Question

When we get an object from Hashtable using key, is the object we get an reference, ie if we change property of the class will it affect the object inside the Hashtable?

Answer 1

That will depend on whether the object is a reference or a value type. Example:

public class Foo
{
    public string Bar { get; set; }
}

public struct Baz
{
    public string Bazinga { get; set; }
}

class Program
{
    static void Main()
    {
        var hashtable1 = new Dictionary<string, Foo>
        {
            { "key1", new Foo { Bar = "old bar" } }
        };
        var hashtable2 = new Dictionary<string, Baz>
        {
            { "key1", new  Baz { Bazinga = "old bazinga" } }
        };

        var foo = hashtable1["key1"];
        foo.Bar = "new bar";
        var bar = hashtable2["key1"];
        bar.Bazinga = "new bazinga";

        Console.WriteLine(hashtable1["key1"].Bar);
        Console.WriteLine(hashtable2["key1"].Bazinga);
    }
}

prints:

new bar
old bazinga