Update #0 - First Release

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

@@ -0,0 +1,101 @@
+/*
+ * Copyright (C) 2008 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 static com.google.common.collect.CollectPreconditions.checkEntryNotNull;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+
+/**
+ * Implementation of {@link ImmutableMap} with exactly one entry.
+ *
+ * @author Jesse Wilson
+ * @author Kevin Bourrillion
+ */
+@GwtCompatible(serializable = true, emulated = true)
+@SuppressWarnings("serial") // uses writeReplace(), not default serialization
+final class SingletonImmutableBiMap<K, V> extends ImmutableBiMap<K, V> {
+
+	final transient K singleKey;
+	final transient V singleValue;
+
+	SingletonImmutableBiMap(K singleKey, V singleValue) {
+		checkEntryNotNull(singleKey, singleValue);
+		this.singleKey = singleKey;
+		this.singleValue = singleValue;
+	}
+
+	private SingletonImmutableBiMap(K singleKey, V singleValue, ImmutableBiMap<V, K> inverse) {
+		this.singleKey = singleKey;
+		this.singleValue = singleValue;
+		this.inverse = inverse;
+	}
+
+	SingletonImmutableBiMap(Entry<? extends K, ? extends V> entry) {
+		this(entry.getKey(), entry.getValue());
+	}
+
+	@Override
+	public V get(@Nullable Object key) {
+		return singleKey.equals(key) ? singleValue : null;
+	}
+
+	@Override
+	public int size() {
+		return 1;
+	}
+
+	@Override
+	public boolean containsKey(@Nullable Object key) {
+		return singleKey.equals(key);
+	}
+
+	@Override
+	public boolean containsValue(@Nullable Object value) {
+		return singleValue.equals(value);
+	}
+
+	@Override
+	boolean isPartialView() {
+		return false;
+	}
+
+	@Override
+	ImmutableSet<Entry<K, V>> createEntrySet() {
+		return ImmutableSet.of(Maps.immutableEntry(singleKey, singleValue));
+	}
+
+	@Override
+	ImmutableSet<K> createKeySet() {
+		return ImmutableSet.of(singleKey);
+	}
+
+	transient ImmutableBiMap<V, K> inverse;
+
+	@Override
+	public ImmutableBiMap<V, K> inverse() {
+		// racy single-check idiom
+		ImmutableBiMap<V, K> result = inverse;
+		if (result == null) {
+			return inverse = new SingletonImmutableBiMap<V, K>(singleValue, singleKey, this);
+		} else {
+			return result;
+		}
+	}
+}