Source code
package com.google.common.collect;
import com.google.common.annotations.GwtCompatible;
import com.google.common.primitives.Booleans;
import com.google.errorprone.annotations.InlineMe;
import java.util.Comparator;
import org.jspecify.annotations.Nullable;
/**
* A utility for performing a chained comparison statement. <b>Note:</b> Java 8+ users should
* generally prefer the methods in {@link Comparator}; see <a href="#java8">below</a>.
*
* <p>Example usage of {@code ComparisonChain}:
*
* {@snippet :
* 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();
* }
* }
*
* <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>.
*
* <h4 id="java8">Java 8+ equivalents</h4>
*
* If you are using Java version 8 or greater, you should generally use the static methods in {@link
* Comparator} instead of {@code ComparisonChain}. The example above can be implemented like this:
*
* {@snippet :
* import static java.util.Comparator.comparing;
* import static java.util.Comparator.nullsLast;
* import static java.util.Comparator.naturalOrder;
*
* ...
* private static final Comparator<Foo> COMPARATOR =
* comparing((Foo foo) -> foo.aString)
* .thenComparing(foo -> foo.anInt)
* .thenComparing(foo -> foo.anEnum, nullsLast(naturalOrder()));
*
* @Override
* public int compareTo(Foo that) {
* return COMPARATOR.compare(this, that);
* }
* }
*
* <p>With method references it is more succinct: {@code comparing(Foo::aString)} for example.
*
* <p>Using {@link Comparator} avoids certain types of bugs, for example when you meant to write
* {@code .compare(a.foo, b.foo)} but you actually wrote {@code .compare(a.foo, a.foo)} or {@code
* .compare(a.foo, b.bar)}. {@code ComparisonChain} also has a potential performance problem that
* {@code Comparator} doesn't: it evaluates all the parameters of all the {@code .compare} calls,
* even when the result of the comparison is already known from previous {@code .compare} calls.
* That can be expensive.
*
* @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") // unsafe; see discussion on supertype
@Override
public ComparisonChain compare(Comparable<?> left, Comparable<?> right) {
return classify(((Comparable<Object>) left).compareTo(right));
}
@Override
public <T extends @Nullable Object> ComparisonChain compare(
@ParametricNullness T left, @ParametricNullness T right, Comparator<T> comparator) {
return classify(comparator.compare(left, right));
}
@Override
public ComparisonChain compare(int left, int right) {
return classify(Integer.compare(left, right));
}
@Override
public ComparisonChain compare(long left, long right) {
return classify(Long.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(Boolean.compare(right, left)); // reversed
}
@Override
public ComparisonChain compareFalseFirst(boolean left, boolean right) {
return classify(Boolean.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(Comparable<?> left, Comparable<?> right) {
return this;
}
@Override
public <T extends @Nullable Object> ComparisonChain compare(
@ParametricNullness T left, @ParametricNullness T right, 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.
*
* <p>This method is declared to accept any 2 {@code Comparable} objects, even if they are not <a
* href="https://docs.oracle.com/javase/tutorial/collections/interfaces/order.html">mutually
* comparable</a>. If you pass objects that are not mutually comparable, this method may throw an
* exception. (The reason for this decision is lost to time, but the reason <i>might</i> be that
* we wanted to support legacy classes that implement the raw type {@code Comparable} (instead of
* implementing {@code Comparable<Foo>}) without producing warnings. If so, we would prefer today
* to produce warnings in that case, and we may change this method to do so in the future. Support
* for raw {@code Comparable} types in Guava in general is tracked as <a
* href="https://github.com/google/guava/issues/989">#989</a>.)
*
* @throws ClassCastException if the parameters are not mutually comparable
*/
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 extends @Nullable Object> ComparisonChain compare(
@ParametricNullness T left, @ParametricNullness T right, Comparator<T> comparator);
/**
* Compares two {@code int} values as specified by {@link Integer#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 Long#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
*/
@InlineMe(replacement = "this.compareFalseFirst(left, right)")
@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.
*
* <p>Java 8+ users: you can get the equivalent from {@link Booleans#trueFirst()}. For example:
*
* <pre>
* Comparator.comparing(Foo::isBar, {@link Booleans#trueFirst()})
* </pre>
*
* @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.
*
* <p>Java 8+ users: you can get the equivalent from {@link Booleans#falseFirst()}. For example:
*
* <pre>
* Comparator.comparing(Foo::isBar, {@link Booleans#falseFirst()})
* </pre>
*
* @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();
}