Example type-safe pattern matching [Java]

Expr.java

package com.mkbernard.functional.examples;

import java.util.List;
import java.util.function.Function;

import com.google.common.collect.ImmutableList;

public abstract class Expr<A> {
    public abstract <T> T match(Function<Value<A>, T> value, Function<Add<A>, T> add);

    public static class Value<A> extends Expr<A> {
        private final A value;

        public Value(A value) {
            this.value = value;
        }

        public static <A> Value<A> of(A v) {
            return new Value<>(v);
        }

        @Override
        public <T> T match(Function<Value<A>, T> value, Function<Add<A>, T> add) {
            return value.apply(this);
        }

        public A getValue() {
            return value;
        }
    }

    public static class Add<A> extends Expr<A> {
        private final Expr<A> a;
        private final Expr<A> b;

        public Add(Expr<A> a, Expr<A> b) {
            this.a = a;
            this.b = b;
        }

        public static <A> Add<A> of(Expr<A> a, Expr<A> b) {
            return new Add<>(a, b);
        }

        @Override
        public <T> T match(Function<Value<A>, T> value, Function<Add<A>, T> add) {
            return add.apply(this);
        }

        public Expr<A> getA() {
            return a;
        }

        public Expr<A> getB() {
            return b;
        }
    }

    public static int eval(Expr<Integer> e) {
        return e.match(
                (value) -> value.getValue(),
                (add) -> eval(add.getA()) + eval(add.getB())
        );
    }

    public static <T> List<T> evalOther(Expr<T> e) {
        return e.match(
                (value) -> ImmutableList.of(value.getValue()),
                (add) -> ImmutableList.<T>builder().addAll(evalOther(add.getA())).addAll(evalOther(add.getB())).build()
        );
    }

    public static void main(String[] args) {
        Expr<Integer> e = Add.of(Value.of(1), Value.of(2));
        System.out.println(eval(e));
        System.out.println(evalOther(e));
    }
}