BooleanComparator.java
- /*
- * Licensed to the Apache Software Foundation (ASF) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * The ASF licenses this file to You 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 org.apache.commons.collections4.comparators;
- import java.io.Serializable;
- import java.util.Comparator;
- /**
- * A {@link Comparator} for {@link Boolean} objects that can sort either
- * true or false first.
- *
- * @see #getTrueFirstComparator()
- * @see #getFalseFirstComparator()
- * @see #booleanComparator(boolean)
- * @since 3.0
- */
- public final class BooleanComparator implements Comparator<Boolean>, Serializable {
- /** Serialization version. */
- private static final long serialVersionUID = 1830042991606340609L;
- /** Constant "true first" reference. */
- private static final BooleanComparator TRUE_FIRST = new BooleanComparator(true);
- /** Constant "false first" reference. */
- private static final BooleanComparator FALSE_FIRST = new BooleanComparator(false);
- /**
- * Returns a BooleanComparator instance that sorts
- * {@code <em>trueFirst</em>} values before
- * {@code !<em>trueFirst</em>} values.
- * <p>
- * Clients are encouraged to use the value returned from
- * this method instead of constructing a new instance
- * to reduce allocation and garbage collection overhead when
- * multiple BooleanComparators may be used in the same
- * virtual machine.
- * </p>
- *
- * @param trueFirst when {@code true}, sort
- * {@code true} {@code Boolean}s before {@code false}
- * @return a singleton BooleanComparator instance
- * @since 4.0
- */
- public static BooleanComparator booleanComparator(final boolean trueFirst) {
- return trueFirst ? TRUE_FIRST : FALSE_FIRST;
- }
- /**
- * Gets a BooleanComparator instance that sorts
- * {@code false} values before {@code true} values.
- * <p>
- * Clients are encouraged to use the value returned from
- * this method instead of constructing a new instance
- * to reduce allocation and garbage collection overhead when
- * multiple BooleanComparators may be used in the same
- * virtual machine.
- * </p>
- *
- * @return the false first singleton BooleanComparator
- */
- public static BooleanComparator getFalseFirstComparator() {
- return FALSE_FIRST;
- }
- /**
- * Gets a BooleanComparator instance that sorts
- * {@code true} values before {@code false} values.
- * <p>
- * Clients are encouraged to use the value returned from
- * this method instead of constructing a new instance
- * to reduce allocation and garbage collection overhead when
- * multiple BooleanComparators may be used in the same
- * virtual machine.
- * </p>
- *
- * @return the true first singleton BooleanComparator
- */
- public static BooleanComparator getTrueFirstComparator() {
- return TRUE_FIRST;
- }
- /** {@code true} iff {@code true} values sort before {@code false} values. */
- private final boolean trueFirst;
- /**
- * Creates a {@code BooleanComparator} that sorts
- * {@code false} values before {@code true} values.
- * <p>
- * Equivalent to {@link #BooleanComparator(boolean) BooleanComparator(false)}.
- * <p>
- * Please use the static factory instead whenever possible.
- */
- public BooleanComparator() {
- this(false);
- }
- /**
- * Creates a {@code BooleanComparator} that sorts
- * {@code <em>trueFirst</em>} values before
- * {@code !<em>trueFirst</em>} values.
- * <p>
- * Please use the static factories instead whenever possible.
- *
- * @param trueFirst when {@code true}, sort
- * {@code true} boolean values before {@code false}
- */
- public BooleanComparator(final boolean trueFirst) {
- this.trueFirst = trueFirst;
- }
- /**
- * Compares two non-{@code null} {@code Boolean} objects
- * according to the value of {@link #sortsTrueFirst()}.
- *
- * @param b1 the first boolean to compare
- * @param b2 the second boolean to compare
- * @return negative if obj1 is less, positive if greater, zero if equal
- * @throws NullPointerException when either argument {@code null}
- */
- @Override
- public int compare(final Boolean b1, final Boolean b2) {
- final boolean v1 = b1.booleanValue();
- final boolean v2 = b2.booleanValue();
- return v1 ^ v2 ? v1 ^ trueFirst ? 1 : -1 : 0;
- }
- /**
- * Returns {@code true} iff <em>that</em> Object is
- * a {@link Comparator} whose ordering is known to be
- * equivalent to mine.
- * <p>
- * This implementation returns {@code true}
- * iff {@code <em>that</em>} is a {@link BooleanComparator}
- * whose value of {@link #sortsTrueFirst()} is equal to mine.
- *
- * @param object the object to compare to
- * @return true if equal
- */
- @Override
- public boolean equals(final Object object) {
- return this == object ||
- object instanceof BooleanComparator &&
- trueFirst == ((BooleanComparator) object).trueFirst;
- }
- /**
- * Implement a hash code for this comparator that is consistent with
- * {@link #equals(Object) equals}.
- *
- * @return a hash code for this comparator.
- */
- @Override
- public int hashCode() {
- final int hash = "BooleanComparator".hashCode();
- return trueFirst ? -1 * hash : hash;
- }
- /**
- * Returns {@code true} iff
- * I sort {@code true} values before
- * {@code false} values. In other words,
- * returns {@code true} iff
- * {@link #compare(Boolean,Boolean) compare(Boolean.FALSE,Boolean.TRUE)}
- * returns a positive value.
- *
- * @return the trueFirst flag
- */
- public boolean sortsTrueFirst() {
- return trueFirst;
- }
- }