1 files changed, 125 insertions, 0 deletions
diff --git a/guava/src/com/google/common/collect/SingletonImmutableSet.java b/guava/src/com/google/common/collect/SingletonImmutableSet.java
new file mode 100644
index 0000000..f64aac1
--- /dev/null
+++ b/guava/src/com/google/common/collect/SingletonImmutableSet.java
@@ -0,0 +1,125 @@
+/*
+ * 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 com.google.common.annotations.GwtCompatible;
+import com.google.common.base.Preconditions;
+
+import java.util.Set;
+
+import javax.annotation.Nullable;
+
+/**
+ * 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 public Object[] toArray() {
+    return new Object[] { element };
+  }
+
+  @Override public <T> T[] toArray(T[] array) {
+    if (array.length == 0) {
+      array = ObjectArrays.newArray(array, 1);
+    } else if (array.length > 1) {
+      array[1] = null;
+    }
+    // Writes will produce ArrayStoreException when the toArray() doc requires.
+    Object[] objectArray = array;
+    objectArray[0] = element;
+    return array;
+  }
+
+  @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();
+  }
+}