Enhance sorting and stream operations in tests

Updated `StringExercises` with comprehensive stream operations, including sorting, filtering, and using collectors. Refined `SortingTest` by simplifying the sorting logic and removing the intermediate list collection step.

src/test/java/sorting/SortingTest.java

@@ -5,13 +5,13 @@
 
 import java.util.Comparator;
 import java.util.List;
-import java.util.stream.Collectors;
 
 public class SortingTest {
 
     // "Getter" methods on a record match
     // the property name, as in name(), priority()
-    record Project(String name, int priority) {}
+    record Project(String name, int priority) {
+    }
 
     private List<Project> projects;
 
@@ -31,11 +31,9 @@ void setUp() {
     // sort by priority, then by name
     @Test
     public void sortByPriorityThenName() {
-        List<Project> sorted = projects.stream()
-                .sorted(Comparator.comparingInt(Project::priority)
+        projects.stream()
+                .sorted(Comparator.comparingInt(Project::priority).reversed()
                         .thenComparing(Project::name))
-                .collect(Collectors.toList());
-        System.out.println(sorted);
-        System.out.println(projects);
+                .forEach(System.out::println);
     }
 }

src/test/java/streams/StringExercises.java

@@ -2,10 +2,12 @@
 
 import org.junit.jupiter.api.Test;
 
-import java.util.Arrays;
-import java.util.Comparator;
-import java.util.List;
+import java.util.*;
+import java.util.function.Consumer;
 import java.util.function.Function;
+import java.util.function.Predicate;
+import java.util.logging.Logger;
+import java.util.stream.Collectors;
 
 public class StringExercises {
     private final List<String> strings = Arrays.asList("this", "is", "a",
@@ -25,7 +27,8 @@ public int compare(String s1, String s2) {
     @Test
     public void stringLengthSort_lambda() {
         // Use lambda for the Comparator (reverse sort)
-
+        strings.sort((s1, s2) -> s2.length() - s1.length());
+        System.out.println(strings);
         // Use the "sorted" method on Stream
     }
 
@@ -35,33 +38,93 @@ private int compareStrings(String s1, String s2) {
 
     @Test  // Use a lambda that calls 'compareStrings' directly
     public void stringLengthSort_methodCall() {
-
+        strings.sort((s1, s2) -> compareStrings(s1, s2));
+        System.out.println(strings);
     }
 
     @Test  // Use a method ref to 'compareStrings'
     public void stringLengthSort_methodRef() {
-
+        strings.sort(this::compareStrings);
+        System.out.println(strings);
     }
 
     @Test  // Use Comparator.comparingInt
     public void stringLengthSort_comparingInt() {
-
+        strings.sort(Comparator.comparingInt(String::length)
+                .thenComparing(Comparator.naturalOrder()));
+        System.out.println(strings);
     }
 
     @Test
     public void demoCollectors() {
+        List<String> result = strings.stream()
+                .map(String::toUpperCase)
+                .collect(Collectors.toList());
+        System.out.println(result);
+        System.out.println(result.getClass()
+                .getName());
+
         // Get only strings of even length
         // Add them to a LinkedList
+        LinkedList<String> evenLengths = strings.stream()
+                .filter(s -> s.length() % 2 == 0)
+                //.collect(Collectors.toCollection(() -> new LinkedList<>()));
+                .collect(Collectors.toCollection(LinkedList::new));
+        System.out.println(evenLengths);
+        System.out.println(evenLengths.getClass()
+                .getName());
 
         // Add the strings to a map of string to length
+        Map<String, Integer> map = strings.stream()
+                //.collect(Collectors.toMap(s -> s, s -> s.length())); // two lambda expressions
+                //.collect(Collectors.toMap(s -> s, String::length));  // lambda and method ref
+                .collect(Collectors.toMap(Function.identity(), String::length));
+        System.out.println(map);
 
         // Filter out nulls, then print even-length strings
+        List<String> stringsWithNulls = Arrays.asList("this", null, "is", null, "a", "test", null);
+        List<String> evens = stringsWithNulls.stream()
+                //.filter(s -> s != null && s.length() % 2 == 0) // guard condition in a short-circuiting logical AND
+                //.filter(s -> s != null)
+                .filter(Objects::nonNull)
+                .filter(s -> s.length() % 2 == 0)
+                .collect(Collectors.toList());
+        System.out.println(evens);
+
+        Logger logger = Logger.getLogger(StringExercises.class.getName());
+        Consumer<String> log = logger::info;
+        Consumer<String> print = System.out::println;
 
         // Function composition
-
-        // Combine the two predicates and use the result to print non-null, even-length strings
+        Predicate<String> nonNull = Objects::nonNull;
+        Predicate<String> evenLength = s -> s.length() % 2 == 0;
+        stringsWithNulls.stream()
+                .filter(nonNull.and(evenLength))
+                .forEach(log.andThen(print));
 
         // f: A -> B, g: B -> C, (g.f)(x) = g(f(x)), A -> C
+        strings.stream()
+                .forEach(s -> predicateWithFunctionWithConsumer(
+                        nonNull,
+                        Object::toString,
+                        System.out::println, s));
+    }
+
+    private <T> Predicate<T> combineThree(Predicate<T> predicate1,
+                                          Predicate<T> predicate2,
+                                          Predicate<T> predicate3) {
+        return predicate1.and(predicate2)
+                .and(predicate3);
+    }
+
+    private <T, R> void predicateWithFunctionWithConsumer(Predicate<T> predicate,
+                                                          Function<T, R> function,
+                                                          Consumer<R> consumer,
+                                                          T t) {
+        if (predicate.test(t)) {
+            R r = function.apply(t);
+            consumer.accept(r);
+        }
     }
 
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