Java tutorial
/* * 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 com.google.common.annotations.GwtCompatible; import com.google.common.primitives.Booleans; import com.google.common.primitives.Ints; import com.google.common.primitives.Longs; import java.util.Comparator; import javax.annotation.CheckReturnValue; import javax.annotation.Nullable; /** * 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><b>Note:</b> {@code ComparisonChain} instances are <b>immutable</b>. For * this utility to work correctly, calls must be chained as illustrated above. * * <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= * "https://github.com/google/guava/wiki/CommonObjectUtilitiesExplained#comparecompareto"> * {@code ComparisonChain}</a>. * * @author Mark Davis * @author Kevin Bourrillion * @since 2.0 */ @CheckReturnValue @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); /** * Discouraged synonym for {@link #compareFalseFirst}. * * @deprecated Use {@link #compareFalseFirst}; or, if the parameters passed * are being either negated or reversed, undo the negation or reversal and * use {@link #compareTrueFirst}. * @since 19.0 */ @Deprecated public final ComparisonChain compare(Boolean left, Boolean right) { return compareFalseFirst(left, 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(); }