Update #0 - First Release

sources/main/java/com/google/common/collect/ImmutableEnumSet.java

@@ -0,0 +1,130 @@
+/*
+ * Copyright (C) 2009 The Guava Authors
+ *
+ * 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 com.google.common.collect;
+
+import java.io.Serializable;
+import java.util.Collection;
+import java.util.EnumSet;
+
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * Implementation of {@link ImmutableSet} backed by a non-empty
+ * {@link java.util.EnumSet}.
+ *
+ * @author Jared Levy
+ */
+@GwtCompatible(serializable = true, emulated = true)
+@SuppressWarnings("serial") // we're overriding default serialization
+final class ImmutableEnumSet<E extends Enum<E>> extends ImmutableSet<E> {
+	static <E extends Enum<E>> ImmutableSet<E> asImmutable(EnumSet<E> set) {
+		switch (set.size()) {
+		case 0:
+			return ImmutableSet.of();
+		case 1:
+			return ImmutableSet.of(Iterables.getOnlyElement(set));
+		default:
+			return new ImmutableEnumSet<E>(set);
+		}
+	}
+
+	/*
+	 * Notes on EnumSet and <E extends Enum<E>>:
+	 *
+	 * This class isn't an arbitrary ForwardingImmutableSet because we need to know
+	 * that calling {@code clone()} during deserialization will return an object
+	 * that no one else has a reference to, allowing us to guarantee immutability.
+	 * Hence, we support only {@link EnumSet}.
+	 */
+	private final transient EnumSet<E> delegate;
+
+	private ImmutableEnumSet(EnumSet<E> delegate) {
+		this.delegate = delegate;
+	}
+
+	@Override
+	boolean isPartialView() {
+		return false;
+	}
+
+	@Override
+	public UnmodifiableIterator<E> iterator() {
+		return Iterators.unmodifiableIterator(delegate.iterator());
+	}
+
+	@Override
+	public int size() {
+		return delegate.size();
+	}
+
+	@Override
+	public boolean contains(Object object) {
+		return delegate.contains(object);
+	}
+
+	@Override
+	public boolean containsAll(Collection<?> collection) {
+		return delegate.containsAll(collection);
+	}
+
+	@Override
+	public boolean isEmpty() {
+		return delegate.isEmpty();
+	}
+
+	@Override
+	public boolean equals(Object object) {
+		return object == this || delegate.equals(object);
+	}
+
+	private transient int hashCode;
+
+	@Override
+	public int hashCode() {
+		int result = hashCode;
+		return (result == 0) ? hashCode = delegate.hashCode() : result;
+	}
+
+	@Override
+	public String toString() {
+		return delegate.toString();
+	}
+
+	// All callers of the constructor are restricted to <E extends Enum<E>>.
+	@Override
+	Object writeReplace() {
+		return new EnumSerializedForm<E>(delegate);
+	}
+
+	/*
+	 * This class is used to serialize ImmutableEnumSet instances.
+	 */
+	private static class EnumSerializedForm<E extends Enum<E>> implements Serializable {
+		final EnumSet<E> delegate;
+
+		EnumSerializedForm(EnumSet<E> delegate) {
+			this.delegate = delegate;
+		}
+
+		Object readResolve() {
+			// EJ2 #76: Write readObject() methods defensively.
+			return new ImmutableEnumSet<E>(delegate.clone());
+		}
+
+		private static final long serialVersionUID = 0;
+	}
+}