function test2() {
		var t = document.getElementById('test').value;
		var reg =/.txt$/;
		if (reg.test(t)) {
			alert("ok");
		} else {
			alert("not ok");
		}
	}

import java.util.regex.Pattern;

public class TestLastIndexOf {
	public static void main(String[] args) {
		String fileName = "asdf.jpg";
		if (isTxtPrefix(fileName)) {
			System.out.println("yes");
		} else {
			System.out.println("no");
		}
	}

	public static boolean isTxtPrefix(String fileName) {
		if (fileName.lastIndexOf(".", fileName.length()) != -1) {
			String prefix = fileName.substring(fileName.lastIndexOf(".",
					fileName.length()));
			if (prefix.equalsIgnoreCase(".txt")) {
				return true;
			} else {
				return false;
			}
		} else {
			System.out.println("error");
		}
		return false;
	}
}