Add a DiscreteResources sub type representing an empty set
This is for ONOS-4281
Change-Id: Ic4b6e2f00555681bb2af39dc1cf764d325ae8744
(cherry picked from commit abdf2df31ce11ed1fa8ee3ee83c6df41dbb2be4e)
diff --git a/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
new file mode 100644
index 0000000..6699787
--- /dev/null
+++ b/core/store/dist/src/main/java/org/onosproject/store/resource/impl/EmptyDiscreteResources.java
@@ -0,0 +1,69 @@
+/*
+ * Copyright 2016-present Open Networking Laboratory
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.store.resource.impl;
+
+import com.google.common.collect.ImmutableSet;
+import org.onosproject.net.resource.DiscreteResource;
+import org.onosproject.net.resource.DiscreteResourceId;
+
+import java.util.List;
+import java.util.Optional;
+import java.util.Set;
+
+/**
+ * Represents an empty set of discrete resource.
+ */
+final class EmptyDiscreteResources implements DiscreteResources {
+ static final DiscreteResources INSTANCE = new EmptyDiscreteResources();
+
+ // for serializer
+ private EmptyDiscreteResources() {}
+
+ @Override
+ public Optional<DiscreteResource> lookup(DiscreteResourceId id) {
+ return Optional.empty();
+ }
+
+ @Override
+ public DiscreteResources difference(DiscreteResources other) {
+ return this;
+ }
+
+ @Override
+ public boolean isEmpty() {
+ return true;
+ }
+
+ @Override
+ public boolean containsAny(List<DiscreteResource> other) {
+ return false;
+ }
+
+ @Override
+ public DiscreteResources add(DiscreteResources other) {
+ return other;
+ }
+
+ @Override
+ public DiscreteResources remove(List<DiscreteResource> removed) {
+ return this;
+ }
+
+ @Override
+ public Set<DiscreteResource> values() {
+ return ImmutableSet.of();
+ }
+}