tupleっぽいものをJavaで実装する

Tuples.java

import java.lang.reflect.Field;
import java.util.Date;

public final class Tuples {

    public static void main(String[] args) {
        Tuple3<Integer, String, Date> tpl = Tuples.get(1, "a", new Date());
        System.out.println(tpl._1);
        System.out.println(tpl);
    }

    public static <T1> Tuple1<T1> get(T1 val1) {
        return new Tuple1<T1>(val1);
    }

    public static <T1, T2> Tuple2<T1, T2> get(T1 val1, T2 val2) {
        return new Tuple2<T1, T2>(val1, val2);
    }

    public static <T1, T2, T3> Tuple3<T1, T2, T3> get(T1 val1, T2 val2, T3 val3) {
        return new Tuple3<T1, T2, T3>(val1, val2, val3);
    }

    private static abstract class AbstractTuple {
        @Override public String toString() {
            StringBuilder sb = new StringBuilder("(");
            try {
                for (Field field : getClass().getDeclaredFields())
                    sb.append(field.get(this).toString()).append(',');
            } catch (Exception ex) {
                // 原則ここには来ない
                throw new RuntimeException(ex);
            }
            sb.setCharAt(sb.length() - 1, ')');
            return sb.toString();
        }
    }

    public static final class Tuple1<T1> extends AbstractTuple {
        public final T1 _1;
        Tuple1(T1 val1) {
            _1 = val1;
        }
    }

    public static final class Tuple2<T1, T2> extends AbstractTuple {
        public final T1 _1;
        public final T2 _2;
        Tuple2(T1 val1, T2 val2) {
            _1 = val1; _2 = val2;
        }
    }

    public static final class Tuple3<T1, T2, T3> extends AbstractTuple {
        public final T1 _1;
        public final T2 _2;
        public final T3 _3;
        Tuple3(T1 val1, T2 val2, T3 val3) {
            _1 = val1; _2 = val2; _3 = val3;
        }
    }

    public static final class Tuple4<T1, T2, T3, T4> extends AbstractTuple {
        public final T1 _1;
        public final T2 _2;
        public final T3 _3;
        public final T4 _4;
        Tuple4(T1 val1, T2 val2, T3 val3, T4 val4) {
            _1 = val1; _2 = val2; _3 = val3; _4 = val4;
        }
    }
}