254 lines
7.2 KiB
Java
254 lines
7.2 KiB
Java
/*
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* Copyright (C) 2009 The Guava Authors
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package com.google.common.collect;
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import java.util.Comparator;
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import javax.annotation.Nullable;
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import com.google.common.annotations.GwtCompatible;
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import com.google.common.primitives.Booleans;
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import com.google.common.primitives.Ints;
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import com.google.common.primitives.Longs;
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/**
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* A utility for performing a chained comparison statement. For example:
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*
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* <pre>
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* {@code
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*
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* public int compareTo(Foo that) {
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* return ComparisonChain.start()
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* .compare(this.aString, that.aString)
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* .compare(this.anInt, that.anInt)
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* .compare(this.anEnum, that.anEnum, Ordering.natural().nullsLast())
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* .result();
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* }}
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* </pre>
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*
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* <p>
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* The value of this expression will have the same sign as the <i>first
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* nonzero</i> comparison result in the chain, or will be zero if every
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* comparison result was zero.
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*
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* <p>
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* Performance note: Even though the {@code ComparisonChain} caller always
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* invokes its {@code compare} methods unconditionally, the {@code
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* ComparisonChain} implementation stops calling its inputs'
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* {@link Comparable#compareTo compareTo} and {@link Comparator#compare compare}
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* methods as soon as one of them returns a nonzero result. This optimization is
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* typically important only in the presence of expensive {@code compareTo} and
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* {@code compare} implementations.
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*
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* <p>
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* See the Guava User Guide article on <a href=
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* "http://code.google.com/p/guava-libraries/wiki/CommonObjectUtilitiesExplained#compare/compareTo">
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* {@code ComparisonChain}</a>.
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*
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* @author Mark Davis
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* @author Kevin Bourrillion
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* @since 2.0
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*/
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@GwtCompatible
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public abstract class ComparisonChain {
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private ComparisonChain() {
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}
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/**
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* Begins a new chained comparison statement. See example in the class
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* documentation.
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*/
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public static ComparisonChain start() {
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return ACTIVE;
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}
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private static final ComparisonChain ACTIVE = new ComparisonChain() {
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@SuppressWarnings("unchecked")
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@Override
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public ComparisonChain compare(Comparable left, Comparable right) {
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return classify(left.compareTo(right));
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}
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@Override
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public <T> ComparisonChain compare(@Nullable T left, @Nullable T right, Comparator<T> comparator) {
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return classify(comparator.compare(left, right));
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}
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@Override
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public ComparisonChain compare(int left, int right) {
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return classify(Ints.compare(left, right));
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}
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@Override
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public ComparisonChain compare(long left, long right) {
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return classify(Longs.compare(left, right));
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}
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@Override
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public ComparisonChain compare(float left, float right) {
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return classify(Float.compare(left, right));
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}
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@Override
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public ComparisonChain compare(double left, double right) {
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return classify(Double.compare(left, right));
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}
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@Override
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public ComparisonChain compareTrueFirst(boolean left, boolean right) {
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return classify(Booleans.compare(right, left)); // reversed
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}
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@Override
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public ComparisonChain compareFalseFirst(boolean left, boolean right) {
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return classify(Booleans.compare(left, right));
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}
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ComparisonChain classify(int result) {
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return (result < 0) ? LESS : (result > 0) ? GREATER : ACTIVE;
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}
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@Override
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public int result() {
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return 0;
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}
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};
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private static final ComparisonChain LESS = new InactiveComparisonChain(-1);
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private static final ComparisonChain GREATER = new InactiveComparisonChain(1);
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private static final class InactiveComparisonChain extends ComparisonChain {
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final int result;
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InactiveComparisonChain(int result) {
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this.result = result;
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}
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@Override
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public ComparisonChain compare(@Nullable Comparable left, @Nullable Comparable right) {
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return this;
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}
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@Override
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public <T> ComparisonChain compare(@Nullable T left, @Nullable T right, @Nullable Comparator<T> comparator) {
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return this;
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}
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@Override
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public ComparisonChain compare(int left, int right) {
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return this;
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}
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@Override
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public ComparisonChain compare(long left, long right) {
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return this;
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}
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@Override
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public ComparisonChain compare(float left, float right) {
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return this;
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}
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@Override
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public ComparisonChain compare(double left, double right) {
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return this;
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}
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@Override
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public ComparisonChain compareTrueFirst(boolean left, boolean right) {
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return this;
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}
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@Override
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public ComparisonChain compareFalseFirst(boolean left, boolean right) {
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return this;
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}
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@Override
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public int result() {
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return result;
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}
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}
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/**
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* Compares two comparable objects as specified by {@link Comparable#compareTo},
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* <i>if</i> the result of this comparison chain has not already been
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* determined.
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*/
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public abstract ComparisonChain compare(Comparable<?> left, Comparable<?> right);
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/**
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* Compares two objects using a comparator, <i>if</i> the result of this
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* comparison chain has not already been determined.
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*/
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public abstract <T> ComparisonChain compare(@Nullable T left, @Nullable T right, Comparator<T> comparator);
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/**
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* Compares two {@code int} values as specified by {@link Ints#compare},
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* <i>if</i> the result of this comparison chain has not already been
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* determined.
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*/
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public abstract ComparisonChain compare(int left, int right);
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/**
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* Compares two {@code long} values as specified by {@link Longs#compare},
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* <i>if</i> the result of this comparison chain has not already been
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* determined.
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*/
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public abstract ComparisonChain compare(long left, long right);
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/**
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* Compares two {@code float} values as specified by {@link Float#compare},
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* <i>if</i> the result of this comparison chain has not already been
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* determined.
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*/
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public abstract ComparisonChain compare(float left, float right);
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/**
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* Compares two {@code double} values as specified by {@link Double#compare},
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* <i>if</i> the result of this comparison chain has not already been
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* determined.
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*/
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public abstract ComparisonChain compare(double left, double right);
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/**
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* Compares two {@code boolean} values, considering {@code true} to be less than
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* {@code false}, <i>if</i> the result of this comparison chain has not already
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* been determined.
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*
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* @since 12.0
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*/
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public abstract ComparisonChain compareTrueFirst(boolean left, boolean right);
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/**
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* Compares two {@code boolean} values, considering {@code false} to be less
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* than {@code true}, <i>if</i> the result of this comparison chain has not
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* already been determined.
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*
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* @since 12.0 (present as {@code compare} since 2.0)
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*/
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public abstract ComparisonChain compareFalseFirst(boolean left, boolean right);
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/**
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* Ends this comparison chain and returns its result: a value having the same
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* sign as the first nonzero comparison result in the chain, or zero if every
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* result was zero.
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*/
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public abstract int result();
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}
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