task: Add Composite Entity pattern (#1705)

* add composite entity pattern

* add composite entity pattern

* Update ReactorTest.java

* resolve some code quality problems

* modified a lot

* remove some extra codes

* modified README

* removed the author name and adjusted the spacing

Co-authored-by: zwebrain <11811721@mail.sustech.edu.cn>
Co-authored-by: Subhrodip Mohanta <hello@subho.xyz>

composite-entity/src/main/java/com/iluwatar/compositeentity/App.java

@@ -0,0 +1,38 @@
+package com.iluwatar.compositeentity;
+
+import java.util.Arrays;
+import lombok.extern.slf4j.Slf4j;
+
+
+/**
+ * Composite entity is a Java EE Software design pattern and it is used to model, represent, and
+ * manage a set of interrelated persistent objects rather than representing them as individual
+ * fine-grained entity beans, and also a composite entity bean represents a graph of objects.
+ */
+@Slf4j
+public class App {
+
+
+  /**
+   * An instance that a console manages two related objects.
+   */
+  public App(String message, String signal) {
+    var console = new CompositeEntity();
+    console.init();
+    console.setData(message, signal);
+    Arrays.stream(console.getData()).forEach(LOGGER::info);
+    console.setData("Danger", "Red Light");
+    Arrays.stream(console.getData()).forEach(LOGGER::info);
+  }
+
+  /**
+   * Program entry point.
+   *
+   * @param args command line args
+   */
+  public static void main(String[] args) {
+
+    new App("No Danger", "Green Light");
+
+  }
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/CoarseGrainedObject.java

@@ -0,0 +1,23 @@
+package com.iluwatar.compositeentity;
+
+import java.util.Arrays;
+import java.util.stream.IntStream;
+
+/**
+ * A coarse-grained object is an object with its own life cycle manages its own relationships to
+ * other objects. It can be an object contained in the composite entity, or, composite entity itself
+ * can be the coarse-grained object which holds dependent objects.
+ */
+
+public abstract class CoarseGrainedObject<T> {
+
+  DependentObject<T>[] dependentObjects;
+
+  public void setData(T... data) {
+    IntStream.range(0, data.length).forEach(i -> dependentObjects[i].setData(data[i]));
+  }
+
+  public T[] getData() {
+    return (T[]) Arrays.stream(dependentObjects).map(DependentObject::getData).toArray();
+  }
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/CompositeEntity.java

@@ -0,0 +1,23 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * Composite entity is the coarse-grained entity bean which may be the coarse-grained object, or may
+ * contain a reference to the coarse-grained object.
+ */
+
+public class CompositeEntity {
+
+  private final ConsoleCoarseGrainedObject console = new ConsoleCoarseGrainedObject();
+
+  public void setData(String message, String signal) {
+    console.setData(message, signal);
+  }
+
+  public String[] getData() {
+    return console.getData();
+  }
+
+  public void init() {
+    console.init();
+  }
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/ConsoleCoarseGrainedObject.java

@@ -0,0 +1,20 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * A specific CoarseGrainedObject to implement a console.
+ */
+
+public class ConsoleCoarseGrainedObject extends CoarseGrainedObject<String> {
+
+  @Override
+  public String[] getData() {
+    return new String[]{
+        dependentObjects[0].getData(), dependentObjects[1].getData()
+    };
+  }
+
+  public void init() {
+    dependentObjects = new DependentObject[]{
+        new MessageDependentObject(), new SignalDependentObject()};
+  }
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/DependentObject.java

@@ -0,0 +1,20 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * It is an object, which can contain other dependent objects (there may be a tree of objects within
+ * the composite entity), that depends on the coarse-grained object and has its life cycle managed
+ * by the coarse-grained object.
+ */
+
+public abstract class DependentObject<T> {
+
+  T data;
+
+  public void setData(T message) {
+    this.data = message;
+  }
+
+  public T getData() {
+    return data;
+  }
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/MessageDependentObject.java

@@ -0,0 +1,9 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * The first DependentObject to show message.
+ */
+
+public class MessageDependentObject extends DependentObject<String> {
+
+}

composite-entity/src/main/java/com/iluwatar/compositeentity/SignalDependentObject.java

@@ -0,0 +1,9 @@
+package com.iluwatar.compositeentity;
+
+/**
+ * The second DependentObject to show message.
+ */
+
+public class SignalDependentObject extends DependentObject<String> {
+
+}

composite-entity/src/test/java/com/iluwatar/compositeentity/AppTest.java

@@ -0,0 +1,25 @@
+package com.iluwatar.compositeentity;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * com.iluwatar.compositeentity.App running test
+ */
+class AppTest {
+
+  /**
+   * Issue: Add at least one assertion to this test case.
+   * <p>
+   * Solution: Inserted assertion to check whether the execution of the main method in {@link
+   * App#main(String[])} throws an exception.
+   */
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+
+    assertDoesNotThrow(() -> App.main(new String[]{}));
+
+  }
+}

composite-entity/src/test/java/com/iluwatar/compositeentity/PersistenceTest.java

@@ -0,0 +1,32 @@
+package com.iluwatar.compositeentity;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class PersistenceTest {
+
+  final static ConsoleCoarseGrainedObject console = new ConsoleCoarseGrainedObject();
+
+  @Test
+  void dependentObjectChangedForPersistenceTest() {
+    MessageDependentObject dependentObject = new MessageDependentObject();
+    console.init();
+    console.dependentObjects[0] = dependentObject;
+    String message = "Danger";
+    assertNull(console.dependentObjects[0].getData());
+    dependentObject.setData(message);
+    assertEquals(message, console.dependentObjects[0].getData());
+  }
+
+  @Test
+  void coarseGrainedObjectChangedForPersistenceTest() {
+    MessageDependentObject dependentObject = new MessageDependentObject();
+    console.init();
+    console.dependentObjects[0] = dependentObject;
+    String message = "Danger";
+    assertNull(console.dependentObjects[0].getData());
+    console.setData(message);
+    assertEquals(message, dependentObject.getData());
+  }
+}