How to use C# string Copy

using System;
using System.Windows.Forms;

namespace WindowsApplication1
{
	public partial class Form1 : Form
	{
		public Form1()
		{
			InitializeComponent();
		}

		private void button1_Click(object sender, EventArgs e)
		{
			string str1 = null;
			string str2 = null;

			str1 = "CSharp Copy() test";
			str2 = string.Copy(str1);

			MessageBox.Show(str2); 
		}
	}
}