Implement iterator design pattern with corresponding test case (#60)

Author: mperor

DesignPatterns/README.md

@@ -13,6 +13,7 @@ with practical examples and best practices for using design patterns to create r
 - [Command](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/command) 📝
 - [Execute Around Method (EAM)](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/eam) ⭕
 - [Interpreter](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/interpreter) 📰
+- [Iterator](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/iterator) 🔄
 - [Mediator](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/mediator) 🗣️
 - [Memento](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/memento) 💾
 - [Observer](src/main/java/pl/mperor/lab/java/design/pattern/behavioral/observer) 👀

DesignPatterns/src/main/java/pl/mperor/lab/java/design/pattern/behavioral/iterator/Worm.java

@@ -0,0 +1,32 @@
+package pl.mperor.lab.java.design.pattern.behavioral.iterator;
+
+import java.util.Arrays;
+import java.util.Iterator;
+import java.util.List;
+
+class Worm implements Iterable<Worm.Segment> {
+
+    private final List<Segment> segments;
+
+    Worm(WormColor... colors) {
+        this.segments = Arrays.stream(colors).map(Segment::new).toList();
+    }
+
+    @Override
+    public Iterator<Segment> iterator() {
+        return segments.iterator();
+    }
+
+    record Segment(WormColor color) {
+    }
+
+    enum WormColor {
+        BLUE,
+        WHITE,
+        RED,
+        GREEN,
+        PURPLE,
+        GRAY,
+        BLACK
+    }
+}

DesignPatterns/src/test/java/pl/mperor/lab/java/design/pattern/behavioral/iterator/WormSegmentIteratorTest.java

@@ -0,0 +1,58 @@
+package pl.mperor.lab.java.design.pattern.behavioral.iterator;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.EnumMap;
+import java.util.List;
+import java.util.Map;
+import java.util.function.Function;
+import java.util.stream.Collectors;
+
+import static pl.mperor.lab.java.design.pattern.behavioral.iterator.Worm.WormColor;
+
+public class WormSegmentIteratorTest {
+
+    @Test
+    public void testWormHasIterableSegments() {
+        var scientist = new Scientist();
+        var worms = scientist.getWorms();
+        var popularityByWormColor = worms.stream()
+                .map(scientist::findDominantColorOfWorm)
+                .collect(Collectors.groupingBy(Function.identity(), Collectors.counting()));
+
+        var dominantColorInWorms = popularityByWormColor.entrySet().stream()
+                .max(Map.Entry.comparingByValue())
+                .map(Map.Entry::getKey)
+                .orElseThrow();
+
+        Assertions.assertEquals(WormColor.GREEN, dominantColorInWorms);
+    }
+
+    private record Scientist() {
+
+        private List<Worm> getWorms() {
+            return List.of(
+                    new Worm(WormColor.RED, WormColor.RED, WormColor.GREEN, WormColor.GREEN, WormColor.RED, WormColor.GREEN, WormColor.BLACK, WormColor.BLACK, WormColor.GREEN, WormColor.WHITE, WormColor.RED, WormColor.WHITE, WormColor.BLUE, WormColor.WHITE, WormColor.WHITE, WormColor.BLACK, WormColor.RED, WormColor.BLACK, WormColor.GREEN, WormColor.GREEN, WormColor.WHITE, WormColor.GREEN, WormColor.BLACK, WormColor.WHITE),
+                    new Worm(WormColor.GREEN, WormColor.RED, WormColor.GREEN, WormColor.GREEN, WormColor.WHITE, WormColor.BLACK, WormColor.GREEN, WormColor.GREEN, WormColor.BLUE, WormColor.WHITE, WormColor.BLACK, WormColor.WHITE, WormColor.GREEN, WormColor.WHITE, WormColor.GREEN, WormColor.BLUE, WormColor.BLUE, WormColor.RED, WormColor.WHITE, WormColor.BLACK),
+                    new Worm(WormColor.RED, WormColor.BLUE, WormColor.GREEN, WormColor.WHITE, WormColor.GREEN, WormColor.BLUE, WormColor.WHITE, WormColor.BLACK, WormColor.RED, WormColor.WHITE, WormColor.GREEN, WormColor.RED, WormColor.RED, WormColor.BLUE, WormColor.GREEN, WormColor.BLUE),
+                    new Worm(WormColor.GREEN, WormColor.RED, WormColor.GREEN, WormColor.BLACK, WormColor.RED, WormColor.BLACK, WormColor.BLACK, WormColor.GREEN, WormColor.RED, WormColor.WHITE, WormColor.WHITE, WormColor.GREEN, WormColor.BLUE, WormColor.RED, WormColor.RED, WormColor.WHITE, WormColor.GREEN, WormColor.BLUE, WormColor.BLUE),
+                    new Worm(WormColor.BLACK, WormColor.BLACK, WormColor.GREEN, WormColor.BLUE, WormColor.BLUE, WormColor.BLACK, WormColor.GREEN, WormColor.GREEN, WormColor.RED, WormColor.GREEN, WormColor.BLUE, WormColor.BLUE, WormColor.BLUE, WormColor.BLUE, WormColor.RED, WormColor.GREEN, WormColor.BLUE, WormColor.BLUE, WormColor.BLACK, WormColor.WHITE, WormColor.BLUE),
+                    new Worm(WormColor.RED, WormColor.RED, WormColor.GREEN, WormColor.GREEN, WormColor.RED, WormColor.RED, WormColor.RED, WormColor.GREEN, WormColor.BLACK, WormColor.RED, WormColor.WHITE, WormColor.GREEN, WormColor.BLUE, WormColor.GREEN, WormColor.BLUE, WormColor.RED, WormColor.BLACK, WormColor.RED),
+                    new Worm(WormColor.BLACK, WormColor.BLUE, WormColor.BLUE, WormColor.WHITE, WormColor.RED, WormColor.GREEN, WormColor.RED, WormColor.RED, WormColor.WHITE, WormColor.RED, WormColor.BLACK, WormColor.BLACK, WormColor.WHITE, WormColor.BLACK, WormColor.RED, WormColor.BLACK, WormColor.WHITE, WormColor.BLACK, WormColor.GREEN),
+                    new Worm(WormColor.RED, WormColor.BLUE, WormColor.WHITE, WormColor.GREEN, WormColor.RED, WormColor.GREEN, WormColor.GREEN, WormColor.BLACK, WormColor.WHITE, WormColor.BLACK, WormColor.RED, WormColor.BLUE, WormColor.GREEN, WormColor.BLACK, WormColor.GREEN)
+            );
+        }
+
+        private WormColor findDominantColorOfWorm(Worm worm) {
+            Map<WormColor, Integer> popularityByWormColor = new EnumMap<>(WormColor.class);
+            for (Worm.Segment segment : worm) {
+                popularityByWormColor.merge(segment.color(), 1, Integer::sum);
+            }
+            return popularityByWormColor.entrySet().stream()
+                    .max(Map.Entry.comparingByValue())
+                    .map(Map.Entry::getKey)
+                    .orElseThrow();
+        }
+    }
+}