Inside C#, Second Edition: String Handling and Regular Expressions Part 1

using System;

namespace StringInterning
{
	class StringInterningApp
	{
		public class Thing
		{
			private int i;
			public Thing(int i) { this.i = i; }
		}

		[STAThread]
		static void Main(string[] args)
		{
			Thing t1 = new Thing(123);
			Thing t2 = new Thing(123);
			Console.WriteLine(t1 == t2);	// False

			string a = "Hello";
			string b = "Hello";

			Console.WriteLine(a == b);		// True

			string c = String.Copy(a);
			Console.WriteLine(a == c);		// True
			Console.WriteLine((object)a == (object)c);	// False

			Console.WriteLine((object)a == (object)b);	// True
		}
	}
}