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Commons Collections example source code file (NullComparator.java)

This example Commons Collections source code file (NullComparator.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" TM.

Java - Commons Collections tags/keywords

comparator, comparator, io, nullcomparator, nullcomparator, nullpointerexception, nullpointerexception, object, object, serializable, util

The Commons Collections NullComparator.java source code

/*
 *  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.collections.comparators;

import java.io.Serializable;
import java.util.Comparator;

/**
 * A Comparator that will compare nulls to be either lower or higher than
 * other objects.
 *
 * @since Commons Collections 2.0
 * @version $Revision: 647116 $ $Date: 2008-04-11 12:23:08 +0100 (Fri, 11 Apr 2008) $ 
 *
 * @author Michael A. Smith
 */
public class NullComparator implements Comparator, Serializable {

    /** Serialization version. */
    private static final long serialVersionUID = -5820772575483504339L;

    /**
     *  The comparator to use when comparing two non-<code>null objects.
     **/
    private Comparator nonNullComparator;

    /**
     *  Specifies whether a <code>null are compared as higher than
     *  non-<code>null objects.
     **/
    private boolean nullsAreHigh;

    //-----------------------------------------------------------------------
    /**
     *  Construct an instance that sorts <code>null higher than any
     *  non-<code>null object it is compared with. When comparing two
     *  non-<code>null objects, the {@link ComparableComparator} is
     *  used.
     **/
    public NullComparator() {
        this(ComparableComparator.getInstance(), true);
    }

    /**
     *  Construct an instance that sorts <code>null higher than any
     *  non-<code>null object it is compared with.  When comparing two
     *  non-<code>null objects, the specified {@link Comparator} is
     *  used.
     *
     *  @param nonNullComparator the comparator to use when comparing two
     *  non-<code>null objects.  This argument cannot be
     *  <code>null
     *
     *  @exception NullPointerException if <code>nonNullComparator is
     *  <code>null
     **/
    public NullComparator(Comparator nonNullComparator) {
        this(nonNullComparator, true);
    }

    /**
     *  Construct an instance that sorts <code>null higher or lower than
     *  any non-<code>null object it is compared with.  When comparing
     *  two non-<code>null objects, the {@link ComparableComparator} is
     *  used.
     *
     *  @param nullsAreHigh a <code>true value indicates that
     *  <code>null should be compared as higher than a
     *  non-<code>null object.  A false value indicates
     *  that <code>null should be compared as lower than a
     *  non-<code>null object.
     **/
    public NullComparator(boolean nullsAreHigh) {
        this(ComparableComparator.getInstance(), nullsAreHigh);
    }
    
    /**
     *  Construct an instance that sorts <code>null higher or lower than
     *  any non-<code>null object it is compared with.  When comparing
     *  two non-<code>null objects, the specified {@link Comparator} is
     *  used.
     *
     *  @param nonNullComparator the comparator to use when comparing two
     *  non-<code>null objects. This argument cannot be
     *  <code>null
     *
     *  @param nullsAreHigh a <code>true value indicates that
     *  <code>null should be compared as higher than a
     *  non-<code>null object.  A false value indicates
     *  that <code>null should be compared as lower than a
     *  non-<code>null object.
     *
     *  @exception NullPointerException if <code>nonNullComparator is
     *  <code>null
     **/
    public NullComparator(Comparator nonNullComparator, boolean nullsAreHigh) {
        this.nonNullComparator = nonNullComparator;
        this.nullsAreHigh = nullsAreHigh;
        
        if(nonNullComparator == null) {
            throw new NullPointerException("null nonNullComparator");
        }
    }

    //-----------------------------------------------------------------------
    /**
     *  Perform a comparison between two objects.  If both objects are
     *  <code>null, a 0 value is returned.  If one object
     *  is <code>null and the other is not, the result is determined on
     *  whether the Comparator was constructed to have nulls as higher or lower
     *  than other objects.  If neither object is <code>null, an
     *  underlying comparator specified in the constructor (or the default) is
     *  used to compare the non-<code>null objects.
     *
     *  @param o1  the first object to compare
     *  @param o2  the object to compare it to.
     *  @return <code>-1 if o1 is "lower" than (less than,
     *  before, etc.) <code>o2; 1 if o1 is
     *  "higher" than (greater than, after, etc.) <code>o2; or
     *  <code>0 if o1 and o2 are equal.
     **/
    public int compare(Object o1, Object o2) {
        if(o1 == o2) { return 0; }
        if(o1 == null) { return (this.nullsAreHigh ? 1 : -1); }
        if(o2 == null) { return (this.nullsAreHigh ? -1 : 1); }
        return this.nonNullComparator.compare(o1, o2);
    }

    //-----------------------------------------------------------------------
    /**
     *  Implement a hash code for this comparator that is consistent with
     *  {@link #equals(Object)}.
     *
     *  @return a hash code for this comparator.
     **/
    public int hashCode() {
        return (nullsAreHigh ? -1 : 1) * nonNullComparator.hashCode();
    }

    /**
     *  Determines whether the specified object represents a comparator that is
     *  equal to this comparator.
     *
     *  @param obj  the object to compare this comparator with.
     *
     *  @return <code>true if the specified object is a NullComparator
     *  with equivalent <code>null comparison behavior
     *  (i.e. <code>null high or low) and with equivalent underlying
     *  non-<code>null object comparators.
     **/
    public boolean equals(Object obj) {
        if(obj == null) { return false; }
        if(obj == this) { return true; }
        if(!obj.getClass().equals(this.getClass())) { return false; }

        NullComparator other = (NullComparator)obj;
    
        return ((this.nullsAreHigh == other.nullsAreHigh) &&
                (this.nonNullComparator.equals(other.nonNullComparator)));
    }

}

Other Commons Collections examples (source code examples)

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