Issue #1043: Moved EmptyTopicPath from ImmutableTopicPathBuilder …

…to package level. Added a unit test.

Signed-off-by: Juergen Fickel <juergen.fickel@bosch.io>

protocol-adapter/src/main/java/org/eclipse/ditto/protocoladapter/EmptyTopicPath.java

@@ -0,0 +1,131 @@
+/*
+ * Copyright (c) 2021 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.protocoladapter;
+
+import java.util.Optional;
+
+import javax.annotation.Nullable;
+import javax.annotation.concurrent.Immutable;
+
+/**
+ * Implementation of an empty {@link TopicPath}.
+ */
+@Immutable
+final class EmptyTopicPath implements TopicPath {
+
+    private EmptyTopicPath() {
+        super();
+    }
+
+    /**
+     * Returns an instance of {@code EmptyTopicPath}.
+     *
+     * @return the instance.
+     */
+    static EmptyTopicPath getInstance() {
+        return new EmptyTopicPath();
+    }
+
+    /**
+     * @return always {@code null}.
+     */
+    @Override
+    @Nullable
+    public String getNamespace() {
+        return null;
+    }
+
+    /**
+     * @return always {@code null}.
+     */
+    @Override
+    @Nullable
+    public String getEntityName() {
+        return null;
+    }
+
+    /**
+     * @return always {@code null}.
+     */
+    @Override
+    @Nullable
+    public Group getGroup() {
+        return null;
+    }
+
+    /**
+     * @return always {@code null}.
+     */
+    @Override
+    @Nullable
+    public Criterion getCriterion() {
+        return null;
+    }
+
+    /**
+     * @return always {@code null}.
+     */
+    @Override
+    @Nullable
+    public Channel getChannel() {
+        return null;
+    }
+
+    /**
+     * @return always an empty Optional.
+     */
+    @Override
+    public Optional<Action> getAction() {
+        return Optional.empty();
+    }
+
+    /**
+     * @return always an empty Optional.
+     */
+    @Override
+    public Optional<SearchAction> getSearchAction() {
+        return Optional.empty();
+    }
+
+    /**
+     * @return always an empty Optional.
+     */
+    @Override
+    public Optional<String> getSubject() {
+        return Optional.empty();
+    }
+
+    /**
+     * @return always an empty String.
+     */
+    @Override
+    public String getPath() {
+        return "";
+    }
+
+    @Override
+    public boolean equals(@Nullable final Object o) {
+        return this == o || !(o == null || getClass() != o.getClass());
+    }
+
+    @Override
+    public int hashCode() {
+        return EmptyTopicPath.class.hashCode();
+    }
+
+    @Override
+    public String toString() {
+        return getClass().getSimpleName() + "[]";
+    }
+
+}

protocol-adapter/src/main/java/org/eclipse/ditto/protocoladapter/ImmutableTopicPathBuilder.java

@@ -15,8 +15,6 @@
 import static java.util.Objects.requireNonNull;
 import static org.eclipse.ditto.model.base.common.ConditionChecker.checkNotNull;
 
-import java.util.Optional;
-
 import javax.annotation.concurrent.NotThreadSafe;
 
 import org.eclipse.ditto.model.base.entity.id.NamespacedEntityId;
@@ -45,15 +43,6 @@ private ImmutableTopicPathBuilder(final String namespace, final String name) {
         this.name = name;
     }
 
-    /**
-     * Returns an empty {@code TopicPath}.
-     *
-     * @return the topic path.
-     */
-    public static TopicPath empty() {
-        return EmptyTopicPath.newInstance();
-    }
-
     /**
      * Returns a new TopicPathBuilder for the specified {@code entityId}. The {@code namespace} and {@code id} part of
      * the {@code TopicPath} will pe parsed from the {@code entityId} and set in the builder.
@@ -294,73 +283,4 @@ public TopicPath build() {
         }
     }
 
-    /**
-     * Implementation of {@link TopicPath} with an empty path.
-     */
-    private static class EmptyTopicPath implements TopicPath {
-
-        private EmptyTopicPath() {
-            // no-op
-        }
-
-        static EmptyTopicPath newInstance() {
-            return new EmptyTopicPath();
-        }
-
-        @Override
-        public String getNamespace() {
-            return null;
-        }
-
-        @Override
-        public String getEntityName() {
-            return null;
-        }
-
-        @Override
-        public Group getGroup() {
-            return null;
-        }
-
-        @Override
-        public Criterion getCriterion() {
-            return null;
-        }
-
-        @Override
-        public Channel getChannel() {
-            return null;
-        }
-
-        @Override
-        public Optional<Action> getAction() {
-            return Optional.empty();
-        }
-
-        @Override
-        public Optional<SearchAction> getSearchAction() {
-            return Optional.empty();
-        }
-
-        @Override
-        public Optional<String> getSubject() {
-            return Optional.empty();
-        }
-
-        @Override
-        public String getPath() {
-            return "";
-        }
-
-        @Override
-        public boolean equals(final Object o) {
-            return this == o || !(o == null || getClass() != o.getClass());
-        }
-
-        @Override
-        public int hashCode() {
-            return super.hashCode();
-        }
-    }
-
 }

protocol-adapter/src/main/java/org/eclipse/ditto/protocoladapter/ProtocolFactory.java

@@ -85,7 +85,7 @@ public static Adaptable setExtra(final Adaptable existingAdaptable, final JsonOb
      * @return the topic path.
      */
     public static TopicPath emptyTopicPath() {
-        return ImmutableTopicPathBuilder.empty();
+        return EmptyTopicPath.getInstance();
     }
 
     /**

protocol-adapter/src/test/java/org/eclipse/ditto/protocoladapter/EmptyTopicPathTest.java

@@ -0,0 +1,98 @@
+/*
+ * Copyright (c) 2021 Contributors to the Eclipse Foundation
+ *
+ * See the NOTICE file(s) distributed with this work for additional
+ * information regarding copyright ownership.
+ *
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-2.0
+ *
+ * SPDX-License-Identifier: EPL-2.0
+ */
+package org.eclipse.ditto.protocoladapter;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.mutabilitydetector.unittesting.MutabilityAssert.assertInstancesOf;
+import static org.mutabilitydetector.unittesting.MutabilityMatchers.areImmutable;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import nl.jqno.equalsverifier.EqualsVerifier;
+
+/**
+ * Unit test for {@link EmptyTopicPathTest}.
+ */
+public final class EmptyTopicPathTest {
+
+    private EmptyTopicPath underTest;
+
+    @Before
+    public void setUp() {
+        underTest = EmptyTopicPath.getInstance();
+    }
+
+    @Test
+    public void assertImmutability() {
+        assertInstancesOf(EmptyTopicPath.class, areImmutable());
+    }
+
+    @Test
+    public void testHashCodeAndEquals() {
+        EqualsVerifier.forClass(EmptyTopicPath.class)
+                .usingGetClass()
+                .verify();
+    }
+
+    @Test
+    public void getInstanceReturnsNotNull() {
+        assertThat(EmptyTopicPath.getInstance()).isNotNull();
+    }
+
+    @Test
+    public void getNamespaceReturnsNull() {
+        assertThat(underTest.getNamespace()).isNull();
+    }
+
+    @Test
+    public void getEntityNameReturnsNull() {
+        assertThat(underTest.getEntityName()).isNull();
+    }
+
+    @Test
+    public void getGroupReturnsNull() {
+        assertThat(underTest.getGroup()).isNull();
+    }
+
+    @Test
+    public void getCriterionReturnsNull() {
+        assertThat(underTest.getCriterion()).isNull();
+    }
+
+    @Test
+    public void getChannelReturnsNull() {
+        assertThat(underTest.getChannel()).isNull();
+    }
+
+    @Test
+    public void getActionReturnsEmptyOptional() {
+        assertThat(underTest.getAction()).isEmpty();
+    }
+
+    @Test
+    public void getSearchActionReturnsEmptyOptional() {
+        assertThat(underTest.getSearchAction()).isEmpty();
+    }
+
+    @Test
+    public void getSubjectReturnsEmptyOptional() {
+        assertThat(underTest.getSubject()).isEmpty();
+    }
+
+    @Test
+    public void getPathReturnsEmptyString() {
+        assertThat(underTest.getPath()).isEmpty();
+    }
+
+}