Implementing Factory Pattern With Generics in Java (#12895)

* Implementing the factory pattern with generics.

* Did some modifications. Also added unit test.

* Changed the package name.

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/DateNotifier.java

@@ -0,0 +1,11 @@
+package com.baeldung.factoryGeneric;
+
+import java.util.Date;
+
+public class DateNotifier implements Notifier<Date> {
+
+    @Override
+    public void notify(Date date) {
+        System.out.println("Notifying: " + date);
+    }
+}

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/Main.java

@@ -0,0 +1,14 @@
+package com.baeldung.factoryGeneric;
+
+import java.util.Date;
+
+class Main {
+    public static void main(String[] args) {
+        NotifierFactory factory = new NotifierFactory();
+        Notifier<String> stringNotifier = factory.getNotifier(String.class);
+        Notifier<Date> dateNotifier = factory.getNotifier(Date.class);
+
+        stringNotifier.notify("Hello world!");
+        dateNotifier.notify(new Date());
+    }
+}

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/Notifier.java

@@ -0,0 +1,6 @@
+package com.baeldung.factoryGeneric;
+
+public interface Notifier<T> {
+
+    void notify(T obj);
+}

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/NotifierFactory.java

@@ -0,0 +1,17 @@
+package com.baeldung.factoryGeneric;
+
+import java.util.Date;
+
+public class NotifierFactory {
+
+    public <T> Notifier<T> getNotifier(Class<T> c) {
+        if (c == String.class) {
+            return Record.STRING.make();
+        }
+        if (c == Date.class) {
+            return Record.DATE.make();
+        }
+        return null;
+    }
+
+}

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/Record.java

@@ -0,0 +1,20 @@
+package com.baeldung.factoryGeneric;
+
+import java.util.Date;
+
+public enum Record {
+    STRING {
+        @Override
+        public Notifier<String> make() {
+        	return new StringNotifier();
+        }
+    },
+    DATE {
+        @Override
+        public Notifier<Date> make() {
+            return new DateNotifier();
+        }
+    };
+
+    public abstract <T> Notifier<T> make();
+}

patterns-modules/design-patterns-creational/src/main/java/com/baeldung/factorygeneric/StringNotifier.java

@@ -0,0 +1,9 @@
+package com.baeldung.factoryGeneric;
+
+public class StringNotifier implements Notifier<String> {
+
+    @Override
+    public void notify(String str) {
+        System.out.println("Notifying: " + str);
+    }
+}

patterns-modules/design-patterns-creational/src/test/java/com/baeldung/factorygeneric/FactoryGenericUnitTest.java

@@ -0,0 +1,43 @@
+package com.baeldung.factoryGeneric;
+
+import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.*;
+
+import java.util.Date;
+
+// Unit test for the NotifierFactory class.
+public class FactoryGenericUnitTest {
+    
+    // Checks that when the factory is asked to provide a string notifier, the object is an actual string notifier.
+    @Test
+    public void givenStringNotifier_whenEquals_thenTrue() {
+        NotifierFactory factory = new NotifierFactory();
+        Notifier<String> stringNotifier = factory.getNotifier(String.class);
+
+        assertNotNull(stringNotifier, "The object returned by the factory is null!");
+        assertTrue(stringNotifier instanceof Notifier<?>, "The object returned by the factory is not a notifier!");
+    }
+
+    // Checks that when the factory is asked to provide a date notifier, the object is an actual date notifier.
+    @Test
+    public void givenDateNotifier_whenEquals_thenTrue() {
+        NotifierFactory factory = new NotifierFactory();
+        Notifier<Date> dateNotifier = factory.getNotifier(Date.class);
+
+        assertNotNull(dateNotifier, "The object returned by the factory is null!");
+        assertTrue(dateNotifier instanceof Notifier<?>, "The object returned by the factory is not a notifier!");
+    }
+
+    // Checks that when the factory is asked to provide both a date notifier and a string notifier, the objects returned are different.
+    @Test
+    public void givenDateNotifierAndStringNotifier_whenEquals_thenFalse() {
+        NotifierFactory factory = new NotifierFactory();
+        Notifier<String> stringNotifier = factory.getNotifier(String.class);
+        Notifier<Date> dateNotifier = factory.getNotifier(Date.class);
+        
+        assertNotNull(stringNotifier, "The object returned by the factory is null!");
+        assertNotNull(dateNotifier, "The object returned by the factory is null!");
+        assertNotEquals(stringNotifier, dateNotifier, "The string notifier and date notifier objects returned by the factory are actually the same!");
+    }
+
+}