/*
* Copyright 2003-2004 The Apache Software Foundation
*
* 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 org.apache.commons.collections.comparators;
import java.io.Serializable;
import java.util.Comparator;
/**
* A {@link Comparator} for {@link Boolean} objects that can sort either
* true or false first.
* <p>
* @see #getTrueFirstComparator()
* @see #getFalseFirstComparator()
* @see #getBooleanComparator(boolean)
*
* @since Commons Collections 3.0
* @version $Revision: 155406 $ $Date: 2005-02-26 12:55:26 +0000 (Sat, 26 Feb 2005) $
*
* @author Rodney Waldhoff
*/
public final class BooleanComparator implements Comparator, 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);
/** <code>true</code> iff <code>true</code> values sort before <code>false</code> values. */
private boolean trueFirst = false;
//-----------------------------------------------------------------------
/**
* Returns a BooleanComparator instance that sorts
* <code>true</code> values before <code>false</code> 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.
*
* @return the true first singleton BooleanComparator
*/
public static BooleanComparator getTrueFirstComparator() {
return TRUE_FIRST;
}
/**
* Returns a BooleanComparator instance that sorts
* <code>false</code> values before <code>true</code> 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.
*
* @return the false first singleton BooleanComparator
*/
public static BooleanComparator getFalseFirstComparator() {
return FALSE_FIRST;
}
/**
* Returns a BooleanComparator instance that sorts
* <code><i>trueFirst</i></code> values before
* <code>!<i>trueFirst</i></code> 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.
*
* @param trueFirst when <code>true</code>, sort
* <code>true</code> <code>Boolean</code>s before <code>false</code>
* @return a singleton BooleanComparator instance
*/
public static BooleanComparator getBooleanComparator(boolean trueFirst) {
return trueFirst ? TRUE_FIRST : FALSE_FIRST;
}
//-----------------------------------------------------------------------
/**
* Creates a <code>BooleanComparator</code> that sorts
* <code>false</code> values before <code>true</code> 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</code> that sorts
* <code><i>trueFirst</i></code> values before
* <code>!<i>trueFirst</i></code> values.
* <p>
* Please use the static factories instead whenever possible.
*
* @param trueFirst when <code>true</code>, sort
* <code>true</code> boolean values before <code>false</code>
*/
public BooleanComparator(boolean trueFirst) {
this.trueFirst = trueFirst;
}
//-----------------------------------------------------------------------
/**
* Compares two arbitrary Objects.
* When both arguments are <code>Boolean</code>, this method is equivalent to
* {@link #compare(Boolean,Boolean) compare((Boolean)<i>obj1</i>,(Boolean)<i>obj2</i>)}.
* When either argument is not a <code>Boolean</code>, this methods throws
* a {@link ClassCastException}.
*
* @param obj1 the first object to compare
* @param obj2 the second object to compare
* @return negative if obj1 is less, positive if greater, zero if equal
* @throws ClassCastException when either argument is not <code>Boolean</code>
*/
public int compare(Object obj1, Object obj2) {
return compare((Boolean)obj1, (Boolean)obj2);
}
/**
* Compares two non-<code>null</code> <code>Boolean</code> 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</code>
*/
public int compare(Boolean b1, Boolean b2) {
boolean v1 = b1.booleanValue();
boolean v2 = b2.booleanValue();
return (v1 ^ v2) ? ( (v1 ^ trueFirst) ? 1 : -1 ) : 0;
}
//-----------------------------------------------------------------------
/**
* Implement a hash code for this comparator that is consistent with
* {@link #equals(Object) equals}.
*
* @return a hash code for this comparator.
*/
public int hashCode() {
int hash = "BooleanComparator".hashCode();
return trueFirst ? -1 * hash : hash;
}
/**
* Returns <code>true</code> iff <i>that</i> Object is
* is a {@link Comparator} whose ordering is known to be
* equivalent to mine.
* <p>
* This implementation returns <code>true</code>
* iff <code><i>that</i></code> is a {@link BooleanComparator}
* whose value of {@link #sortsTrueFirst()} is equal to mine.
*
* @param object the object to compare to
* @return true if equal
*/
public boolean equals(Object object) {
return (this == object) ||
((object instanceof BooleanComparator) &&
(this.trueFirst == ((BooleanComparator)object).trueFirst));
}
//-----------------------------------------------------------------------
/**
* Returns <code>true</code> iff
* I sort <code>true</code> values before
* <code>false</code> values. In other words,
* returns <code>true</code> iff
* {@link #compare(Boolean,Boolean) compare(Boolean.FALSE,Boolean.TRUE)}
* returns a positive value.
*
* @return the trueFirst flag
*/
public boolean sortsTrueFirst() {
return trueFirst;
}
}