Update #0 - First Release

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

@@ -0,0 +1,120 @@
+/*
+ * Copyright (C) 2007 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.util.Set;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+import com.google.common.base.Preconditions;
+
+/**
+ * Implementation of {@link ImmutableSet} with exactly one element.
+ *
+ * @author Kevin Bourrillion
+ * @author Nick Kralevich
+ */
+@GwtCompatible(serializable = true, emulated = true)
+@SuppressWarnings("serial") // uses writeReplace(), not default serialization
+final class SingletonImmutableSet<E> extends ImmutableSet<E> {
+
+	final transient E element;
+	// This is transient because it will be recalculated on the first
+	// call to hashCode().
+	//
+	// A race condition is avoided since threads will either see that the value
+	// is zero and recalculate it themselves, or two threads will see it at
+	// the same time, and both recalculate it. If the cachedHashCode is 0,
+	// it will always be recalculated, unfortunately.
+	private transient int cachedHashCode;
+
+	SingletonImmutableSet(E element) {
+		this.element = Preconditions.checkNotNull(element);
+	}
+
+	SingletonImmutableSet(E element, int hashCode) {
+		// Guaranteed to be non-null by the presence of the pre-computed hash code.
+		this.element = element;
+		cachedHashCode = hashCode;
+	}
+
+	@Override
+	public int size() {
+		return 1;
+	}
+
+	@Override
+	public boolean isEmpty() {
+		return false;
+	}
+
+	@Override
+	public boolean contains(Object target) {
+		return element.equals(target);
+	}
+
+	@Override
+	public UnmodifiableIterator<E> iterator() {
+		return Iterators.singletonIterator(element);
+	}
+
+	@Override
+	boolean isPartialView() {
+		return false;
+	}
+
+	@Override
+	int copyIntoArray(Object[] dst, int offset) {
+		dst[offset] = element;
+		return offset + 1;
+	}
+
+	@Override
+	public boolean equals(@Nullable Object object) {
+		if (object == this) {
+			return true;
+		}
+		if (object instanceof Set) {
+			Set<?> that = (Set<?>) object;
+			return that.size() == 1 && element.equals(that.iterator().next());
+		}
+		return false;
+	}
+
+	@Override
+	public final int hashCode() {
+		// Racy single-check.
+		int code = cachedHashCode;
+		if (code == 0) {
+			cachedHashCode = code = element.hashCode();
+		}
+		return code;
+	}
+
+	@Override
+	boolean isHashCodeFast() {
+		return cachedHashCode != 0;
+	}
+
+	@Override
+	public String toString() {
+		String elementToString = element.toString();
+		return new StringBuilder(elementToString.length() + 2).append('[').append(elementToString).append(']')
+				.toString();
+	}
+}