Update #0 - First Release

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

@@ -0,0 +1,253 @@
+/*
+ * Copyright (C) 2009 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.Comparator;
+
+import javax.annotation.Nullable;
+
+import com.google.common.annotations.GwtCompatible;
+import com.google.common.primitives.Booleans;
+import com.google.common.primitives.Ints;
+import com.google.common.primitives.Longs;
+
+/**
+ * A utility for performing a chained comparison statement. For example:
+ * 
+ * <pre>
+ *    {@code
+ *
+ *   public int compareTo(Foo that) {
+ *     return ComparisonChain.start()
+ *         .compare(this.aString, that.aString)
+ *         .compare(this.anInt, that.anInt)
+ *         .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
+ *         .result();
+ *   }}
+ * </pre>
+ *
+ * <p>
+ * The value of this expression will have the same sign as the <i>first
+ * nonzero</i> comparison result in the chain, or will be zero if every
+ * comparison result was zero.
+ *
+ * <p>
+ * Performance note: Even though the {@code ComparisonChain} caller always
+ * invokes its {@code compare} methods unconditionally, the {@code
+ * ComparisonChain} implementation stops calling its inputs'
+ * {@link Comparable#compareTo compareTo} and {@link Comparator#compare compare}
+ * methods as soon as one of them returns a nonzero result. This optimization is
+ * typically important only in the presence of expensive {@code compareTo} and
+ * {@code compare} implementations.
+ *
+ * <p>
+ * See the Guava User Guide article on <a href=
+ * "http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained#compare/compareTo">
+ * {@code ComparisonChain}</a>.
+ *
+ * @author Mark Davis
+ * @author Kevin Bourrillion
+ * @since 2.0
+ */
+@GwtCompatible
+public abstract class ComparisonChain {
+	private ComparisonChain() {
+	}
+
+	/**
+	 * Begins a new chained comparison statement. See example in the class
+	 * documentation.
+	 */
+	public static ComparisonChain start() {
+		return ACTIVE;
+	}
+
+	private static final ComparisonChain ACTIVE = new ComparisonChain() {
+		@SuppressWarnings("unchecked")
+		@Override
+		public ComparisonChain compare(Comparable left, Comparable right) {
+			return classify(left.compareTo(right));
+		}
+
+		@Override
+		public <T> ComparisonChain compare(@Nullable T left, @Nullable T right, Comparator<T> comparator) {
+			return classify(comparator.compare(left, right));
+		}
+
+		@Override
+		public ComparisonChain compare(int left, int right) {
+			return classify(Ints.compare(left, right));
+		}
+
+		@Override
+		public ComparisonChain compare(long left, long right) {
+			return classify(Longs.compare(left, right));
+		}
+
+		@Override
+		public ComparisonChain compare(float left, float right) {
+			return classify(Float.compare(left, right));
+		}
+
+		@Override
+		public ComparisonChain compare(double left, double right) {
+			return classify(Double.compare(left, right));
+		}
+
+		@Override
+		public ComparisonChain compareTrueFirst(boolean left, boolean right) {
+			return classify(Booleans.compare(right, left)); // reversed
+		}
+
+		@Override
+		public ComparisonChain compareFalseFirst(boolean left, boolean right) {
+			return classify(Booleans.compare(left, right));
+		}
+
+		ComparisonChain classify(int result) {
+			return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
+		}
+
+		@Override
+		public int result() {
+			return 0;
+		}
+	};
+
+	private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
+
+	private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
+
+	private static final class InactiveComparisonChain extends ComparisonChain {
+		final int result;
+
+		InactiveComparisonChain(int result) {
+			this.result = result;
+		}
+
+		@Override
+		public ComparisonChain compare(@Nullable Comparable left, @Nullable Comparable right) {
+			return this;
+		}
+
+		@Override
+		public <T> ComparisonChain compare(@Nullable T left, @Nullable T right, @Nullable Comparator<T> comparator) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compare(int left, int right) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compare(long left, long right) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compare(float left, float right) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compare(double left, double right) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compareTrueFirst(boolean left, boolean right) {
+			return this;
+		}
+
+		@Override
+		public ComparisonChain compareFalseFirst(boolean left, boolean right) {
+			return this;
+		}
+
+		@Override
+		public int result() {
+			return result;
+		}
+	}
+
+	/**
+	 * Compares two comparable objects as specified by {@link Comparable#compareTo},
+	 * <i>if</i> the result of this comparison chain has not already been
+	 * determined.
+	 */
+	public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);
+
+	/**
+	 * Compares two objects using a comparator, <i>if</i> the result of this
+	 * comparison chain has not already been determined.
+	 */
+	public abstract <T> ComparisonChain compare(@Nullable T left, @Nullable T right, Comparator<T> comparator);
+
+	/**
+	 * Compares two {@code int} values as specified by {@link Ints#compare},
+	 * <i>if</i> the result of this comparison chain has not already been
+	 * determined.
+	 */
+	public abstract ComparisonChain compare(int left, int right);
+
+	/**
+	 * Compares two {@code long} values as specified by {@link Longs#compare},
+	 * <i>if</i> the result of this comparison chain has not already been
+	 * determined.
+	 */
+	public abstract ComparisonChain compare(long left, long right);
+
+	/**
+	 * Compares two {@code float} values as specified by {@link Float#compare},
+	 * <i>if</i> the result of this comparison chain has not already been
+	 * determined.
+	 */
+	public abstract ComparisonChain compare(float left, float right);
+
+	/**
+	 * Compares two {@code double} values as specified by {@link Double#compare},
+	 * <i>if</i> the result of this comparison chain has not already been
+	 * determined.
+	 */
+	public abstract ComparisonChain compare(double left, double right);
+
+	/**
+	 * Compares two {@code boolean} values, considering {@code true} to be less than
+	 * {@code false}, <i>if</i> the result of this comparison chain has not already
+	 * been determined.
+	 *
+	 * @since 12.0
+	 */
+	public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
+
+	/**
+	 * Compares two {@code boolean} values, considering {@code false} to be less
+	 * than {@code true}, <i>if</i> the result of this comparison chain has not
+	 * already been determined.
+	 *
+	 * @since 12.0 (present as {@code compare} since 2.0)
+	 */
+	public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
+
+	/**
+	 * Ends this comparison chain and returns its result: a value having the same
+	 * sign as the first nonzero comparison result in the chain, or zero if every
+	 * result was zero.
+	 */
+	public abstract int result();
+}