IndexOf Logic in Java

Logic of the following function:

IndexOf(String,Sub String) – Gives the position of the first occurrence of the substring.

Please check and comment.

import java.io.IOException;
import javax.servlet.http.*;

@SuppressWarnings("serial")
public class TestIndexOf extends HttpServlet {
	public void doGet(HttpServletRequest req, HttpServletResponse resp)
			throws IOException {
		resp.setContentType("text/plain");
		resp.getWriter().println("String IndexOf Implementation...");

		resp.getWriter().println("Pos = " + IndexOf("Hello Jeetu", "llo"));

	}

	public int IndexOf(String main, String sub) {

		char[] mainc = main.toCharArray();
		char[] subc = sub.toCharArray();

		for (int i = 0; i < mainc.length; i++) {
			if (mainc[i] == subc[0]) {
				for (int j = 0; j < subc.length; j++) {
					if (mainc[i + j] != subc[j])
						break;
					else if (j == subc.length - 1)
						return i + 1;
				}

			}
		}
		return -1;
	}
}