Update #0 - First Release

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

@@ -0,0 +1,88 @@
+/*
+ * 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.io.Serializable;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+
+/** An ordering that treats {@code null} as less than all other values. */
+@GwtCompatible(serializable = true)
+final class NullsFirstOrdering<T> extends Ordering<T> implements Serializable {
+	final Ordering<? super T> ordering;
+
+	NullsFirstOrdering(Ordering<? super T> ordering) {
+		this.ordering = ordering;
+	}
+
+	@Override
+	public int compare(@Nullable T left, @Nullable T right) {
+		if (left == right) {
+			return 0;
+		}
+		if (left == null) {
+			return RIGHT_IS_GREATER;
+		}
+		if (right == null) {
+			return LEFT_IS_GREATER;
+		}
+		return ordering.compare(left, right);
+	}
+
+	@Override
+	public <S extends T> Ordering<S> reverse() {
+		// ordering.reverse() might be optimized, so let it do its thing
+		return ordering.reverse().nullsLast();
+	}
+
+	@SuppressWarnings("unchecked") // still need the right way to explain this
+	@Override
+	public <S extends T> Ordering<S> nullsFirst() {
+		return (Ordering<S>) this;
+	}
+
+	@Override
+	public <S extends T> Ordering<S> nullsLast() {
+		return ordering.nullsLast();
+	}
+
+	@Override
+	public boolean equals(@Nullable Object object) {
+		if (object == this) {
+			return true;
+		}
+		if (object instanceof NullsFirstOrdering) {
+			NullsFirstOrdering<?> that = (NullsFirstOrdering<?>) object;
+			return this.ordering.equals(that.ordering);
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return ordering.hashCode() ^ 957692532; // meaningless
+	}
+
+	@Override
+	public String toString() {
+		return ordering + ".nullsFirst()";
+	}
+
+	private static final long serialVersionUID = 0;
+}