java pair提高效率

/** A generic class for pairs.
 *
 *  <p><b>This is NOT part of any supported API.
 *  If you write code that depends on this, you do so at your own risk.
 *  This code and its internal interfaces are subject to change or
 *  deletion without notice.</b>
 */
public class Pair<A, B>
{
   
    public final A fst;
   
    public final B snd;
   
    public Pair(A fst, B snd)
    {
        this.fst = fst;
        this.snd = snd;
    }
   
    public String toString()
    {
        return "Pair[" + fst + "," + snd + "]";
    }
   
    private static boolean equals(Object x, Object y)
    {
        return (x == null && y == null) || (x != null && x.equals(y));
    }
   
    public boolean equals(Object other)
    {
        return other instanceof Pair<?, ?> && equals(fst, ((Pair<?, ?>)other).fst)
            && equals(snd, ((Pair<?, ?>)other).snd);
    }
   
    public int hashCode()
    {
        if (fst == null)
            return (snd == null) ? 0 : snd.hashCode() + 1;
        else if (snd == null)
            return fst.hashCode() + 2;
        else
            return fst.hashCode() * 17 + snd.hashCode();
    }
   
    public static <A, B> Pair<A, B> of(A a, B b)
    {
        return new Pair<A, B>(a, b);
    }
}