/*
* 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.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>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();
}