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package org.javimmutable.collections.tree;

import javax.annotation.concurrent.Immutable;
import java.io.Serializable;
import java.util.Comparator;

/**
 * Comparator that uses the associated type's own compareTo() method.
 * Places null values before non-null values in its ordering.
 */
@Immutable
public final class ComparableComparator>
    implements Comparator,
               Serializable
{
    private static final ComparableComparator INSTANCE = new ComparableComparator();
    private static final long serialVersionUID = -121805;

    /**
     * Creates a type appropriate reference to the singleton instance of this class.
     */
    @SuppressWarnings("unchecked")
    public static > ComparableComparator of()
    {
        return INSTANCE;
    }

    @Override
    public int compare(V a,
                       V b)
    {
        if (a == null) {
            return (b == null) ? 0 : -1;
        }
        if (b == null) {
            return 1;
        }
        return a.compareTo(b);
    }

    @Override
    public int hashCode()
    {
        return 3571; // prime number
    }

    @Override
    public boolean equals(Object o)
    {
        return (o == this) || (o.getClass() == this.getClass());
    }

    private Object readResolve()
    {
        return INSTANCE;
    }
}