test2.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;

public class NewBehaviourScript : MonoBehaviour
{
    private static System.Type[] types = {
            typeof(Integer),
            typeof(Long),
            typeof(String)};

    public void test(int ID)
    {
        System.Type type = default;
        if (ID >= 0 && ID < types.length) {
            type = types[ID];
        }

        // do something with type
    }
}