .getName()))
+                                                   Thread.currentThread().getName()))
                 // .map(Person::new) // uses the Person(Person) ctr
                 .collect(Collectors.toList());
         System.out.println(people);

src/main/java/lazy/LazyStreams.java

@@ -1,11 +1,8 @@
 package lazy;
 
-import java.util.logging.Logger;
 import java.util.stream.IntStream;
 
 public class LazyStreams {
-    private static final Logger logger = Logger.getLogger(LazyStreams.class.getName());
-
     public static int multByTwo(int n) {
         System.out.printf("Inside multByTwo with arg %d on thread %s%n",
                 n, Thread.currentThread().getName());
@@ -23,16 +20,16 @@ public static void main(String[] args) {
         int firstEvenDoubleDivBy3 = IntStream.rangeClosed(100, 200)
                 .map(n -> n * 2)
                 .filter(n -> n % 3 == 0)
-                .findFirst().orElse(0);
+                .findFirst().orElseThrow();
         System.out.println(firstEvenDoubleDivBy3);
 
 
         // Demonstrate laziness using print statements
         firstEvenDoubleDivBy3 = IntStream.rangeClosed(100, 2_000_000)
                 // .parallel()
-                .filter(LazyStreams::modByThree)
                 .map(LazyStreams::multByTwo)
-                .findFirst().orElse(0);
+                .filter(LazyStreams::modByThree)
+                .findAny().orElse(0);
         System.out.printf("First even divisible by 3 is %d%n", firstEvenDoubleDivBy3);
     }
 }

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);