You also will have to catch or throw the IOException. See below. Not always the best way, but it will get you a result:
public class details {
public static void main( String[] args) throws IOException {
BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
System.out.println("What is your name?");
String name = in.readLine(); ;
System.out.println("Hello " + name);
}
}