SquirrelJME/SquirrelJME

// -*- Mode: Java; indent-tabs-mode: t; tab-width: 4 -*-
// ---------------------------------------------------------------------------
// SquirrelJME
//     Copyright (C) Stephanie Gawroriski <xer@multiphasicapps.net>
// ---------------------------------------------------------------------------
// SquirrelJME is under the Mozilla Public License Version 2.0.
// See license.mkd for licensing and copyright information.
// ---------------------------------------------------------------------------

package cc.squirreljme.runtime.cldc.util;

import java.lang.ref.Reference;
import java.lang.ref.WeakReference;
import java.util.Comparator;

/**
 * This is used to compare two values using their natural comparison.
 *
 * @since 2016/09/06
 */
public final class NaturalComparator<V>
    implements Comparator<V>
{
    /** The single instance. */
    private static Reference<NaturalComparator> _REF;
    
    /**
     * Only one is ever needed.
     *
     * @since 2017/11/30
     */
    private NaturalComparator()
    {
    }
    
    /**
     * {@inheritDoc}
     * @since 2016/09/06
     */
    @Override
    @SuppressWarnings({"unchecked"})
    public int compare(V __a, V __b)
    {
        // Consider two nulls to be equal
        boolean na = (__a == null), nb = (__b == null);
        if (na && nb)
            return 0;
        
        // Nulls before non-null
        else if (na && !nb)
            return -1;
        else if (!na && nb)
            return 1;
        
        // Use standard comparison
        return ((Comparable<V>)__a).compareTo(__b);
    }
    
    /**
     * Returns the natural comparator instance.
     *
     * @param <V> The type of value to compare.
     * @return The instance of the natural comparator.
     * @since 2016/09/06
     */
    @SuppressWarnings({"unchecked", "rawtypes"})
    public static final <V> NaturalComparator<V> instance()
    {
        Reference<NaturalComparator> ref = NaturalComparator._REF;
        NaturalComparator rv;
        
        // Cache?
        if (ref == null || null == (rv = ref.get()))
            NaturalComparator._REF = new WeakReference<>(
                (rv = new NaturalComparator()));
        
        // Return it
        return (NaturalComparator<V>)rv;
    }
}