Update #0 - First Release

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

@@ -0,0 +1,81 @@
+/*
+ * 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 java.util.List;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+
+/** An ordering that compares objects according to a given order. */
+@GwtCompatible(serializable = true)
+final class ExplicitOrdering<T> extends Ordering<T> implements Serializable {
+	final ImmutableMap<T, Integer> rankMap;
+
+	ExplicitOrdering(List<T> valuesInOrder) {
+		this(buildRankMap(valuesInOrder));
+	}
+
+	ExplicitOrdering(ImmutableMap<T, Integer> rankMap) {
+		this.rankMap = rankMap;
+	}
+
+	@Override
+	public int compare(T left, T right) {
+		return rank(left) - rank(right); // safe because both are nonnegative
+	}
+
+	private int rank(T value) {
+		Integer rank = rankMap.get(value);
+		if (rank == null) {
+			throw new IncomparableValueException(value);
+		}
+		return rank;
+	}
+
+	private static <T> ImmutableMap<T, Integer> buildRankMap(List<T> valuesInOrder) {
+		ImmutableMap.Builder<T, Integer> builder = ImmutableMap.builder();
+		int rank = 0;
+		for (T value : valuesInOrder) {
+			builder.put(value, rank++);
+		}
+		return builder.build();
+	}
+
+	@Override
+	public boolean equals(@Nullable Object object) {
+		if (object instanceof ExplicitOrdering) {
+			ExplicitOrdering<?> that = (ExplicitOrdering<?>) object;
+			return this.rankMap.equals(that.rankMap);
+		}
+		return false;
+	}
+
+	@Override
+	public int hashCode() {
+		return rankMap.hashCode();
+	}
+
+	@Override
+	public String toString() {
+		return "Ordering.explicit(" + rankMap.keySet() + ")";
+	}
+
+	private static final long serialVersionUID = 0;
+}